Re: Climb Milling

Buck,

Your message reminds me of yet another "gotcha" in IMPLEMENTING
software backlash comp.

What do ya do when the next axis reversal is a move LESS than the
backlash amount? Or a series of moves WITHIN the backlash amount of
the machine. Or even worse, a series of short moves in/out and around
the "backlash band". I've seen software backlash compensation
algorithms which would take your mind quiz and FAIL it!

BTW, with a sherline advocated "normal" backlash of .003, and CAM
generated toolpaths(often lots of short line segments), this is not
a "theoretical" question...

To answer the mind quiz: NO, backlash does not "add up". The
exception is what I mentioned above; i.e., a control which does not
implement compensation correctly CAN make the b/l "seem" to increase.

Hope this helps.

Ballendo

P.S. It would be a good idea to repeat your backlash measurement
routine at several locations along each axis; and also using
differing lengths besides one inch. And lastly, a drilled hole will
not be a good thing to measure to, on any but the most basic (and
likely low-resolution) machines.

--- In CAD_CAM_EDM_DRO@y..., yahoo@a... wrote:
> To Measure backlash:
> Travel one inch in the positive direction;
> Drill hole number one.
> Travel one more inch in the positive direction;
> Drill hole number two.
> Travel back 1/2 inch, in the negative direction;
> Drill hole number three.
> Hole three will not be 1/2 inch back from hole number two, by the
> backlash amount.
>
> Yes, it is used everytime a motor reverses direction. It applies to
> circles - everything.
> The motor runs an extra amount, equal to the backlash, for only the
> first move after each direction change.
>
> The extra motor movement is just "taking up the backlash".
>
> Backlash can be a combination of gaps and defections (under load).
> Gaps are symetrical, deflections may not be and defections are
> usually somewhat (nonlinear) force dependent.
>
> A mind quiz: If you have a back and forth moves, does the backlash
> accumulate? Or after 10 back and forths are you off from where you
> started by 10 times the backlash?
>
> Buck