Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: highplainsjames on September 10, 2023, 08:35:27 PM

Title: CNC Calibration: Circles Not Round
Post by: highplainsjames on September 10, 2023, 08:35:27 PM

I'm a long time programmer but, completely new to cnc machining.  I have a homebrew 3 axis cnc router, but I'm unable to get round circles.  Here's what I'm seeing instead:

https://drive.google.com/file/d/1ZQ8s6cXgfiWKXvV0jc2hIqa1n8RjUfTP/view?usp=sharing (https://drive.google.com/file/d/1ZQ8s6cXgfiWKXvV0jc2hIqa1n8RjUfTP/view?usp=sharing)

And here's the machine in action (if it helps):
https://drive.google.com/file/d/17-PwM5NcpHRFrbq4lnLBYUZ_5qPY7ml2/view?usp=sharing (https://drive.google.com/file/d/17-PwM5NcpHRFrbq4lnLBYUZ_5qPY7ml2/view?usp=sharing)

Also, here's where I'm attempting to measure backlash:
https://drive.google.com/file/d/1_K-X9IH7ygsE3pvGv4LZB0IbhyUbAZRY/view?usp=sharing (https://drive.google.com/file/d/1_K-X9IH7ygsE3pvGv4LZB0IbhyUbAZRY/view?usp=sharing)

Here's what I've tried so far:
* Calibration and adjusting motor setup
* Slowing the max machine speed down
* Measuring for backlash

I'm happy to try additional things but, given my inexperience I'm not sure what to try next.

Any suggestions would be greatly appreciated.

Title: Re: CNC Calibration: Circles Not Round
Post by: Tweakie.CNC on September 11, 2023, 12:48:21 AM

Just as a test...

Half your Velocity and Acceleration settings in Motor Tuning for each of your X and Y axis, saving the changes.

Do your circles now come out round ?

Tweakie.

Title: Re: CNC Calibration: Circles Not Round
Post by: TPS on September 11, 2023, 02:05:38 AM

also make sure in Config -> General Config - Motion Mode -Exact Stop is selected

to measure backslash:

-jog axis tooward gauge
-zero gauge
-zero axis DRO
-now switch to handwheel mode single step and a small jog step (0,1 or 0,01)
-now jog axis away from gauge in single step's and watch gauge
-when gauge starts to move read your axis DRO to see your backslash

Title: Re: CNC Calibration: Circles Not Round
Post by: highplainsjames on September 11, 2023, 07:36:33 AM

Thanks so much for the suggestions!  It's really nice to be able to get advice from experts.

Unfortunately, I am traveling to NYC for work this week but I will give both a shot next weekend and report the results.

Title: Re: CNC Calibration: Circles Not Round
Post by: highplainsjames on September 18, 2023, 09:22:41 AM

I didn't get much time to work with the machine this weekend, but I did try the first suggestion.  I halved both the velocity and acceleration settings for both the X and Y axis.

Here's the result:
https://drive.google.com/file/d/1_pP5vEa1fsFVHLk5qdAgGGdQbXpwl_3N/view?usp=sharing

Maybe slightly more round, but overall still not super precise.

Title: Re: CNC Calibration: Circles Not Round
Post by: Tweakie.CNC on September 18, 2023, 10:08:26 AM

Thats a terrible result & no good at all  :(

If your up for it, another test...

Tape a felt tip pen to your Spindle or Z axis. Will it now draw a round circle on a piece of paper or card ?
If it does then there is a mechanical issue with your machine, if it is still a bad circle then it could be related to your GCode or possibly a bad Mach setting somewhere.

Perhaps .zip and post a copy of your GCode so we can test it and also a copy of <your profile> .xml file (typically Mach3Mill.xml) from your Mach3 folder. The .xml file contains all your machine settings and we can test that they are correct or otherwise.

Tweakie.

Title: Re: CNC Calibration: Circles Not Round
Post by: aslaleratu on October 17, 2023, 08:02:35 AM

Thanks so much for the suggestions!