Re: Backlash Fixes

Chris,

The spring idea works fine on my lathe for the same problem. Look
at this link for a picture.

http://www.dakeng.com/ltfaq.htm#4.6

"Since there always seems to be backlash in any acme thread type
arrangement, I skirted this issue by preloading the slide rather than
replacing the screw. By attaching a cable to the cross slide and
running it to a couple of 1 gallon paint cans over a pulley I managed
to make the results of the turning quite satisfactory - especially
during profiling cuts which require the tool to move forward and back
in X without lost motion. When I got tired of tripping over the
cable I built this little gem, which accomplishes the same thing with
a tension spring and sits under the way cover. Sorry if you have to
crane your neck to figure it out - unusual camera angle eh? "

Holds 0.0003" on a good afternoon, which is close enough in my
world... There's about 20 lb acting on the slide there, give or take
change.

Good luck with your project!

Yours,
Dave Kowalczyk
shameless plug --> http://www.dakeng.com

--- In CAD_CAM_EDM_DRO@y..., ccs@m... 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.
>
> There is no way a ballnut will fit, and I don't want to mill out the
> channel in the crosslide like I did on my bigger lathe. So far I
have
> two ideas.
>
> 1) Install a spring that will push the tool away from the work.
Using
> a fairly long one, the variation in force over half an inch of
travel
> won't be large. The total force can be quite large, as the stepper
> actually only has to retract the tool, never advance it. This seems
> like a simple fix (which could be suited to longer travel with some
> sort of constant force device) but I never hear of it being used.
>
> OR
>
> 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?
>
> Thanks for any ideas,
>
> Chris Stratton
> ccs@m...