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Shot peening acme threads

pistonskirt

Hot Rolled
Joined
May 9, 2004
Location
Plymouth, Devon, England
Somewhere on this board I read a discussion about making replacement acme thread cross slide screws & the preference for a ground thread over a turned finish in terms of longevity of the feed nut.
I wonder if a lathe turned acme thread saturation shot peened would present a suitable finish for this application, the peening should effectively remove any tool marks with a possible additional benefit of the minute surface dimples providing lubricant reservoirs, with carefull choice of shot size & intensity dimensional changes should be minimal.

Any thoughts, comments, experience ?

regards

Brian
 
Precision rolled acme stock is your best bet. The finish is unbelievably slick, and its not too expensive. I've made a lot of cross and compound screws and nuts for one customer that has several large lathes that are 40+ years old, and the results are very good. I've used the 4140 rolled stock because its about Rc 28-32 and doesn't cost much more than the 1018 variety.
 
Shot peening a motion producing thread will raise edges of the minute craters above the load flanks. The effect would be to turn the screw into a lapping tool until the crater edges wore down.

Screw threads operate in mostly in boundary lubrication mode; the moecules thick trace of oil that attaches to the screw and nut. Here slick smooth surfaces are beneficial.

I really don't see shot peening as improvingthe performance or durability of Acme screw theads.
 
Thanks Metl, I was completely unaware that rolled acme stock was available, it sounds like a very practical & affordable solution to unavailable replacements for obsolete machines.

As usual Forrest your points make perfect sense, my thoughts were based on 20 years of using shot peening in completely different applications to good effect. Next time I am at the Metal Improvements Co I will ask the same question, the idea still intrigues me.

regards

Brian
 








 
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