Need help with servo tuning



I was looking at your website and noticed you had built a Industrial Hobbies Mill, using the Kelinginc KL34-170-72 850oz. Servo motors. I just got done building one as well. I am having some issues with the machine tolerances. I was wondering if you would be able to help me make sure my motors are tuned properly. I have tried going thru your post and spreadsheet but alot of that was greek to me. This is my first time building with Servos. I have built a couple of stepper cnc mills in the past, several years ago. Most of what i learned from them has been forgotten due to not keeping up with projects like that. I will outline my mill setup below and if you would help me come to the correct motor velocity and acceleration setting? All of the hardware were purchased from Charter Oaks Automation. It was stuff left over from there old machine layout.

All ballscrews are 20mm with 5mm pitch.

Motors are Kelinginc KL34-170-72 850 oz. DC Servo motors

X/Y Gear reduction is 2:1, with 50 tooth pulley on ballscrew and 25 tooth pulley on motor.

Z Gear reduction is 3:1, with 72 tooth pulley on ballscrew and 25 tooth pulley on motor.

my current motor tuning is as follows: X/Y/Z  velocity: 150, and Acceleration: 30

Some of the issues i’m having is, when i cut an outside contour it is coming out .005-.010 larger than any other feature. All other features are coming out to measurement.

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Rod, if you’re hoping to somehow use the values I used to tune my mill, it won’t work for a number of reasons.  The main one is that every mill, servo motor, and driver are different.  They needed to be tuned together as a unit.  You’re going to need to either master servo tuning using the techniques I describe, or you’ll need to acquire some servo drives that auto-tune or make the tuning much simpler.

I no longer own the Industrial Hobbies mill, but it was my plan to move off the Gecko servo drives and onto some nicer drives for this reason.  Servo tuning the Gecko’s was messy and I was confident a self-tuning drive could get better results.

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