a pitch for thread grinding | cutting tool engineering

a pitch for thread grinding | cutting tool engineering

It may not be a new twist, but thread grinding is still one of the most accurate ways to produce internal and external threads. While single- and multiple-point turning tools, taps and dies, milling cutters, whirling rings and thread rollers have their advantages, thread grinding remains a solid choice for tight-tolerance parts.

Thread accuracy is a sum of many elements, including pitch, helical path, helix angle and major, minor and pitch diameters. A threads lead, or the distance the helix advances in one full turn of the screw, is the most critical dimension in most cases.

This short video provides some insight into the benefits and time savings afforded by a universal grinding machine. It is presented as supplemental information to Cutting Tool Engineering's December 2011 cover story, "A Pitch for Thread Grinding."Video courtesy of United Grinding.

Regarding lead tolerances achieved by different threadmaking methods, Hans Ueltschi, vice president for the cylindrical division of United Grinding Technologies Inc., Miamisburg, Ohio, said, In thread grinding, we typically talk about tolerances in the lower tenths and millionths, whereas turning thread tolerances are more in the upper tenths and thousandths. Grinding machines are typically able to achieve tolerances of about 0.0002 " or tighter.

Consistency is another advantage of thread grinding. You can dress the grinding wheel extremely precisely, and, once you have that form in the wheel, the wheel generally doesnt wear as rapidly as does a single-point tool, Ueltschi said.

Thread grinding can also enhance production flexibility. In a job shop environment, a wheel can be redressed quickly to produce a different thread, while other methods may require different cutting tools.

Jim Vosmik, president of Drake Manufacturing Services Co. Inc., Warren, Ohio, cited production of positioning worms for automotive electronic power steering systems as a typical thread grinding application. A low-quality, threaded worm can produce unwanted noise in the passenger compartment. Key considerations are surface finish, waviness and accuracy of the thread leadnot in overall length, but in each revolution, he said.

Inaccuracyknown as drunkenness or wobbleproduces variations in torque, and the feel of the steering will change. For automotive steering components, customers are looking for a surface finish finer than 0.2m Ra, form compliance on the thread track around 5m and lead variation in one revolution below 3m, Vosmik said. These tolerances are more typical of the highest-quality positioning ballscrews and indexing worms.

Machines engineered to grind threads can be grouped into two broad categories: universal cylindrical grinders with thread grinding capability and dedicated thread grinders. The machine styles differ in the way they apply the wheel, how the wheel interacts with the part and the number of setups required to produce a part.

In a universal grinding machine fitted for thread grinding, the grinding wheel typically is not tilted to produce the threads helix angle. We call it axis parallel thread grinding, Ueltschi said. The wheel spindle axis is parallel to the workpiece axis. The thread form dressing is adjusted to compensate for not tilting the wheel; we actually dress it wrong so it comes out right. If we dressed the wheel with the normal thread form and then cut the thread with the wheel parallel, the thread would have an error. The machines grinding software controls dressing.

There are, however, limits to the helix angles that can be produced via axis parallel thread grinding. For ODs, the limit is generally 6, according to Ueltschi. Grinding ID threads on a universal machine is further limited because fitting the grinding wheel and quill into the ID bore creates additional issues. Therefore, on ID threads you would have to go to a tilting A-axis arbor more quickly than you would on the OD side, Ueltschi said, noting that the limit is about 3 before having to go to a tilting wheel arbor.

United Grindings Studer Thread software calculates potential error and compensates in the dressing subroutine. After a user enters thread specifications into the menu-driven software, the program determines whether or not the thread can be produced on the machine, what compensation is required and dressing and cycle times. A variety of grinding cycles enable a thread to be cut in different ways, depending on the type and geometry of thread, including plunging the thread or chasing it with single- or multiple-rib wheels.

Universal cylindrical machines for thread grinding typically feature turret heads with multiple OD and ID wheels. According to Ueltschi, the main advantage of using a universal machine is its ability to produce an entire part in one setup. For example, we take a gear shaft for a helicopter gearbox, grind the journals and faces and IDs, index the turret to another wheel and grind a precise thread. The old method would have involved putting the part through one or several OD grinders, followed by a thread grinder.

In thread grinding, there is a lot more involved than in turning, but, in the end, if everything is done right, you definitely get a better product, Ueltschi continued. However, grindingwith longer cycle timesmay be a more expensive process. So if you can get away with turning the thread, that is the way to go.

Complete Grinding Solutions, Springboro, Ohio, employs universal cylindrical grinding machines for many conventional applications as well as niche jobs, such as grinding Formula 1 steering racks and camshafts for NASCAR teams. Beat Maurer, CGS co-founder, said about 10 percent of the companys work involves thread grinding.

In addition to part accuracy, thread grinding provides the fine surface finishes required for critical-application parts. Single-point inserts and milling cutters produce larger chips than grinding wheels and the cutting process may induce stress into a part. As a result, Maurer said, For parts such as aircraft pistons, we use low-stress thread grinding to avoid generating heat in the part.

While hard turning may be a threadmaking alternative for less-than-premium-quality parts, tool costs can favor grinding. A wheel is very cheap compared to changing inserts every 3 hours, Maurer said. He added that grinding can also be effective when interrupted threading, where gaps in the toolpath could break an insert.

CGSs performs most of its thread grinding on a Studer S40 universal. Many times, Maurer said, when we do thread grinding it is a combination of complete machining, meaning we do all the part features and then grind a thread as well. He acknowledged that a universal machine sometimes is limited in the helix angles it can produce. You have to design the process and optimize it.

Dedicated thread grinding machines have enabled Mechanitron Corp., Roselle, N.J., to serve a customer base that has continually changed over 5 decades. The shop has moved from threading cores for the plastic molding industry, to grinding components for defense and aerospace manufacturers, to producing actuator screws for medical diagnostic equipment. The shop uses venerable non-CNC J&L thread grinding machines which, according to Dave Newman, president of Mechanitron, can hold lead tolerances within 0.0001 " while handling parts from 0.040 " to 12 " in diameter and 2 " to 105 " long. Tilting wheel arbors permit grinding helix angles up to 31.

Changing the lead of a thread on the J&L thread grinders involves changing the gears that control the lead. Switching gears is routine, said longtime Mechanitron grinder Louis Sayte, and occurs several times daily. The pitch will be whatever gear I put in, he said.

Some customers have unusual requests. People come in with a very strange lead, and then I have to calculate that lead for the gears we have, Sayte said. That is the reason people come to usto give them these oddball leads and still hold them within 0.0001 ".

Sayte pointed out that the J&L thread grinding machines run automatically using electromechanical switches and cams. Wheel speed, work speed and lead are independent of each other. The machines can be set up to perform a fast return between grinding passes or to cut on the forward and return passes. Dressing, also set independently, can be performed on the return pass, after every pass or after a specified number of passes. The machines compensate mechanically for material removed in each dressing pass.

The J&L machines can cut fractional threads, decimal pitches, anything you want, Sayte said. That capability is useful for mold and die jobs. A finished molded part may have a standard-size thread, but the molds thread form dimensions must be adjusted to compensate for shrinkage that occurs during molding. The customer specifies the shrinkage and we give them a longer or shorter lead to compensate, Sayte said. The plastic shrinks, but they still want the proper pitch when the part cools off.

According to Drakes Vosmik, some dedicated CNC thread grinders are riding a wave of high-tech demand. The companys GS:TEM -Mini thread grinders for production-level thread grinding of parts from 0.5mm to 10mm in diameter and up to 100mm long are flying out the door, he said. Most of the machines are going to Asia for making miniature electronic devices.

Vosmik explained that those electronic products typically are held together with fasteners 3mm in diameter and smaller, and manufacturers dont want chips when threading holes for the fasteners. So they are using forming taps, which are essentially rotary progressive dies. Drake machines are used to grind the threads in the taps.

In a forming tap, the thread starts at the minor diameter with no height and grows within a few revolutions to reach the full major diameter, displacing the metal instead of cutting it. Like a fluted tap, the forming tap features a relief that facilitates the cutting action, but, unlike a fluted tool, the relief of a form tap is continuously contoured. It looks like a screw, with no flutes, Vosmik said, but the thread is not the same diameter all the way around.

Drake software engineers Stig Mowatt-Larssen and Mike Hughes wrote the software code that enables the tiny, complex forming taps to be ground accurately. The real value in the machine is our software and process development, Vosmik said.

The forming taps are as small as M0.51.25 (metric tap 0.5mm nominal OD 0.125mm pitch and lead. In inches, 0.020200 or 200 tpi). Vosmik said advances in grinding wheel technology are key to production of the taps (see sidebar on page 32).

The wheels are driving us, he said. The wheel manufacturers are pushing ahead and advancing the capabilities of the thread grinding machines. We are going to see lots of new order-of-magnitude breakthroughs in cycle times and quality.

Vosmik said the unanticipated demand for specialized thread grinding machines demonstrates that manufacturers must be open to nontraditional opportunities. The Mini machine concept began as a retrofit of another machine for a Drake customer and was later developed into a new machine. We kind of married this need for smaller tools with features such as linear motors that permit relieving a cutting edgereversing X-axis motionvery quickly, Vosmik said.CTE

This traverse disc from Saint-Gobain with a 0.002 " corner radius dresses aluminum-oxide grinding wheels employed to grind microthreads on HSS taps.Images above and below courtesy of Saint-Gobain Abrasives.

Mike Hitchiner, OEM technology manager for grinding wheel supplier Saint-Gobain Abrasives, Worcester, Mass., noted that demand for precisely ground products like fine-pitch miniature taps makes innovative solutions such as this essential.

To reach the bottom of a 200-tpi thread form, the tip radius of the grinding wheel must be 20m to 25m (0.0008 " to 0.001 ") wide. In the past, people would always ask us to help them grind threads under a 0.005 " tip radius, and wed all duck and hide, Hitchiner said. There just wasnt a good answer. A lot of it was because of grinding machines with vibration issues.

Previously, superfine threads were ground with fine-grain conventional wheels. You needed a grain size that fit into the radius of the thread, Hitchiner said. However, standard fine-grain abrasives are from 220 to 400 mesh, 40m to 50m in size. Wheels employing such fine grains were unable to remove material quickly due to excessive wear, insufficient chip room and high tool pressure.

The solution was dressing the abrasive grains themselves to size. When dressing wheels to grind fine threads in HSS, Saint-Gobain found that a dresser could be applied to the two sides of the wheel that taper to form the grinding point. At the wheel tip, the dresser would cleave a coarse grain to produce the small tip radius required for a fine thread. The result was a large grain with the small radius ground into its tip. Most recently, weve done things to the grain of Saint-Gobains SG ceramic-alumina material that basically make it much easier to fracture it in this form, Hitchiner said.

A collateral issue is that dressing such a fine-tip radius requires a very sharp diamond-tipped dresser. The contact width of the dresser is critical, he said. The larger it is, the more pressure it puts on the wheel tip. You get to a certain point with the pressure, and it just snaps the tip off.

The challenge now, according to Hitchiner, is maximizing dresser life because a sharp dresser wears quickly. He noted that the process works well, but a more repeatable, sustainable dressing method would be welcome.

The diamond wheels applied to grind carbide forming taps added another challenge. You have a wheel that is going to wear a diamond dresser 20 times faster, Hitchiner said. He described a new Saint-Gobain diamond wheel bond technology, a proprietary nonvitrified hybrid material called Paradigm, which permits the use of an essentially flat CVD-diamond-based disc dresser to generate a 25m tip radius in a diamond wheel.

Compared to a diamond-tipped dresser, the disc dresser wears in a predictable fashion and enables high-speed dressing, which reduces cycle time for tap production by up to about two thirds. While grinding quality is essential, parts per hour is the key, Hitchiner said.

thread grinding - the pst group

thread grinding - the pst group

Thread grinding is a form of threading during which a CNC machine with an abrasive grinding wheel is used to cut the threads of the screw. Screws created through thread grinding are able to meet custom backlash requirements and tight tolerances.

Manufacturers may opt for thread grinding over thread rolling if using a high-hardness screw material, as some materials are too hard or brittle to allow for thread rolling. Thread grinding also allows for threads to be cut after the material has been heat-treated, or for threads to be cut on a complex design part.

While thread grinding is often less cost-effective than thread rolling, for many applications that need high degrees of accuracy or repeatability, ground ball screws are worth the additional costs in order to ensure the screw assembly is functioning properly.

As a trusted thread grinding partner, PST is proud to partner with organizations in a wide variety of industries. Machine accuracy and employee vigilance is critical at PST, and our inspection process ensures that each individual manufactured piece is produced to-spec.

PSTs thread grinding capabilities were put to work when manufacturer approached us after running into an issue with a prosthetic foot they were designing. Customers were complaining about the noise and clicking feeling in their joints, bringing unnecessary awareness to their prosthetic device. The problem was the screw thread that was acting as the Achilles tendon to lower and raise the individuals heel.

Contact Basic Contact Form Name First Last CompanyHow can we help you?Add your files here Drop files here or How should we get back to you?How should we get back to you?PhoneEmailEmail PhoneHow did you find us?Were a customerTradeshowCustomer ReferralWeb SearchWho referred you?CommentsThis field is for validation purposes and should be left unchanged.

all about thread grinding - precision tools and gage work processes

all about thread grinding - precision tools and gage work processes

Thread grinding may be utilized 1) because of the accuracy and finish obtained; 2) hardness of material to be threaded; and 3) economy in grinding certain classes of screw threads when using modern machines, wheels, and thread-grinding oils.

In some cases pre-cut threads are finished by grinding; but usually, threads are ground from the solid, being formed entirely by the grinding process. Examples of work include thread gages and taps of steel and tungsten carbide, hobs, worms, lead-screws, adjusting or traversing screws, alloy steel studs, etc. Grinding is applied to external, internal, straight, and tapering threads, and to various thread forms.

With single-edge or single-ribbed wheels it is possible to grind threads on gages to a degree of accuracy that requires but very little lapping to produce a so-called master thread gage. As far as lead is concerned, some thread grinding machine manufacturers guarantee to hold the lead within 0.0001 inch per inch (or mm per mm) of thread; and while it is not guaranteed that a higher degree of accuracy for lead is obtainable, it is known that threads have been ground to closer tolerances than this on the lead. Pitch diameter accuracies for either Class 3 or Class 4 fits are obtainable according to the grinding method used; with single-edge wheels, the thread angle can be ground to an accuracy of within two or three minutes in half the angle.

The wheels used for steel have an aluminous abrasive and, ordinarily, either a resinoid bond or a vitrified bond. The general rule is to use resinoid wheels when extreme tolerances are not required, and it is desirable to form the thread with a minimum number of passes, as in grinding threaded machine parts, such as studs, adjusting screws which are not calibrated, and for some classes of taps. Resinoid wheels, as a rule, will hold a fine edge longer than a vitrified wheel but they are more flexible and, consequently, less suitable for accurate work, especially when there is lateral grinding pressure that causes wheel deflection. Vitrified wheels are utilized for obtaining extreme accuracy in thread form and lead because they are very rigid and not easily deflected by side pressure in grinding. This rigidity is especially important in grinding pre-cut threads on such work as gages, taps and lead-screws. The progressive lead errors in long leadscrews, for example, might cause an increasing lateral pressure that would deflect a resinoid wheel. Vitrified wheels are also recommended for internal grinding.

Diamond Wheels: Diamond wheels set in a rubber or plastic bond are also used for thread grinding, especially for grinding threads in carbide materials and in other hardened alloys. Thread grinding is now being done successfully on a commercial basis on both taps and gages made from carbides. Gear hobs made from carbides have also been tested with successful results. Diamond wheels are dressed by means of silicon-carbide grinding wheels which travel past the diamond-wheel thread form at the angle required for the flanks of the thread to be ground. The action of the dressing wheels is, perhaps, best described as a scrubbing of the bond which holds the diamond grits. Obviously, the silicon-carbide wheels do not dress the diamonds, but they loosen the bond until the diamonds not wanted drop out.

With this type of wheel, the edge is trued to the cross-sectional shape of the thread groove. The wheel, when new, may have a diameter of 18 or 20 inches(45.7 or 50.8 cm) and, when grinding a thread, the wheel is inclined to align it with the thread groove. On some machines, lead variations are obtained by means of change-gears which transmit motion from the work-driving spindle to the leadscrew. Other machines are so designed that a lead-screw is selected to suit the lead of thread to be ground and transmits motion directly to the work-driving spindle.

The three-ribbed type of wheel has a roughing edge or rib which removes about two-thirds of the metal. This is followed by an intermediate rib which leaves about 0.005 inch(127 mm) for the third or finishing rib. The accuracy obtained with this triple-edge type compares with that of a single-edge wheel, which means that it may be used for the greatest accuracy obtainable in thread grinding.

The three-ribbed wheel is recommended not only for precision work but for grinding threads which are too long for the multi-ribbed wheel referred to later. It is also well adapted to tap grinding, because it is possible to dress a portion of the wheel adjacent to the finish rib for the purpose of grinding the outside diameter of the thread, as indicated in Fig. 1. Furthermore, the wheel can be dressed for grinding or relieving both crests and flanks at the same time.

This type of wheel is employed when rapid production is more important than extreme accuracy, which means that it is intended primarily for the grinding of duplicate parts in manufacturing. A wheel 1 to 2 inches(3.1755.08 cm) wide has formed upon its face a series of annular thread-shaped ridges (see Fig. 2); hence, if the length of the thread is not greater than the wheel width, a thread may be ground in one work revolution plus about one-half revolution for feeding in and withdrawing the wheel. The principle of operation is the same as that of thread milling with a multiple type cutter. This type of wheel is not inclined to the lead angle. To obtain a Class 3 fit, the lead angle should not exceed 4 degrees.

It is not practicable to use this form of wheel on thread pitches where the root is less than 0.007 inch(177.8 mm) wide, because of difficulties in wheel dressing. When this method can be applied, it is the fastest means known of producing threads in hardened materials. It is not recommended, however, that thread gages, taps, and work of this character be ground with multi-ribbed wheels. The single-ribbed wheel has a definite field for accurate, small-lot production.

It is necessary, in multi-ribbed grinding, to use more horsepower than is required for single-ribbed wheel grinding. Coarse threads, in particular, may require a wheel motor with two or three times more horsepower than would be necessary for grinding with a single-ribbed wheel.

The spacing of ribs on this type of wheel (Fig. 3) equals twice the pitch, so that during the first revolution every other thread groove section is being ground; consequently, about two and one-half work revolutions are required for grinding a complete thread, but the better distribution of cooling oil and resulting increase in work speeds makes this wheel very efficient. This alternate-type of wheel is adapted for grinding threads of fine pitch. Since these wheels cannot be tipped to the helix angle of the thread, they are not recommended for anything closer than Class 3 fits. The three-ribbed wheels referred to in a previous paragraph are also made in the alternate type for the finer pitches.

The process of forming threads entirely by grinding, or without preliminary cutting, is applied both in the manufacture of certain classes of threaded parts and also in the production of precision tools, such as taps and thread gages. For example, in airplane engine manufacture, certain parts are heat-treated and then the threads are ground from the solid, thus eliminating distortion. Minute cracks are sometimes found at the roots of threads that were cut and then hardened, or ground from the solid. Steel threads of coarse pitch that are to be surface hardened, may be rough threaded by cutting, then hardened and finally corrected by grinding. Many ground thread taps are produced by grinding from the solid after heat-treatment. Hardening high-speed steel taps before the thread is formed will ensure there are no narrow or delicate crests to interfere with the application of the high temperature required for uniform hardness and the best steel structure.

The number of cuts or passes for grinding from the solid depends upon the type of wheel and accuracy required. In general, threads of 12 or 14 per inch and finer may be ground in one pass of a single-edge wheel unless the unwrapped thread length is much greater than normal. Unwrapped length = pitch circumference total number of thread turns, approximately. For example, a thread gage 1 inches long with 24 threads per inch would have an unwrapped length equal to 30 pitch circumference. (If more convenient, outside circumference may be used instead of pitch circumference.) Assume that there are 6 or 7 feet of unwrapped length on a screw thread having 12 threads per inch. In this case, one pass might be sufficient for a Class 3 fit, whereas two passes might be recommended for a Class 4 fit. When two passes are required, too deep a roughing cut may break down the narrow edge of the wheel. To prevent this, try a roughing cut depth equal to about two-thirds the total thread depth, thus leaving one-third for the finishing cut.

When a screw thread, on the side being ground, is moving upward or against the grinding wheel rotation, less heat is generated and the grinding operation is more efficient than when wheel and work are moving in the same direction on the grinding side; however, to avoid running a machine idle during its return stroke, many screw threads are ground during both the forward and return traversing movements, by reversing the work rotation at the end of the forward stroke. For this reason, thread grinders generally are equipped so that both forward and return work speeds may be changed; they may also be designed to accelerate the return movement when grinding in one direction only.

Wheel speeds should always be limited to the maximum specified on the wheel by the manufacturer. According to the American National Standard Safety Code, resinoid and vitrified wheels are limited to 12,000 surface feet per minute(3657 m/min); however, according to Norton Co., the most efficient speeds are from 9,000 to 10,000(27433048 m/min) for resinoid wheels and 7,500 to 9,500(22862896 m/min) for vitrified wheels. Only tested wheels recommended by the wheel manufacturer should be used. After a suitable surface speed has been established, it should be maintained by increasing the rpm of the wheel, as the latter is reduced in diameter by wear.

Since thread grinding wheels work close to the limit of their stock-removing capacity, some adjustment of the wheel or work speed may be required to get the best results. If the wheel speed is too slow for a given job and excessive heat is generated, try an increase in speed, assuming that such increase is within the safety limits. If the wheel is too soft and the edge wears excessively, again an increase in wheel speed will give the effect of a harder wheel and result in better form-retaining qualities.

The work speed usually ranges from 3 to 10 fpm(0.93.0 m/min). In grinding with a comparatively heavy feed, and a mininum number of passes, the speed may not exceed 2 or 3 fpm(0.760.9 m/min). If very light feeds are employed, as in grinding hardened high-speed steel, the work speed may be much higher than 3 fpm(0.9 m/min) and should be determined by test. If excessive heat is generated by removing stock too rapidly, a work speed reduction is one remedy. If a wheel is working below its normal capacity, an increase in work speed would prevent dulling of the grains and reduce the tendency to heat or burn the work. An increase in work speed and reduction in feed may also be employed to prevent burning while grinding hardened steel.

Thread grinding wheels are trued to maintain both the required thread form and an efficient grinding surface. Thread grinders ordinarily are equipped with precision truing devices which function automatically. One type automatically dresses the wheel and also compensates for the slight amount removed in dressing, thus automatically maintaining size control of the work. While truing the wheel, a small amount of grinding oil should be used to reduce diamond wear. Light truing cuts are advisable, especially in truing resinoid wheels which may be deflected by excessive truing pressure. A master former for controlling the path followed by the truing diamond may require a modified profile to prevent distortion of the thread form, especially when the lead angles are comparatively large. Such modification usually is not required for 60-degree threads when the pitches for a given diameter are standard because then the resulting lead angles are less than 4 degrees. In grinding Acme threads or 29-degree worm threads having lead angles greater than 4 or 5 degrees, modified formers may be required to prevent a bulge in the thread profile. The highest point of this bulge is approximately at the pitch line. A bulge of about 0.001 inch(25.4 mm) may be within allowable limits on some commercial worms but precision worms for gear hobbers, etc., require straight flanks in the axial plane.

Crushing Method: Thread grinding wheels are also dressed or formed by the crushing method, which is used in connection with some types of thread grinding machines. When this method is used, the annular ridge or ridges on the wheel are formed by a hardened steel cylindrical dresser or crusher. The crusher has a series of smooth annular ridges which are shaped and spaced like the thread that is to be ground. During the wheel dressing operation, the crusher is positively driven instead of the grinding wheel, and the ridges on the wheel face are formed by the rotating crusher being forced inward.

Wheel hardness or grade selection is based upon a compromise between efficient cutting and durability of the grinding edge. Grade selection depends on the bond and the character of the work. The following general recommendations are based upon Norton grading.

Vitrified wheels usually range from J to M, and resinoid wheels from R to U. For heat-treated screws or studs and the Unified Standard Thread, try the following. For 8 to 12 threads per inch, grade S resinoid wheel; for 14 to 20 threads per inch, grade T resinoid; for 24 threads per inch and finer, grades T or U resinoid. For high-speed steel taps 4 to 12 threads per inch, grade J vitrified or S resinoid; 14 to 20 threads per inch, grade K vitrified or T resinoid; 24 to 36 threads per inch, grade M vitrified or T resinoid.

A thread grinding wheel usually operates close to its maximum stock-removing capacity, and the narrow edge which forms the root of the thread is the most vulnerable part. In grain selection, the general rule is to use the coarsest grained wheel that will hold its form while grinding a reasonable amount of work. Pitch of thread and quality of finish are two governing factors. Thus, to obtain an exceptionally fine finish, the grain size might be smaller than is needed to retain the edge profile. The usual grain sizes range from 120 to 150. For heat-treated screws and studs with Unified Standard Threads, 100 to 180 is the usual range. For precision screw threads of very fine pitch, the grain size may range from 220 to 320. For high-speed steel taps, the usual range is from 150 to 180 for Unified Standard Threads, and from 80 to 150 for pre-cut Acme threads.

Screw threads may be ground from the solid by the centerless method. A centerless thread grinder is similar in its operating principle to a centerless grinder designed for general work, in that it has a grinding wheel, a regulating or feed wheel (with speed adjustments), and a work-rest. Adjustments are provided to accommodate work of different sizes and for varying the rates of feed. The grinding wheel is a multi-ribbed type, being a series of annular ridges across the face. These ridges conform in pitch and profile with the thread to be ground. The grinding wheel is inclined to suit the helix or lead angle of the thread. In grinding threads on such work as socket type setscrews, the blanks are fed automatically and passed between the grinding and regulating wheels in a continuous stream. To illustrate production possibilities, hardened socket setscrews of -20 size may be ground from the solid at the rate of 60 to 70 per minute and with the wheel operating continuously for 8 hours without redressing. The lead errors of centerless ground screw threads may be limited to 0.0005 inch per inch (or mm per mm) or even less by reducing the production rate. The pitch diameter tolerances are within 0.0002 to 0.0003 inch(5.087.62 mm) of the basic size. The grain size for the wheel is selected with reference to the pitch of the thread, the following sizes being recommended: For 11 to 13 threads per inch, 150; for 16 threads per inch, 180; for 18 to 20 threads per inch, 220; for 24 to 28 threads per inch, 320; for 40 threads per inch, 400.

Centerless grinding is the grinding of cylindrical work without supporting it on centers in the usual way. Two abrasive wheels are mounted so that their peripheries face each other, one of the wheels having its axis so arranged that it can be swung out of parallel with the axis of the other wheel by varying amounts, as required. Between these two abrasive wheels is a work-supporting member equipped with suitable guides. The grinding wheel forces the work downward against the work-rest and also against the regulating wheel. The latter imparts a uniform rotation to the work which has the same peripheral speed as the regulating wheel, the speed of which is adjustable.

This article provided a review of thread grinding techniques, uses and applications, including the types of thread grinding wheels, speeds, hardness, and grades. Learn more about threads and threading from the Machinery's Handbook, 30th Edition, which is published and available from Industrial Press on Amazon.

Copyright 2021 Thomas Publishing Company. All Rights Reserved. See Terms and Conditions, Privacy Statement and California Do Not Track Notice. Website Last Modified July 10, 2021. Thomas Register and Thomas Regional are part of Thomasnet.com. Thomasnet Is A Registered Trademark Of Thomas Publishing Company.

grinding & thread rolling facility - aag auction

grinding & thread rolling facility - aag auction

AUCTION LOCATION: 11546 COLEY RIVER CIRCLE. FOUNTAIN VALLEY, CA AUCTION DATE: THURSDAY JUNE 3, 2021 @ 11:00 a.m. PST AUCTION PREVIEW: MORNINGS OF SALE: FROM 8:00 am to 11:00 am On-line bidding thru bidspotter.com Grinding & Thread Rolling Facility

FEATURING: Cincinnati OM Centerless Grinders **13-AVAILABLE** Cincinnati OM Centerless Grinding Machine w/ Hydraulic Grinding Wheel Dresser, Manual Feed Wheel Dresser, 21 Grinding Wheel, Belt Drive Conversion Cincinnati EA Centerless Grinding Machine w/ OM Conversion, Hydraulic Grinding Wheel Dresser, Manual Feed Wheel Dresser, 21 Grinding Wheel, Belt Drive Conversion Amada HA-250 10 Automatic Hydraulic Horizontal Band Saw w/ Hydraulic Clamping and Feed Waterbury Farrell No. 30 Thread Rolling Machine Kent KTM-380 Vertical Mill J & L 14 Optical Comparator Clark C500-40 4000 Lb Cap LPG Forklift Toyota 42-3FGC25 5000 Lb. Cap LPG Forklift Ingersoll Rand 5Hp Air Compressor Zygo mdl. 1201B LTS Laser Micrometer

ALL TERMS AND CONDITIONS BEHIND THE BIDDERS CARD SUPPLIED WILL APPLY TO ALL AUCTION SALE ITEMS AND FOR ALL PRIVATE NEGOTIATIONS. BY PARTICIPATING AND BIDDING AT AUCTION YOU ARE LEGALLY BINDING A CONTRACT WITH THE AUCTION COMPANY. ALL INVOICES MUST BE PAID WITHIN 24 HOURS FROM AUCTION DATE. IT IS PROHIBITED TO BID ON ANY ITEM THAT CANNOT BE PAID IN FULL WITHIN 24 HOURS FROM AUCTION DATE. PAYMENTS MUST BE CASHIERS CHECK, WIRE TRANFER, OR LETTER OF GUARANTEE FROM BANK. ALL ITEMS MUST BE REMOVED BYJUNE 12, 2019, 3:00 PM (PST) NO LOADING OR PICK UP ON SATURDAY AND SUNDAY. NO LOADING BY AUCTIONEER OR SELLER. BUYERS PREMIUM WILL BE 15% AND 18% FOR ALL ONLINE BIDDING ON BIDSPOTTER.COM. AUCTIONEER IS NOT RESPONSIBLE FOR MIS IDENTIFICATION OF ANY EQUIPMENT OR ASSETS BEING SOLD AT AUCTION EITHER BY VERBAL OR WRITTEN. IT IS THE BUYERS RESPONSIBILTY TO INSPECT THE GOODS AND ACCERTAIN IF THE SPECIFICATIONS, DESCRIPTIONS AND CONDITION OF THE GOODS CONFORM TO THE BUYERS REQUIREMENT INCLUDING SERIAL NUMBERS. BUYER ACKNOWLEDGES THAT THE EQUIPMENT OR ITEMS PURCHASES ONCE MAY HAVE CONTAINED, EXPOSED TO , AND OR UTILIZED HAZARDOUS MATERIAL. THERE MAY BE SURFACES ON ITEMS WHERE DECONTAMINATION CANNOT BE VALIDATED: AS SUCH, THE BUYER OR BIDDER ACKNOWLEDGING THAT THEY ARE ACCEPTING THIS EQUIPMENT OR ITEMS IN AN AS IS CONDITION. BUYER AND THEIR ASSOCIATES WILL HOLD AUCTIONEER HARMLESS AGAINST ANY AND ALL CLAIMS AND ACTIONS ARISING OUT OF THE PARTICIPATION OF THE INDEMNITEE IN THE ACTIVITY, INCUDING, WITHOUT LIMITATION, EXPENSES, JUDGEMENTS, FINES, SETTLEMENTS AND OTHER AMOUNTS INCURRED IN CONNECTION WITH ANY LIABLITY, SUIT, ACTION, LOSS, OR DAMAGE ARISING OR RESULTING FROM THE INDEMNITEES PARTICIPATION IN THE AUCTION. ALL BIDDERS MUST ONLY USE MACHINERY MOVERS WITH LIABILITTY INSURANCE OF $2,000,000 OR HIGHER. NO ITEMS SHALL BE REMOVED UNLESS PAID IN FULL AND ALL ITEMS SHALL BE REMOVED IN THE TIME ALLOCATED BY THE AUCTIONEER. ALL SALES ARE FINAL, AND ALL ITEMS ARE SOLD AS IS WHERE IS, WITH ALL FAULTS AND DEFECTS. THERE ARE NO GUARANTEE OR WARRANTY TO ANY ITEMS SOLD (RE: MAKE, MODEL, YEAR, HOURS, MILES, OR MERCHANTABLITY BY AUCTIONEER OR SELLER). BUYERS RESPONSIBILTY TO INSURE PROPER USE FOR SAFETY. ALL ITEMS ARE SOLD AS PARTS ONLY BUYER ACKNOWLEDES THAT THE GOODS ARE PRE-OWNED AND GOODS WERE EITHER DESIGNED NOR MANUFACTURED BY SELLER. SELLER HAS NO KNOWLEDGE OF OR CONTROL OVER THE PRIOR USE OR MISUSE OF THE GOODS OR ANY MODIFICATIONS TO THE GOODS FOLLOWING ORIGINAL MANUFACURER. NEITHER DOES SELLER HAVE KNOWLEDGE OR CONTROL OVER THE APPLICATION OF THE GOODS BY BUYER. IT IS THE BUYERS SOLE RESPONSIBILITY TO PROVIDE PROPER SAFETY DEVICES, EQUIPMENT AND INSTRUCTIONS FOR ANY PARTICULAR USE OR TAKE NECESSARY STEPS TO CONFORM THE GOODS AND OPERATION THEREOF TO ALL FEDERAL, STATE OR LOCAL GOVERNMENT SAFETY STANDARDS AND LAWS INCLUDING WITHOUT LIMITATION THE OCCUPATIONAL SAFETY AND HEALTH ACT OF OSHA. ANNOUNCEMENTS MADE BY THE AUCTIONEER ON THE DAY OF THE AUCTION TAKE PRECEDENCE OVER ANY PREVIOUS PRINTED MATERIAL PERTAINING TO THIS AUCTION. AUCTIONEER RESERVES THE RIGHT TO REMOVE OR ADD TO ANY AUCTION ITEMS ON THE LIST UNTIL AUCTION TIME.

TERMS OF SALE: CASH OR CASHIERS CHECK ONLY. 15% BUYERS PREMIUM ON ALL PURCHASES. $200.00 REFUNDABLE CASH DEPOSIT. 25% CASH DEPOSIT TOWARDS ALL PURCHASES. ALL SALES ARE SUBJECT TO CALIFORNIA SALES TAX. THERE WILL BE NO EXCEPTIONS.

how it works precision thread rolling | todays machining world

how it works precision thread rolling | todays machining world

At Horst Engineering & Manufacturing Co., one year old multi-axis Citizen Swiss turning centers and Eurotech multi-axis lathes pump out complete high precision machined components. They turn, they drill, they mill, and they even thread. Yet, in the same small East Hartford, Connecticut factory, Horst Engineerings sister company, Thread Rolling Inc., uses fifty-year old Waterbury, Hartford, and Reed roll threaders to form external threads with a specialized, yet elegantly simple, secondary process. Not all of their machines are antiques. Much of the equipment has been refurbished, and newer machines are mixed in with old. So it is fitting that they make their home in the most historic section of the old factory, where a fifty-five year old wood block floor symbolizes the sixty-year old family business.

Thread rolling is a process that has been around for more than one hundred years and there are machines in service that make the fifty-year old ones look young by comparison. Thread rollers come in a variety of types and sizes, but they all use a mechanism where hardened steel dies are matched and set to penetrate with force in order to reshape the material surface of a round diameter into a thread form. A cylindrical work piece or blank is fed into the machine (manually or automatically) and the dies rotate (cylindrical dies) or reciprocate (flat dies) in order to produce threads in a chipless forming process. Every thread form, shape, and size has a unique set of dies which are typically ground from heat treated tool steel (typically Rockwell C 58-62) and procured, rather than made in-house.

Thread rolling is primarily a cold forming process done at room temperature, but a niche does exist for hot rolling when materials are greater than Rockwell C 45, because die life would be seriously compromised. Like centerless grinding, its sister process, the thread rolling process can be in-feed or thru-feed. Thread rolling is the method of choice for high-volume production threading applications. Planetary die roll threaders are capable of forming threads on tens of thousands of parts per hour. High speed vertical or inclined flat die reciprocating machines can also generate high production rates, and horizontal cylindrical two die machines can quickly produce thousands of feet of threaded rod.

A lot of the stuff you get at the local hardware store, like wood screws, lag bolts, and machine screws, were mass produced with the help of thread rolling machines. Acme, buttress, worm, square, and pipe threads are just a handful of unique forms which can be produced by thread rolling; however, machine screw type threads are the most familiar to people in the precision machining industry.

On one end of the spectrum, high-volume automated thread rolling is interesting because of the speed and dimensional stability of the process, but the production of commercial grade fasteners and parts is a relatively ordinary practice. On the other end of the spectrum, there is the very specialized niche of high precision thread rolling, primarily on small batches of parts. Some high technology industries, including aerospace and motorsports, require extremely tight tolerance threads with super surface finishes, and the extra strength inherent in parts made with the forming process. Thread Rolling Inc. uses a combination of vertical cylindrical three-die machines, horizontal flat die reciprocating machines, and horizontal cylindrical two-die machines to produce precision threads.

The focus is on producing the high precision variety of machine screw style threads, concentrating on the standard 60 unified and metric thread forms most common to the aerospace industry. The most common threads rolled here are Class 2A and Class 3A in UNF, UNC, UNJF, and UNJC forms. J form threads have a larger controlled root radius for added strength in the high stress area of a thread and are common to the aerospace industry. Dimensional inspection of high quality threads is different from the commercial variety. Specifications vary, but aerospace and military standards require that indicating type thread gauging be used to inspect the pitch diameter and associated dimensions.

Inspection of pitch diameters are performed with both full form and single element indicating type gauges that are set with thread masters. Thread go/no go ring gages are used for reference only. Standard outside diameter micrometers are used for inspecting major diameters, and optical comparators are used to check minor diameters and root radii. With all of these gauges available on the shop floor, a thread rolling operator can monitor the process and make adjustments quickly. Die wear and other variables can affect the rolling process, but once a machine is set, the process is consistent and repeatable.

Formed threads are preferred for high strength and critical applications like those found in the aerospace industry. Threads that are rolled, especially on heat treated parts, have higher tension, shear, and fatigue strength. No material is removed during the rolling process, eliminating one of the inherent weaknesses of cut or ground threads. The cold formed properties include a higher density of material grains, or molecules, especially where they have been compacted along the lower flank of each thread pitch and in the root of the thread.

Aerospace metals can be difficult to machine and form, so the common threading attachments used on screw machines and lathes for higher volume work struggle to meet the quality requirements of precision threads. The force required to form threads on heat treated alloy steel or on exotic alloy parts made from Inconel or Titanium cannot be achieved effectively without using dedicated equipment. Thread Rolling Inc. focuses on threads that are less than 1.500 inches in diameter, but rolled threads are produced on fasteners up to 5.00 inches and even larger. It takes serious force, up to thirty or forty tons of rolling pressure generated by very large machines, in order to move that much material. Some threads are deemed so critical that a destructive testing sampling process is required to microscopically examine each pitch of a thread at 500X.

Properly formed threads require that the dies are exactly lined up, or matched. Whether the process uses two or three dies, they must track properly in order to avoid internal defects, such as overlaps, cracks, folds, seams, and craters. The destructive thread inspection method is used to identify internal defects and to verify that the proper material grainflow has been achieved. Representative samples are tested at the beginning of each new set up, and periodically during the course of a production run.

The testing process requires that the threads are cut from the rest of the part, bisected longitudinally, mounted in an epoxy resin, ground and lapped to a three micron finish, etched to reveal the micro structure, and microscopically inspected. The whole process takes a little more than an hour, but requires specialized metallographic preparation and inspection equipment. Because production pauses for testing, a range of machines are required, so the machinists work on several jobs at the same time, alternating between grinding, threading, and testing processes.

Many times, parts are received for service in bulk packaging, but when they are returned with shiny precision threads, they are individually packaged with protectors to prevent damage during shipment. On one recent day, a clerk was packing up a single blue container that was lined with padded foam.

The foam insert was die cut for a single prototype shaft. This eighteen inch part was thread rolled on both ends. The part had been designed and engineered to accommodate rolled threads. That meant that the pre-roll thread diameters were properly chamfered and ground to the correct pitch diameter, a hypothetical diameter in between the major and minor diameters, which is used to determine thread size. This particular job did not require destructive testing, but set-u pieces were produced from similar material in order to get the machines set. With a one-piece lot size, there is no room for error, and the highly skilled machinists knew this.

The highest quality rolled threads are produced from the best quality blanks. For that reason, most of the parts sent to Thread Rolling Inc. are left over-sized so that the final sizing process can be controlled by centerless grinding. Once the correct size has been ground, typically by a threading associate and a grinding associate working together, the parts are ground to their final size within .0004 inch while holding roundness within .000050. Before thread rolling, the surface finish on the diameter is always better than 32 microinches. Thanks to the burnishing action of the dies, the finish after rolling, especially on the flanks, can be as good as 4 microinches, depending on the material and hardness. Finish is another reason for choosing rolling over other threading processes.

The lack of CNC controls on most equipment means that the process is not as user-friendly as screw machining, turning, or milling. It is difficult to explain to customers that the major diameter actually increases in size when rolled. Some do not want to believe that they can turn their blanks below the major diameter and that their parts will not be scrap. For example a .250-28 UNF-3A thread has a pitch diameter of .2268-.2243 and a major diameter of .2500-.2435. The blank size prior to roll threading will be near the maximum pitch diameter and the material displaced by the dies will form up to fall within the major diameter tolerance.

The folks at Thread Rolling Inc. frequently hear that customers have shied away from jobs requiring thread rolling because the process seems difficult, mysterious, or out of their control. The process is unique, but within the precision forming industry, there are many specialists at the craft. The process just cannot be done as easily as one might expect in todays environment where do it all multi-axis machines automatically perform their work. A lot of feel is necessary to be a successful thread rolling operator. High precision thread rolling is a hands-on niche process that is here to stay.

Thread rollers come in a variety of types and sizes, but they all use a mechanism where hardened steel dies are matched and set to penetrate with force in order to reshape the material surface of a round diameter into a thread form.Very impressive blog,i was just looking for it thank,I am author of Band Saw Milling Cutter Manufacturers of Milling cutters,Gear cutters,Gear hobs, Gear shaper cutters, Endmills, Reamer,broaches,Spline broaches,Taps, Special cutters,Form tools.band shaw millingcutters,bell type shaper cutter,circular thread rolling dies.TMI specialises in the manufacture of wide range of Milling Cutters,Gear Cutters,Drills, Endmills,Reamers, Toolbits, threading tools and custom tools for the industrial use.

understanding the thread grinding process | newsroom

understanding the thread grinding process | newsroom

Thread grinding is a method of creating screw threads that utilizes a CNC machine with an abrasive grinding wheel. Compared to other thread manufacturing processes, thread grinding can be used to create incredibly complex and highly accurate thread designs.

The thread grinding process is complex and may vary depending on the specific requirements of the product. As a trusted thread grinding expert, PST utilizes a tried-and-true method that ensures accuracy and quality for all end products.

The thread grinding process consists of several steps from programming to production. PSTs average part cycle time is 10 minutes for this process; however, it may range from as low as 30 seconds up to an hour depending on the parts parameters.

Before placing product into a thread grinding machine, the required parameters must first be entered. For a new job, CNC programming and set-up can take up to two hours. However, for repeat jobs, the set-up time is minimal since the parameters were previously loaded.

Dressing the wheel allows the thread grinding process to meet custom tolerances and material requirements. Harder materials require a coarser wheel while softer materials use a finer wheel. This step ensures that the manufactured parts are fragment-free.

PST has external thread grinding capabilities up to 42 in length and 12 in diameter. Threads are ground between centers within the machine; however, if necessary, different holding methods can be tooled and set-up.

PST can also grind parts longer than 42 in length if each part can fit through the thread grinders spindle. This process requires multiple setups which ultimately results in additional time and cost.

A notable benefit of the thread grinding process is that it allows thread forming in very hard or brittle materials, which negates any complications from post-thread heat treatment. The thread is ground in the materials final state, and this provides the best accuracy in thread manufacturing.

Machine accuracy and employee vigilance are critical at PST. When starting a thread grinding project, an associate verifies each individual manufactured piece until the machine consistently produces to-spec product. This process may involve several additional steps and pieces of equipment including:

PST is a trusted thread grinding partner to organizations in a wide variety of industries. From build-to-print to custom thread grinding, PST can address the needs and specifications for many applications.

grinding wheels

grinding wheels

General purpose grinding wheel for use on all metals. Smooth grinding action and fast removal rates with minimal contact pressure. Abrasive: Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlorinated fillers. Application: Surface grinding, edge grinding Recommendation for Use: Recommended for angle grinders of ...

General purpose grinding wheel for use on all metals. Smooth grinding action and fast removal rates with minimal contact pressure. Abrasive: Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlorinated fillers. Application: Surface grinding, edge grinding Recommendation for Use: Recommended for angle grinders of...

MAINFEATURES Premium Aluminum Oxide Manufactured without addition of ferrous, sulphurous or chlorinated fillers. Stainless steel (INOX) Provides optimum grinding results on high-powered angle grinders. 5/16 thick discsprovide additional strength and service life for heavy-duty applications. TYPICAL APPLICATIONS Weld grinding, surface grin...

Highly productive, long life grinding wheel for stainless steel (INOX) and high temperature alloys. Smooth grinding action and fast removal rates are achieved with minimal contact pressure. Also suitable for carbon steel and all ferrous metals. Abrasive: Premium Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlo...

Highly productive, long life grinding wheel for stainless steel (INOX) and high temperature alloys. Smooth grinding action and fast removal rates are achieved with minimal contact pressure. Also suitable for carbon steel and all ferrous metals. Abrasive: Premium Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlo...

Highly productive, long life grinding wheel for stainless steel (INOX) and high temperature alloys. Smooth grinding action and fast removal rates are achieved with minimal contact pressure. Also suitable for carbon steel and all ferrous metals. Abrasive: Premium Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlo...

Highly productive, long life grinding wheel for stainless steel (INOX) and high temperature alloys. Smooth grinding action and fast removal rates are achieved with minimal contact pressure. Also suitable for carbon steel and all ferrous metals. Abrasive: Premium Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlo...

Highly productive, long life grinding wheel for stainless steel (INOX) and high temperature alloys. Smooth grinding action and fast removal rates are achieved with minimal contact pressure. Also suitable for carbon steel and all ferrous metals. Abrasive: Premium Aluminum Oxide INOX: Manufactured without addition of ferrous, sulphurous or chlo...

Performance grinding wheel with tough Zirconia abrasive grain providing outstanding stock removal and very long tool life. Abrasive: Zirconia Alumina Workpiece Materials: Steel, cast iron (grey and nodular types) Application: Weld grinding, edge grinding Recommendation for Use: Provides optimum grinding results on high power pneumatic or el...

Performance grinding wheel with tough Zirconia abrasive grain providing outstanding stock removal and very long tool life. Abrasive: Zirconia Alumina Workpiece Materials: Steel, cast iron (grey and nodular types) Application: Weld grinding, edge grinding Recommendation for Use: Provides optimum grinding results on high power pneumatic or el...

The PFERD range of reinforced grinding wheels provides outstanding stock removal, handling convenience, and high cost-efficiency. Performance Line SG is PFERD's widest range of products, for use in industrial and professional trade applications. Performance grinding wheel provides good removal rates and long service life for reduced wheel change...

The PFERD range of reinforced grinding wheels provides outstanding stock removal, handling convenience, and high cost-efficiency. Performance Line SG is PFERD's widest range of products, for use in industrial and professional trade applications. Performance grinding wheel provides good removal rates and long service life for reduced wheel change...

Walter HP cup wheels are designed for rough grinding or snagging work. Each wheel has a deeply anchored wrap-around steel hub for maximum safety and long life. A 5/811 threaded arbor for SPIN-ON mounting reduces downtime for wheel changes and helps you finish your toughest grinding jobs faster. 13,300 max. rpm.

Walter HP cup wheels are designed for rough grinding or snagging work. Each wheel has a deeply anchored wrap-around steel hub for maximum safety and long life. A 5/811 threaded arbor for SPIN-ON mounting reduces downtime for wheel changes and helps you finish your toughest grinding jobs faster. 24 grit, 12,200 max. rpm.

HP XX incorporates the latest advances in abrasive grain, bonding and manufacturing technology to substantially lower your total grinding costs. With the longest life in our grinding wheel lineup and extremely aggressive material removal, HP XX&trade will allow you to achieve the lowest overall cost of grinding on steel. 13,300 max. rpm.

MAIN FEATURES More Flexibility Cool Grinding Diamond-Cut Pattern - High Removal High Stock Material in All Material Reduces Cost - One Step Finishing Solution Flat and Curved Surfaces - Best Handling TYPICAL APPLICATIONS Curved Surfaces Grinding Metals Without Gouging Removing Welds and Leaving a Smooth Finish WHY FLEXCUT? FLEXCUT, t...

Our mission is to make it as easy as possible for you to find the products you're looking for made by the most reliable brands in the industry. We're always adding new products and if you can't find what you're looking for, reach out to us and we'll do our best to help!

rolling threads has advantages |
 

 modern machine shop

rolling threads has advantages | modern machine shop

With macros and canned cycles resident in the CNC on most contemporary turning centers, single point turning of OD threads can seem like almost a default process decision. However, for numerous applications, OD thread rolling has inherent advantages as an alternative to cutting threads.

Because the blank material is plastically deformed by pressure in the thread rolling process, it should have a minimum elongation of 5 percent and a maximum tensile strength of 246,000 psi.

This illustration shows the difference in grain flow between a rolled thread, left, and a cut thread, right. Additional tensile strength and improved surface finish are inherent by-products of the thread rolling process.

OD thread machining is done primarily with the use of turningusing single point and form tools, and grindingusing single contact or formed wheels. Both of these metalcutting processes are used to remove material to create the desired thread geometry.

Another process available to shops is thread rolling. Thread rolling is not a metal cutting process. It does not remove metal to create the desired profile, but instead it forms the thread into a mirror image of a roller die.

Metalworking manufacturers are under competitive pressures like never before. Its no longer sufficient to make parts the way we always have. Increasingly, matching the best processing technique to a specific application can mean the difference between making money on a job or losing it. Margins are that tight.

To illustrate an alternative to thread turning and grinding, this article looks at the advantages and disadvantages of thread rolling on CNC turning centers. Application specifications and various types of thread rolling are discussed, with technical input from LMT-Fette (Cleveland, Ohio).

Generally speaking, materials that are best rolled are difficult to cut and vice versa. Thread rolling relies on the plasticity of the base materialits ability to deformto permanently imprint the shape of the rolls on the workpiece blank. Good plasticity in a material being cut usually results in a gummy chip formation and built-up edge on the tooling. Cast iron, for example does not have a proper flow characteristic and therefore would not be a candidate for thread rolling.

According to LMT-Fette, because the pressure of the rollers will plastically deform the material, it should have a minimum elongation factor of 5 percent and a maximum tensile yield strength of 246,000 psi. These figures vary with material types and the size of the major and secondary diameters.

In the thread rolling operation, a head carrying the rollers is presented axially, tangentially or radially to the workpiece. While each type of roller head operates on the same basic principle, different threading applications require different approaches to the workpiece blank. Details of the three thread rolling types are discussed later in this article.

Assuming the workpiece material meets the yield and flow requirements for rolling, the process offers several advantages over cutting threads. Compared to other production methods, rolled threads have improved physical properties. The cold working that takes place in the thread rolling process produces an increase in tensile strength and a better surface finish than is achieved with cutting operations.

As in most cold working operations, the metal matrix of the workpiece blank is initially compressed by the force of the die causing it to yield plastically and conform to the shape of the die. Thread rolling operates in much the same way. The form of the roller or rollers in the thread rolling head imparts the shape of the thread into the workpiece blank.

The compression of the parent material results in a work hardening condition from compressing the metal matrix. It creates fatigue resistance in the thread. This hardened condition is part of the process, so any subsequent heat treating of a rolled thread will have an annealing effect. Thread rolling should be done after heat treating. Turning or grinding on the other hand, whether in a green or hardened state, severs the metal matrix to create the desired shape and leaves the metal grain structure virtually intact.

Successful thread rolling is a function of several application parameters. Among them is the type of thread to be rolled, its major diameter, pitch and root depth. Additional thread rolling considerations involve the ductility and cold-flow properties of the blank material.

When a thread is rolled, the thread shape is imparted on the workpiece blank by moving the parent material. A key parameter of this movement is the depth or root of the thread. As the roller displaces the material that will become the root, it flows out of the root both radially and axially.

The position of the rollers holds the thread pitch diameter to a predetermined size so the displaced material actually lengthens the workpiece blank. Depending on the size and shape of the thread being rolled, material savings of 15 to 20 percent can be realized using thread rolling over turning or cutting. On a large production run, this can add up to a significant amount of stock.

Because of the close relationship between the outside diameter of the thread and the workpiece blank, it is critical that blank diameters be highly accurate. The material flow rate is calculated based on the specified blank diameter and variation. Either over or under this diameter will produce unacceptable threads.

Undersized material will not fully flow into the roller dies and will cause undersized threads. Oversized blanks will exert undue pressure on the rollers and head resulting in potential damage to the thread rolling unit.

Thread rolling success is determined in large part by the shape of the form to be produced. Most of the threads produced are made to the 60 degree Unified and similar standards, which are easily rolled. Most of the rollers used to produce these forms have relatively sharp crests, usually with radius edge to help the die penetrate the material. The angles of these threads, 30 degrees on each flank, provide the force to make the material flow axially and radially in a controlled and predictable manner.

Acme and worm threads can be rolled, but the relatively large amount of material displacement and the distance the material must move can cause flaking on the flanks. Rollability of these types of threads is improved by changing the threads root configuration from flat bottom to a radius. Thread rolling can also be applied to burnishing, knurling and, in some cases, swaging operations.

Depending on the type of machine and thread that needs to be manufactured, shops have several thread rolling configurations from which to choose. An axial thread roller moves from the tailstock end of the turning center, along the workpiece blank centerline, to create a thread. General working ranges for axial heads are from 0.06 to 9 inches in diameter.

The axial head is usually mounted in one of the turning centers turret tool pockets. In one pass, three (or up to six) rollers are fed onto the blank and activated by the rotation of the workpiece blank.

The arrangement of the rollers on an axial head allows the blank to pass through, which enables threads that are longer than the roller width to be formed. The first few threads on these heads are progressive, like a tap or broach, and require a chamfer on the workpiece blank. Shorter progressions can be used for work up to shoulders or other workpiece features, but roller life can be affected by the additional stress.

As the name implies, the tangential roller head makes its threads by approaching the workpiece blank from the side. Sometimes called side rolling or cross slide heads, tangential thread roller are designed to roll threads by pushing, at a controlled feed rate, two fixed parallel rolls onto the rotating component. Mechanical or servo feed is required for tangential thread rolling. It is not possible to operate these rollers manually.

The rolls make square, tangential contact with the workpiece blank diameter forcing the material to plastically flow uniformly, taking the shape of the roller dies. This forming process is very fast and produces a precision profile, which is burr free.

In operation, the tangential roller will produce a complete thread in 15 to 30 revolutions of the workpiece blank. An advantage of this thread roller type is it can form threads very close (within one thread or sometimes less) to either the front or back of a shoulder or other workpiece feature.

Tangential rollers only roll threads within the width of the rollers. Working width ranges for Fettes tangential rolls are from 0.61 to 1.59 inches. These rollers are not recommended for Acme and trapezoid threads because force required is beyond the design limits of the holders.

The rolls on this type of thread roller are ground eccentrically. Starting with a flat on each roll, the thread form is progressive. A shallow thread form starts at one side of the flat and full form at the other side.

A three roll radial head at rest uses the aligned flats to create a clearance opening. This allows the workpiece blank to be positioned between the rolls and the finished threaded part to exit without damage to the threads. The two roll head uses the same principle.

Internally, the rolls are set in motion by releasing tension springs attached to a rotating clutch. Once released, the rotation of the workpiece or the roller unit continues the forward motion of the eccentric rolls until the torque of the workpiece blank resets the clutch spring.

Accurate and precise machining of threads is a key skill set for any shop. Considering thread rolling as a potential tool for the manufacture of threaded parts should be among a shops processing strategies.

Thread rolling requires a tooling investment to be made in the heads and rollers, which is higher than a single-point threading insert. However, for applications that involve hardened material, high surface finish and surface integrity as wells as production volumes, thread rolling technology may be more cost effective over the long haul. Moreover, since the heads can be run on a CNC turning center alongside single point threading, thread rolling can be flexibly applied as needed by the applicationthe right tool for the job.

One of the most common methods of tapping in use today on CNC machines is 'rigid tapping' or 'synchronous feed tapping.' A rigid tapping cycle synchronizes the machine spindle rotation and feed to match a specific thread pitch. Since the feed into the hole is synchronized, in theory a solid holder without any tension-compression can be used.

pferd 61001 ps forte 4-1/2

pferd 61001 ps forte 4-1/2"x1/4"x5/8" 11 thread grinding wheel

Our mission is to make it as easy as possible for you to find the products you're looking for made by the most reliable brands in the industry. We're always adding new products and if you can't find what you're looking for, reach out to us and we'll do our best to help!

thread grinding in northern ohio (oh) on

thread grinding in northern ohio (oh) on

Custom machining & finishing services including thread grinding for precision machined parts & components. Parts & components such as augers, feed screws, shafts, thread connectors, helical shapes & cylindrical parts can be handled. Grinding capabilities include external/OD grinding, internal/ID grinding, CNC grinding & multiple diameter grinding. Materials such as alloy steel, aluminum, stainless steel, bronze, cast iron, tool steel, Inconel, Monel, titanium & Hastelloy are used. Capabilities also include design-engineering, prototyping, machining, milling & CNC turning. Services are ISO compliant.

Thread grinding services for stainless steel, nickel, nickel alloy, Hastelloy, Inconel, Monel and other materials. Capable of handling parts up to +/-0.005 in. tolerance and 0.5 in. to 6 in. OD. Other capabilities include cutting, drilling, knurling, milling, turning and tapping. Designing and programming additional services provided. Prototype and low volume production offered. Aerospace, automotive, chemical, dental, electrical, food and beverage, laboratory, marine, military and mining industries served. Blanket orders and AutoCAD files accepted. Rush and emergency services available. Meets ANSI, ASME, ASTM, AWS and SAE standards. RoHS compliant. NADCAP certified. JIT delivery.

Stainless steel Swiss type centerless angioplasty wire grinding services for the medical industry. Materials machined include tungsten, titanium, Nitinol, molybdenum, fiberglass and exotic alloys. Capable of grinding parts up to +/-0.00005 in. dia. tolerance and finishes up to 4 Ra.

ISO 9001:2008 certified lean manufacturing capable internal/external thread grinding services of components & assemblies. Surface grinding & cylindrical grinding services are also available. Materials handled include brass, aluminum, mild steel, ductile iron, copper, bronze alloys, stainless steel, aluminum, steel sheeting, ABS, Delrin, acetal, Acrylic, nylon, PTFE, polyetheretherketone (PEEK) & glass filled plastic polymers. Hose assemblies, control module builds, O-rings, connectors, valve components, special fasteners, English to metric adapters, check valves, orthopedic instruments, pneumatic/hydraulic manifolds, hydraulic hose ends, crimpers & cylinders can be fabricated.

Precision grinding services including thread grinding, surface grinding, jig grinding, internal & inside diameter grinding, external & outside diameter grinding. Machined parts can be ground up to diameters of 12 in OD & 14 in. ID, lengths of 48 in. OD, 8 in. ID, tolerances of 0.0001 in., finishes of 2 micro OD & micro ID. Capabilities include grinding multiple diameters, angles, tapers, & radii.

Specializing in ID & OD thread grinding, CNC grinding, CNC cylindrical grinding & CNC thread grinding. Capabilities include grinding 60 in. of continuous thread & unlimited pitch ranges. Also includes precision lead screws, worm shafts with unlimited pressure angles & in-house machining service

Custom manufacturer of precision machined components for defense, energy, aerospace, military, industrial and government sectors. Capabilities include CNC machining, deep hole drilling, prototyping, EDM, CNC milling and turning services. Materials handled include titanium, Invar, Inconel, and Monel.

ISO 9001:2008 registered, Woman and Veteran Owned company. Manufacturer of standard and custom precision machined parts for the plumbing, automotive, heavy truck, HVAC, tube fabrication, hydraulic fitting and munitions industries. Products include fasteners, screws, nuts and sleeves. Materials used include aluminum, brass, stainless steel, leaded and non-leaded bar stock. Capabilities include CNC machining, prototyping, lathe work, sawing and turning. Services include EDM, assembly, warehousing, plating, grinding, brazing, drilling, milling, tapping, broaching, staking and crimping. Prototype to low volume production capabilities. Lean manufacturing capable. Kan Ban, dock-to-stock and vendor managed inventory (VMI) programs available. NSF approved.

Copyright 2021 Thomas Publishing Company. All Rights Reserved. See Terms and Conditions, Privacy Statement and California Do Not Track Notice. Website Last Modified July 10, 2021. Thomas Register and Thomas Regional are part of Thomasnet.com. Thomasnet Is A Registered Trademark Of Thomas Publishing Company.

Get in Touch with Mechanic
Related Products
Recent Posts
  1. electric horizontal grinders 2500 kva

  2. disc grinding machine manufacturers kenya

  3. raymond laboratory raymondgrinding mill

  4. tire grinding machine %28md 280 in delhi

  5. dta mizoram diamond cup grinding wheel

  6. cost to set up a grinder in india

  7. raymonds grinding mill

  8. crushers mill for sale south africa

  9. taclk grinding machines

  10. raymond woolen mills ltd pitampura

  11. gold bow mill price in zimbabwe

  12. wheel 600 grinding

  13. small jaw crusher manufacturer

  14. rotary kiln calcined bauite mining crusher equipment

  15. red mill semolina flour

  16. s9 mining machine

  17. stone crushing equipment pex300*1300 fine output jaw crusher with 30-130 tons per hour capacity

  18. ball mill principle price

  19. stone crusher logo

  20. machinery rotary dryer