Re: [CAD_CAM_EDM_DRO] Re: No more backlash!

Alvaro Fogassa wrote:

>
> Ron, the lead screws that sherline uses are no better than 0.004" per
> foot,that's why they say on the instructions manual to set the
> backlash nut no tighter than .003", other wise the nuts won't last
> too long nor do the lead screws.
> Now,if you can get a lead screw with let's say,0.001" lead accuracy
> per foot than it might work.

Im not sure this is true. The spec of .004 per foot says the accuracy of
the thread may be that much off, but I suspect any one piece of rod has
a very constant pitch along its length, and thats what matters for any
screw to work with this kind of nut.

Note also the spec really says "no worse than" not "no better than", so
in fact a screw could be only 1 or 2 thou per foot off of true accuracy.
You are promised it will not be MORE than .004, and can be a lot less if
you are lucky.

With the stock Sherline nuts setting them to zero backlash would cause
excessive wear.

My X screw is very smooth along its entire length. The Y screw has a
slight drag on each rotation, so I think it may have had a very slight
bend in it when I cast the nuts. It is not perfect, bur well within
useable limits.

> As for the grizzly,well...,if the lead screws on sherline aren't
> that good,you guess it....
> The ones on my grizzly,was so tight that it would turn ok at the
> beggining but when it gets to the midle of the travel I've to use two
> hands to turn it. i'm shure it will turn easyer once the nuts wears
> out.anyway I'm not using the original screws any more.

I would look at the alignemnt of the nuts. On my Grizz the screw was
very well formed, and when the nut is run along the thread while removed
from the machine it is smooth along the entire length. I had a lot of
trouble getting the nuts installed to be smooth over the entire range.
If there is any error in their mounting the screw will be hard in some
regions. Wear will 'improve' this, but proper alignemnent would be
better.

I have not measured the Grizz screw, but again, I expect its pitch to be
very uniform along its length, but maybe not accurate.

ron

>