Re: setting up the CNC mill

Boris:

Do you mean that if you execute G01 X-1 and G01 X+1 once it returns to
almost 1.000 but is off by some small delta, but if you repeat this many
times it drifts away from 1.000 a little more with each execution? If it
doesn't return to the same point after each loop it's more than a
backlash problem.

If this is the case it may be losing a step with each reversal + to - or
- to +. Jon Elson identified a similar lost step in my machine. I was
using EMC with an opto-isolator which inverted the signal.

You might run this loop many times, say 100, and measure the error in
returning to zero. If this is 100 times a single step (mine is .00025")
you're probably losing one step each loop. If double it could be two
steps, etc.

I had the same error in both X and Y and it was consistently one step
for each reversal in one direction. I tried a different controller and
the error went away. I then took out the opto-isolator and the error
went away with EMC. It was probably some wierd timing problem in EMC but
once I got it working I didn't try to isolate the problem further.

If this seems to match your problem try this. If not, never mind. :-)

On 28 Oct, Boris Maraž wrote:
> But I have a problem with repeating functions, which I can't resolve.
> If the program makes G01 X-1 and then G01 X+1 twenty times, with each
> move the mill go for more then 0.01mm in positive direction on X axis.
>
> Then I change program to get other direction backlash. I only change -
> to + and + to -. And the values are different from previous values.
>
> It is possible that the machine have different backlash for - and +
> direction on the same axis? How to correct this differences?
>
> Boris

Hugh Currin
Klamath Falls, OR