[IAmJerico]

Hello!

We have a new retrofitted 3-axis CNC Milling Machine that uses a China-made breakout board for Mach 3. Everything's running smoothly as planned but here's the problem:

We have calibrated the steps per unit of my X and Y axis including backlash with a dial gauge so I guess it is right. However, when we try to run a simple program to test the machine, the product seems to have the wrong dimensions.

Example: A mild steel plate with a slot hole in the middle. The slot dimension is 10 mm wide x 50 mm length. I programmed it in Mastercam and then ran it. When the job finishes, the slot dimension goes from 10 x 50 to 9 x 48.

Any idea why this is happening?

I appreciate any help you can provide.

-Jerico

[joeavaerage]

Hi,
firstly there is no real programmatic solution to backlash. The feature that Mach uses it to 'take up' the lash, that is to say the 0.5mm or whatever you program in at each axis reversal.
This does not solve backlash, if it there it will show up under different circumstances. The only real cure for backlash is to upgrade to ballscrews with zero lash.

The most likely cause of dimensions drifting off like that is the steppers missing steps. Any high acceleration move, including the axis reversals commanded by the backlash module can produce missing steps.

Try reducing the accelerations, both regular Gcode and backlash by half and try again.

Craig