Machsupport Forum

Mach Discussion => FAQs => Topic started by: Uzito on April 21, 2022, 08:57:29 AM

Title: How do I mill a Perfect Circle?
Post by: Uzito on April 21, 2022, 08:57:29 AM

Hello all.
I have a newly built CNC machine. I am happy that it is functional.

I have done Automatic Calibration on all 3 axis and they are perfect.
Currently, I am doing test runs to see that it mills with acceptable accuracy.
Whenever I mill a Circle, the end result is an elongated 'circle'. See attached image. (Each of the 'circles' in the image, is the result of a different mill test.)

I have tried playing around with the Velocity and Acceleration settings in Mach 3 but the situation is not improving.
What might be the problem?  Please help.

Title: Re: How do I mill a Perfect Circle?
Post by: JohnHaine on April 21, 2022, 10:49:56 AM

Clearly not actually properly calibrated and possibly losing steps. Do the settings as a result of the autocalibration correspond to calculations?

Title: Re: How do I mill a Perfect Circle?
Post by: Uzito on April 21, 2022, 11:09:43 AM

Quote from: JohnHaine on April 21, 2022, 10:49:56 AM

Clearly not actually properly calibrated and possibly losing steps. Do the settings as a result of the autocalibration correspond to calculations?

I have not done calculations to counter check the AutoCalibration results. I will need to do the maths and see. Thanks John.

Anyone else with a different view and/or solution?

Title: Re: How do I mill a Perfect Circle?
Post by: JohnHaine on April 21, 2022, 12:35:45 PM

It's very straightforward if you know the screw pitch, stepper-to-screw gearing, steps per rev (usually 200) and microstep ratio.  See the Mach manual.

Also try some back-and-forth moves from 0 to 100mm back to 0 say and make sure it always returns exactly to zero to check for lost steps.  Do you have a dial indicator for assessing exact stop position?

Title: Re: How do I mill a Perfect Circle?
Post by: JohnHaine on April 21, 2022, 01:50:54 PM

Oh, and you may have backlash...