Re: [CAD_CAM_EDM_DRO] Backlash Fixes

ccs@... wrote:

> I'm trying to find a way to get zero backlash on a 9" south bend
> lathe, over a crosslide travel of about half an inch, in order to do
> some high precision taper work with a sort of single motor cnc taper
> attachment setup. Zero backlash is necessary because the stepper
> motor will be retracting the tool in the direction of cutting force.
> I should also mention that this is not a production setting - ie, it
> only needs to work for about an hour at a time, and some rebuilding
> between uses is acceptable.

I obtained a very small ballnut on eBay, 3/8" diameter, the nut OD is
about 1/2". I did look for a year before this came up. So, they do
exist. If you have an Acme screw that is unworn, you can tighten
up the nut, use two nuts with an adjusting mechanism, etc. to get
the backlash down to near zero.

I cut short tapers with the compound rest. I cut it close with pointed
tools, then mount the toolpost grinder and make a test pass. I check
the taper with bluing and a master arbor and then adjust the angle
until the bluing indicates the taper is a good match, and then grind to
final size.

> 2) Buy some new screw stock, obtain a loose fitting nut, and inject
> moglice (the teflon-matrix-epoxy bearing rebuilding material). I'd
> use new screw material to get consistent unworn threads, sacrificial
> material for any needed lapping, to be able to simply throw it away if
> I don't get the release agent right, and to maybe choose an ideal
> threadform. Anyone done this successfully? What would the ideal
> threadform for moglice be?

I have heard that several people have done this with good results.
Use LOTS of smoke for mold release agent. I have heard that the
minimum is siz layers of smoke. The Acme thread is fine.

I made a screw and matching nut for my last lathe. I got backlash
under .001" without adjustment.

Jon