Re: [CAD_CAM_EDM_DRO] Preloading ball screws

>.I had been depending on rigid backlash adjustment by
>simply screwing one of the nuts tightly against the other, and tightening
>both setscrews. As I understand it, a spring type arrangement is more
>advantageous due to wear issues which act to change the fixed preload over
>time.

Bill,

I dont understand exactly what you are talking about. But, Ballscrews are generally precision assemblies that require no adjustment. Their manufacture is very precision. If a ballscrew develops backlash the balls or other components are worn. And that is generally after many years of usage. The type of configuraton you are describing is typical of acme thread backlash adjustment. If you have backlash I'd be looking at the ends of the ballscrew where they react with the table for freeplay (which can be corrected with shims) and the center union possibly being loose. Ballscrews can be disassembled and balls replaced but, you better have a lathe handy. You will need to make a special assembly tool as follows: Machine a sleeve, On the ballscrew measure from the bottom of the helical race on one side to the bottom of the helical race on the other side with calipers. This will be the O.D. of the sleeve. Then measure the shank diameter on the end of the ballscrew where the screw portion
begins and this will be the I.D. of the sleeve you are making. Now, measure the length of the ballnut and /or block in which it resides. Add 1" to it and this will be the length of the sleeve you are making. It takes patience to do this, Work over a white bath towel spread out in case you drop any balls, feed the sleeve in the end away from you of the ballnut just a little past the transfer tube (the tube that recirculates the balls, its visible on the outside and inside of the nut) most ballnuts have two tubes. With the sleeve in this position begin feeding the new balls (mic and count the old ones and Mcmaster Carr has them) into the race. Keep pushing them into the race with a small screwdriver until they exit the other end of the transfer tube. Now, begin pushing the sleeve thru (Dont spin it) and feeding balls as you go until it is full or close to it. if its a dual ball nut push the sleeve up to the next transfer tube and repeat the same procedure, be careful to not put
balls in the area between the two actual nut areas, a ball trapped in there would spell disaster. Now, with the ballnut loaded slide it over the shank of the ballsrew, being careful to keep the sleeve seated against the face where the ballscrew portion begins thru the entire assembly. Start rotationg the nut clockwise (providing its right hand thread) and it will feed itself on the screw and push out the sleeve as it goes, make sure you have it in the correct orientation to the machine. Wallah! back to new ballscrew. (or close to it)

Ron



Bill Kichman <billkichman@...> wrote:
I am sure this has been covered ad nauseum, but here goes...I have 2
ballnuts threaded into a steel block which is attached to my table for my
ballscrew conversion...
My question is this....as I have no room whatsoever on at least one of the
axes for adding anything to the periphery of the nut, and the threads
already are there, would it be reasonable to attach a strong spring such
that it would act to tighten the threaded ball nut's threads at all times?
That way, the spring wouldn't have to be nearly as strong as an installation
without the threads installed and a heavy spring arrrangement in-line with
the nut. Am I seeing this clearly? The spring could partially wrap around
the nut and keep a constant preload.
Has anybody done this?
R. William Kichman, P.E.
Kichman Engineering Associates
103 Old Furnace Road
Cornwall, PA 17016-0643
tel/fax 717/270-0714



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