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

And here's the machine in action (if it helps):
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

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.

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.

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

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.

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.

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.

Thanks so much for the suggestions!