[Bob La Londe]

I had a Chinese router a while back. Mostly its been retrofit with Gecko controls, and CNC Router Parts steppers, and a Smoothstepper. The 4th axis was also retrofit, but I always had a problem. On short moves it would seem to hunt for where to stop. I am not sure if the fact that it was at 12.5 steps per degree was part of the problem or not. It would also drift over time. It seemed to work beter on moves of over 20 degrees.

Anyway I am dragging it back out because I need it for a project, and I am changing a few things. For one I am increasing the ratio to 4.5:1. 10 tooth pulley on the stepper, and 45 tooth pulley on the chuck. Using a G540 that should give me 25 steps per degree. I know its probably not good enough for some types of work, but hopefully it will be good enough for the wood cutting I plan to do with it.

Is there anything I should do to improve consistent positioning? Reasonable RPM Limit? Reasonable acceleration limit? I really don't need speed. I need consistent positioning. Its going to be used more as an automatic indexer rather than as a continuous motion 4th axis.

How about always using it in ES mode? I add my 4th axis positioning manually in my machine operation headers so adding an extra two lines of code to put it into and take it out of ES mode is easy enough. This is currently running under Mach 3 (as LinuxCNC is not supported by an SS).

[Bob La Londe]

I have been proceeding with this improvement project, but I was hoping somebody would have some suggestions to help me reach my goal with it.

[awerby]

It's hard to say what was going on with your rotary table; having it "drift" would be concerning, if you were trying to make something with any accuracy at all. I doubt it has anything to do with Constant Velocity vs Exact Stop, though - it seems more likely that it's just loose, and liable to move under cutting forces. Certainly, if you're indexing, keeping to ES makes sense. And making all your moves in the same direction, locking it between moves, would rule out backlash and simple slop. Of course, if this is supposed to happen automatically, you'd need to figure out a way to unlock it between moves. Maybe a brake?

Andrew Werby
www.computersculpture.com

[Bob La Londe]

When it made a move it would finish rather oddly like it wasn't sure where to stop. Whatever was causing that I am sure was the primary problem.

[tahustvedt]

Was it a closed loop system or a regular stepper drive? If stepper then I'd suspect something was wrong with the stepper controller.