CNC machine cutting incorrect dimensions

[Neale]

Wow - can't manage 1mm cut in acetal. That's an interesting testimonial to the machine...

[JAZZCNC]

Right, I believe you identified the problem: not enough machine stiffness!
I'm milling Delrin/Acetal with it and just tested it with a Z cut depth of 0.2mm instead of 1mm.

Nah you have some other issue that's causing this. While these machines are rubbish in lots of areas they are stiff enough to cut Acetal at 1mm DOC.

The reason you are not losing position now is the load is less and 0.2mm in plastic is almost like cutting fresh air. You need to find what's causing the lose of steps and the first place I'd look at is the motor tuning.!
Just for testing purposes lower the velocity for each axis by 50% and try cutting again at the 1mm Doc and see what happens.

Edit: Just spotted that the Motor tuning below is not yours so what is your tuning set at.? The figures in the tuning below are about where I would expect for this machine and why I said to only low velocity not acceleration as this is on the low side anyway. If your acceleration is much higher than this then lower that also by 50%.

[richie00boy]

I have cut anodised alloy at 0.5mm depth with those settings, so I agree with Jazz that you haven't fixed it yet!

[Clem]

I have cut anodised alloy at 0.5mm depth with those settings, so I agree with Jazz that you haven't fixed it yet!

Yeah after some more testing I agree with you as well... :-/
That wasn't the issue...

I've played around with the motor tuning (speed and acceleration), but it hasn't changed anything.

More testing to be done at the weekend, I guess... :-)