Acme Screw Design Considerations
Mounting and Pinning of ACME Flange
Flanges must be secured to acme nuts. The preferred method of locking a flange to a nut is a pin or set screw parallel to the screw which intersects the flange/nut mounting thread. Because of the dissimilarity of materials, the hole may need to be milled, not drilled.
Alternatively, the flange may be drilled and tapped radially for a set screw. After assembly of the flange to the nut, spot drill the nut threads through the flange and install a dog point set screw from the flange O.D. into the nut O.D. threads. Avoid getting metal chips in the nut when drilling. (See Image 1 in Figure 1 Below for pin size).
|up to .625||1/8 x 1/4 Slotted Spring Pin||1|
|.75 to 1.0||#10 - 24 x 1/4 Set Screw||1|
|1.125 to 1.375||1/4 - 20 x 1/4 Set Screw||2|
|1.5 to 3.0||5/16 - 18 x 1/2 Set Screw||2|
|3.375||3/8 - 16 x 3/4 Set Screw||2|
|4+||1/2 x 13 x 1 Set Screw||2|
Commercially available thread adhesives may be used for light load applications. Follow the manufacturers' recommendations to ensure a satisfactory bond. Avoid getting the adhesive onto the acme screw thread.
Proper lubrication must be provided to achieve satisfactory service life. Nook PowerAc™ lubricant (E-100 spray lube or PAG-1 grease) is recommended for applications using PowerAc™ nuts.
Lubrication intervals are determined by the application. It is required that screw assemblies are lubricated often enough to maintain a film of lubricant on the screw.
Driving torque is the torque required to move a load and is calculated by multiplying the force needed by the "Torque to raise one lb" value listed in the technical data section for each screw and nut size.
EXAMPLE: To lift a 1,000 lb load using a 1" - 6 RH acme screw with plastic nut, 74 in lb of torque are required..074 in-lb/lb × 1000 lb = 74 in-lb
With proper lubrication, PowerAc™ Acme Screws with bronze nuts operate efficiently between 15°F and 350°F, and plastic nuts between 15°F and 175°F. Consult the factory for low temperature applications.
To obtain optimum performance of your acme screw assembly, it is recommended that the machining be performed at the Helix Linear Technologies factory. Screws may be purchased machined to your specifications or to standard end machining designs shown on pages 204-206 of our Precision Screw Assemblies Catalog.
Acme screws in operation generate an axial load and a radial load; therefore, end mounts must be designed to accommodate these loads. Helix Linear Technologies has designed precision end mounts to work specifically with acme screws. For a detailed description of these bearing supports, see pages 207-213. An EZZE-MOUNT™ can be shipped pre assembled to a PowerAc™ Acme Screw. For complete PowerAc™ Acme Screw Assemblies refer to pages 20-29.
Optional Surface Coatings
Consult Nook engineers for specific surface coatings for anti-corrosion and lubrication.
Boots and Bellows
For contaminated environments, use of a boot or metal cover to protect the acme screw assembly is recommended.Figure 1