First pass different to subsequent passes

[stugrey]

Hello everyone,

I've got a strange problem, my first pass when cutting out a shape seems to be off by a small amount (x/y not z) but on all the subsequent passes it seems to recover and is fine. Would cutting too deep with the first pass cause this as a slight bow in the wood meant that more was cut in the first pass than the others.

Hope you can help.

Cheers,

Stu

[PaulD]

Is the first pass always off in the same direction? Take a light pass and see if the problem still exists. I wouldn't guess that the problem is in the slides because if there was slop in you x-y axis bearings I don't think it would matter if the cutter is buried in the wood or not. It would dig in and pull the slop no matter what. Could it be in the software program? I have seen stepper errors that caused things like this. Loose wiring was one such issue. The motor was losing it's signal causing a miscount, but that was intermittent and not just on the initial pass.

If you are using HSS cutters it is possible that you are getting some cutter deflection, especially if the cutter is dull. You could switch to a solid carbide cutter and see if the problem still exists. (don't blame me if you break the durn thing)

You could try to narrow down the problem by programing in some straight line cuts for each axis and see if the problem exists on just one axis. this would indicate something loose. Also if you programed in a circle cut you might see an egg shaped bias on one axis.

If the problem is with the cutter you are running too fast or too dull or too small of a cutter.

Just a few ideas, good luck.