The ANSI standard for ACME screw threads provides for two classes of fit, "General Purpose (G)" and "Centralizing (C)". The General Purpose fit provides for clearance on the major diameter and minor diameter while the screw and nut contact interface takes place on the thread flanks. The Centralizing fit provides for the same thread flank contact while simultaneously contacting on the major diameters. For applications of purely axial loading, there is little difference between the two. Centralizing fits may be preferred for applications that have loads transverse to the screw axis because the transverse loads are partially supported by the thread major diameters that act as radial bearings.
Roton uses materials that provide the very best thread finish and combine good machinability with weldability. Listed here are our standard materials in which screws are available from stock. Other materials can be used for production runs (For a list of materials that roll well, consult table 30 of the Worm section.)
ACME, HI - LEAD, and TRAPEZOIDAL LEAD SCREWS 1 1/2 inches and smaller in diameter are made from low carbon steel (1018-1020). Diameters larger than 1 1/2 inches are made from medium carbon steel (1045 - 1050). All stainless steel screws are made from 300 series stainless.
TORQSPLINES LEAD SCREWS are available from stock in low carbon steel.
BALL SCREWS are available in wide variety of grades of steel. Please contact Roton Engineering for information on specific sizes.
Although all screw products are work hardened during the thread rolling process, they are readily machined. Carbide tooling is recommended for the best machined surface finish and fastest machining times. As with all other machining tasks, users are encouraged to experiment with speeds, feeds and tooling to obtain the desired results with the fastest machining times for the equipment being used. Production requirements should be run on rigid CNC machines capable of taking heavy cuts under high speeds and feeds. Threaded screw shafts provide an additional challenge as the cut is interrupted, however, with a little experimenting machining the roll threaded screw products offered in this catalog is usually not a problem.
Yes and No. Our quality assurance and manufacturing procedures require the use of extensive CAD/CAM methods. As a result, we do end machining only for volume orders. For short runs, your own shop or a local machine shop equipped with an appropriately sized lathe and mill can easily handle most end machining requirements. Frequently these facilities can work from sample hardware or a hand sketch without the engineering formality needed for a production shop like ours, and they can provide a more cost effective solution.
These product lines differ primarily in their lead to diameter ratios. A screw's lead is the distance the nut travels in one revolution of the screw. A screw's lead angle is a measure of the lead/diameter ratio (see the formulas in the Application Engineering section). ACMEs have the lowest leads for a given diameter with lead angles ranging from about 2 degrees to 5 degrees. HILEADs have intermediate lead angles ranging from 4 degrees to about 16 degrees, TORQSPLINE LEAD SCREWS have very large lead/diameter ratio with lead angles of 17 degrees to 40 degrees.
The primary benefits of ACME screws are; low cost, self-locking (will not backdrive), and high mechanical advantage. If your application calls for a self-locking screw, then the ACME series should be used. A self-locking screw will not turn the nut under a thrust load and a good rule of thumb for self-locking is to keep the lead angle under 5 degrees. If you have limited torque available and don't care about fast traverse rates, then ACMEs can be used. If cost is the primary concern, then ACMEs offer the best value.
HI - LEADs and TORQSPLINE LEAD SCREWs offer the advantage of higher leads. If your application requires a fast traverse rate, then HI - LEADs or TORSPLINE LEAD SCREWs should be used. Some HI - LEAD screws will backdrive under certain conditions and all TORSPLINEs will backdrive. If backdriving is required, then TORSPLINE LEAD SCREWs (or possibly BALL SCREWs) should be used. For more help with applications, contact Roton Application Engineering.
No. The ANSI standard for ACME screws applies to single start screws only. When using multiple start ACME screws it is good practice to purchase the screws and nuts from a single source to guarantee good fit-up and good performance. All Roton multiple start screws are made under the HI - LEAD or TORQSPLINE names and using these will guarantee users of long, trouble free service life and future interchangeability.
Galling occurs when two like metals rub against each other. As the metals heat up from friction, the molecules of each bind together, eventually causing failure as the surfaces weld together. The higher the speed and the higher the pressure, the more likely this is to occur. Galling can be avoided by good lubrication and by using bronze or plastic nuts in place of steel nuts. Steel nuts are appropriate for low duty cycles or when good lubrication can be supplied, otherwise, steel nuts running on steel screws should be avoided. For high duty cycles and limited lubrication, plastic and bronze nuts should be specified.
Yes and no. Not all sizes we produce are listed in the catalog and we have many other sizes available to OEMs for production quantities. Roton has an accumulation of over 25 years of tooling and engineering of special sizes, so, no matter how unusual your requirements, give us a call. Chances are we can produce it, however, if your quantities are limited the more economical choice is likely to be a standard catalog item. For example, if you have an old machine that uses a single 1 5/8 - 4 ACME screw and it needs replacing, it will be much less expensive to use a standard size 1 3/4 - 4 ACME and to replace both the screw and nut than make a one-off special of 1 5/8 - 4 size. Special screw sizes may have minimum quantity requirements again making the choice of standard, catalog products more economical. For questions on specials, contact Roton Sales or Application Engineering.
It depends on the type of screw, as follows:
ACME Screws: The Diameter, followed by a dash and the number of threads per inch, followed by the hand, and the length in inches. (e.g. ACME Screw 1 - 4, RH X 144" OAL is a 1 inch diameter, 4 threads per inch, right hand, by 144 inch overall length ACME Screw)
TRAPEZOIDAL Lead Screws: The Diameter (in mm), followed by an "X" and the lead (in mm), followed by the hand, and the length in inches. (e.g. TRAPEZOIDAL Lead Screw 20 x 4, RH X 144" OAL is a 20 mm diameter, 4 mm lead, right hand, by 144 inch overall length TRAPEZOIDAL Lead Screw)
HI - LEAD and TORQSPLINE Lead Screws: The Diameter, followed by a "X" and the lead in inches per revolution, followed by the hand, and the length in inches. (e.g. HILEAD Screw 1 X .500, RH X 72" OAL is a 1 inch diameter, .500 inch per rev. lead, right hand, by 72 inch overall length HI - LEAD Screw)
BALL SCREWS: The Diameter, followed by a "X" and the lead in inches per revolution, followed by the hand, and the length in inches. (e.g. BALL SCREW 1 X .250, RH X 72" OAL is a 1 inch diameter, .250 inch per rev. lead, right hand, by 72 inch overall length BALL SCREW) Note: for FREEWHEELING BALL SCREWS the lead is actually the "effective lead". See the FREEWHEELING BALL SCREWS section on pages 36 - 38 for more details.
Alloy 4140 Heat Treated is only beneficial in very specific situations and is commonly "over specified". This is mostly because it is a popular material for bolts and fastener threads. Many users specify Alloy 4140 HT with the goal of increasing the wear life of the screw, but most screws are used with bronze or plastic nuts and a sufficient hardness differential exists between these materials and all steels such that performance of the nut materials is not affected. Alloy 4140 HT is also specified in the belief that it will enhance the stiffness of the screw. However, the stiffness of the screw is a function of the modulus of elasticity, which is the same for all steels, so elastic deflection under load and column performance will be the same. If strength is a concern as it may be on parts for aerospace or other weight sensitive applications then alloys may be desirable, however, most strength applications are better solved by using a larger size carbon steel screw in place of a smaller but more expensive alloy screw material. Also for high temperature environments (above 700° F) Alloy 4140 HT provides superior service. For more detailed discussions about this topic, contact Roton Engineering.
This term is short for "ASTM Grade A193, B7". "ASTM" stands for American Society for Testing Materials, an organization that writes and maintains industry standards for materials. Their standard A193 covers bolting materials used primarily in high temperature applications. ACME screws can be made to this specification but at a high premium (See Question 10 above). Sometimes users specify this material believing that it guarantees a better product than standard materials. The product will be different but not necessarily better. For a review of your specifications to see if they fit your needs, contact Roton Application Engineering.
No. All screws are furnished with an oil dip finish. For corrosive environments, stainless steel screws should be considered. We do not recommend plating as the film thickness of the plating alters the screw and nut fit-up requiring special sizing prior to plating. Also, electrolytic plating methods will apply differing thicknesses of plating over the length of the screw. As the slenderness of the screw increases (high ratio of length to diameter) so will the difference in plating thickness - the so-called "dog-bone effect". Short screws, especially those that can be barrel plated can be supplied with plating if the proper precautions are followed. Should you decide to have your screws plated, it is important to find a source that has experience plating screw threads.
In theory yes but in practical terms no. Standard length nuts as offered in the catalog provide the best price/ performance ratio. Extra long nuts require special tooling and gauging to work properly. They often experience fit up problems, creating hot spots that can expand thermally under load and bind locally on the screw. If capacity is a concern, then larger diameters should be considered. Where special over-length nuts are required or where larger than standard nuts are used for mounting convenience, users should consider adapting standard nuts by boring out the worn threads to fit the exterior of the standard nut (see Figure 12 in the Taps section). Contact Roton Engineering before designing a special nut which is longer than twice the major diameter of the screw.