ACME thread vs. UNC threads

[steris]

I am designing a system to translate rotary motion from a motor to linear motion. For my application I can't use a rack/pinion or pulley/cable, the only thing that works is a screw gear arrangement.

I am looking at the trade-offs between using a ball-screw, ACME threaded rod with ACME nut or UNC threaded rod with UNC nut. I don't need precision or repeatability. I have a small load (only about 200 lbs). The same 6" of thread will be traversed up to 10x/day.

The ACME threads and ball screws are much too expensive especially since I don't need precision or large load capabilities. I am leaning towards using a UNC threaded rod with nut 2"-4 because of cost but I am worried about wear. Are there other options that offer decent wear resistance without high cost? Also is there anything I can do to minimize the binding between the nut & screw?

Any advise would be greatly appreciated! Thanks in advance!

Best,
-Steris

 

[drawoh]

MachinaMan,

Self locking is a function of lead angle. Thread profile is much less important.

JHG

 

[MachinaMan]

Hi drawoh,

I agree.

ACME threads are usually made as self-locking because they are a power screw. I still suggest checking for UNC because their use as a power screw is not what they were made for, therefore they won't necessarily be self-locking.

Thanks for clearing that up for me.

 

[drawoh]

MachinaMan,

Whether or not an ACME screw is designed to be self locking depends on the application. I might want to be able to rotate my screw with axial force.

A UNC screw had darn well better be self locking.

JHG

 

[plasgears]

Car seat actuators use acme threads routinely. Replacement parts from auto dealer stock may give you quick experience with this.

 

[hydtools]

RV trailer stabilizers use acme threads. Acme threads must not be too expensive.

Ted