Mach 3 settings for 4th rotary axis

[chazw44]

I added a 4th rotary axis to my homemade cnc machine which has been running flawlessly for over a year and seem to have an issue with the stepper motor positioning. I am trying to test it and am trying to turn a 2" square blank into a cylinder. The motor rotates the blank, but instead of turning it a few degrees and making a pass with the router, it turns the motor about 30 times and takes a pass then turns another 20 0r so revolutions and then another pass. I have all the motors set the same in Mach 3 Motor Tuning and the a axis is set to angular. I've been playing with the settings, but am getting nowhere fast. Am I missing something very obvious with the configuration? Has anyone run into this problem and have a solution? Thanks for any help

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[awerby]

I don't think you can use the same steps per unit setting for a rotary axis as for a linear one. Remember, your units will be mm or inches for a linear axis, but they're degrees for a rotary one. So you have to figure out a setting that will give you the right number of steps to turn the motor one degree.

[chazw44]

Thanks for responding Andrew. I initially was thinking along those lines but I thought the mach 3 software automatically figured that out. It seems that as the A axis rotates and the display increases from say 0 to 30 the distance is advancing 30 inches linearly. I read about a diagnostic on another post that helps set the distance that the motor actually advances with the actual distance you are shooting for. I guess I'll have to investigate that route.

[ger21]

What is the gear ratio on your 4th axis? It's simple math to calculate the number of steps per degree.

[chazw44]

Gerry... My stepper motor on the 4th axis is a direct drive ...no gear ratio. I think I got the problem resolved. Just got done running a test and appears to turn a full 360 degrees when told to. I divided the steps per revolution by 360 and got the steps per degree. Then tweeked the a axis setting in Mach 3. I think I'm good to go.

Thanks
Charlie