Material recommendation for a smooth finish on ACME threads?

[pkelecy]

Hi All,

I'm working on a project where we plan to test a new low friction coating on an ACME lead screw and nut. To get the best performance (lowest friction) possible, the thread surfaces should as smooth as possible (to minimize any mechanical interlocking due to surface irregularities). Since we plan to have both the screw and nut fabricated for this, I was wondering what material to use (grade of steel or alloy) and/or heat treatment for this (for the smoothest finish via grinding, etc.) while still providing reasonable strength? The coating itself will provide a hard surface over the threads, so the wear properties of the material aren't as important as it's ability to allow a very smooth finishing to be formed.

Any recommendations or feedback on this are greatly appreciated. It's a new area for me.

Thanks,

Pat

[THE WURM]

If you are not concern with the material hardness try 12L14, it doesn't get much easier. Depending, the length of the thread and the tools will be significant factors.

[ViperTX]

Welcome pkelecy!

Why don't you just purchase a precision ACME screw, if all you are doing is surface material testing? Plus, I think you're chasing the dog's tail....ACME screws by their nature are suppose to oppose backdriving.

[RICHARD ZASTROW]

pkelecy You might want to check with the coating provider. They usually will give you the surface finish requirements etc. Also, ask if any alloying agents are a no-no. I'm not picking on 12L14, but it does contain lead. I had the same problem when I ordered an extremely low sulphur content in D2. Our purchasing agent got a deal on some other supplier's D2, it contained too much sulphur. Resulted in chipped die edges where sulphur puddled during heat treat & formed carbides. Sort of like measuring twice and cutting once.

[pkelecy]

Thanks for the replies, and the 12L14 material suggestion. I'll look into it.

I had originally looked into purchasing stock hardware for this, as someone suggested, but the issue was finding a suitable *steel* nut. Most lead screws use bronz or plastic nuts.

Also, and this is something I didn't mention, the nut needs to be cut in two (lenghwise) to expose its threads for plasma coating. The plan is to cut a whole nut in two, plasma coat each half, and then fit the halves in a cylindrical collar afterwards to hold them together. So I was hoping to find a steel nut with a flange on it (preferably machined into the nut body, not threaded) that could be use to locate the two halves in the collar. So far I haven't found any stock part that would work well for this. If you know of any, please let me know. But most screw manufacturers (i.e Nook, Roton) can make this pretty easily as a custom part, which is the plan at this point.

Thanks again for the help.