Problem with diagonal distortion

[shobley]

I built a BlackToe machine several years ago, and until recently it's been just great.

I did a test cut of a 4" circle in 1/4" plywood - 2 flute spiral upcut bit, 5000RPM and 50ips feed. - 0.1" per pass.

The circle (which is far from round anyway) came out with a diagonal distortion. (See attached image when the circle is rotated 90 degrees in the hole)

I was wondering if the gantry has dropped out of true? I checked all the bearings, chains and sprockets for slippage, but nothing seems to be loose.

Anyone have any tests I could try to figure out what might be wrong?

I've had slippage problems before, they were quite easy to identify, but this is a new one on me.

Steve

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[ger21]

Any backlash, or flex in the machine will cause that. something is moving when it shouldn't be.

[shobley]

Thanks for the reply.

I've experienced backlash before and that usually shows up quite clearly on circular cuts, I would suspect that it's flexing somewhere then.
I'm going to try doing some tests with just a pen and see how true the shapes are.

[underthetire]

Is this a DC servo machine? Looks like typical axis speeds out of sync or "lag".

[shobley]

No this is a stepper system with Gecko drives.

[shobley]

So... quick update.

I'm half way through a complete strip down and rebuild. Nothing wrong so far, but the machine could probably use some TLC. Once it's back up and running I will try some more tests.