Re: [CAD_CAM_EDM_DRO] Skipping steps, avoiding resonance

Hi Randy,

I've had a number of similar problems with 3D contouring and lost steps
on a BP clone retrofit. In spite of a LOT of experimenting, I never was
able to resolve the mystery with my stepper motor setup but I have made
significant progress since converting the mill to servo motors. I still
don't understand why a stepper system wouldn't work - provided the
motors have sufficient reserve power etc., it should have worked! I was
running direct drive 1800 oz-in steppers with Geckos and Flashcut
software. I should point out it worked great for all my 2D and 2.5D
stuff. Some 3D contouring worked and some other files caused the
gradual loss of position - as you have described. With my steppers, I
was able to significantly reduce the problem by reducing feed rates to
say 6-12 inches per min - but that was unrealistic to actually get any
work done. I experimented with full step, half step and 10uSteps as the
G210 permits - I didn't observe any improvements one way or the other.

Reduce your accelerations and top speeds and see how that helps.

I converted to Servos and currently I'm evaluating the Rutex R990 servo
motor drives and a much bigger power supply (1500VA) but I'm still
tuning the PID parameters. My errors have diminished dramatically but
I've really only just started testing everything over the last few days
so I don't have a conclusive result. FYI, my g-code is created by the
full version of Visual Mill.

A couple other things to remember - you can't plunge a center cutting
end mill at the same rate you can side cut. If your plunge rate is too
high, you may be pushing the endmill up into the collet causing a loss
of position. Another thing, I was recently cutting 1/4" polycarbonate
sheet and machining down to .5mm material remaining in places and with
standard high helix endmills the material was lifting off the fixture
causing a scalloped surface. I went to a carbide side cutting endmill
(no helix) and now the flats are very smooth.

Sorry I don't have THE answer.

Cheers, Peter