setting up the CNC mill

A few weeks ago I built a hobby CNC mill from some sort of plastics. And fixing up steppers, controllers and start using TURBOCNC program which is running very good.

Because I don't have a scale micrometer to measure backlash, I built a simple 'instrument' to only show me backlash, not to measure it. It works well.

And I set appropriate value for backlash with this program

G91
G01 X+1
G01 X-1
M00 Set zero on my 'instrument'.
G01 X-1
G01 X+1
G90
M02 Get backlash with the smallest manual (jog) step in + direction until the 'instrument' show the zero and then read from program value of X axis

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





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