If you would be moving very slowly when you first hit the metal, and only accelerate slowly when you are in the metal already, I think that would still count as “gradual” changes in load. At least for the X/Y steppers.
You might get a lot of vibration or chatter, but you may be able to average that out or something. I haven’t tried anything like this yet though, so I could easily be wrong.
I had one lying around from an earlier project, but I decided to give it a try because I found this open source “smart stepper” project. It uses pretty much the same encoder and they have developed hardware and firmware to turn a stepper into a closed loop servo. They also have a NEMA23 version. Very cool!
Apparently there are chinese knock-offs now too. I did read that there are big issues with noise on long step/dir wires, making the servo see step signals which were not there or it may temporarily see the wrong dir signal. So I don’t think they will work as-is for an MPCNC.
I was thinking about screwing a stop block of some kind to my spoil board, position the end mill against it, and then try to drive the steppers such that the end mill gets pushed against the stop block with more and more force. That would allow me to correlate the lag angle with the number of steps that I move the stepper. This number of steps will depend on the lengths of the belts, ie. the position in the workspace. So you’d need to do that at various locations to get a full picture.
An alternative is a linear encoder like this project. Should be quite easy to put one of those on a corner and attach the belt end to a roller/stepper.
I think that’s exactly right.
Thanks, me too! It’s a much deeper rabbit hole than I thought, but I’m enjoying it. I’m learning that there are all kinds of things that are affecting the rigidity. It’s lots of little things adding up, and it’s not always obvious.