I discovered this was a problem while making my tapping arms. Due to the high rate of feed (50 IPM) and some abrupt changes of direction to follow the profile, I hadn’t really encountered the problem before. I had heard on one individual having an issue with wildly different motor tuning on a knee versus his X and Y axis. It had been said this was a bug in Mach.

In any event, as I discovered early in my machining of the axis arms, it isn’t a good idea to have different accelerations on two axes. I wouldn’t have noticed it had it not been for easing back the accel on the X axis because it was faulting too much when I run with two 6″ vises on the table. I lowered the X axis accel to match the Z and forgot about it. This latest job making a tapping arm reminded me in short order that something needed tending to.

It seems odd to me that Mach3 doesn’t account for this, and it ought to be classified as a bug. Mach’s trajectory planner should be able to properly choreograph a coordinated move across n-axes with a different acceleration and top velocity on each. If nothing else, the lazy algorithm would simply limit all the coordinated axes to the least acceleration and velocity of any axis involved at the time.

In any event, if you think you’re doing yourself a favor by finding each axis’s maximum performance envelope, you might in fact be doing the opposite until Mach learns to deal with it better.

BTW, the symptom will be that the tool follows the coordinated move’s path in a very sloppy way. Going around the pivot point on the tapping arm swing block it was painfully obvious to the naked eye something was wrong–no calipers or micrometers needed.

 

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