Need Help!- Flat spots on helical moves (G2/3)

[djdever]

Well I've got my mini-CNC moving around well in linear motions. However for some reason a helical coordinated motion creates 'flat spots'. (a 1" circle has 1/4" straight lines on 4 'sides')
It 'looks like' the accel/decel is too slow - but setting config values has no effect on output.
I was thinking:
1. Configuration / HAL settings
2. Backlash (seems little effect)
3. ??????????
Thanks in advance for the HELP!

[Zig]

Very carefully measure / estimate whether the flats are perpendicular to each other and whether they are parallel o the X Y axes of machine frame
?

[djdever]

Flat spots appear to be parallel to each other. Perpendicularity to the axis is difficult to judge - looks non-90º, but best I can measure says it is.
I've attached a scan of a circle with center mark for judgment.
Thanks for the help ... can you share your if ___ then ___ logic?

[Zig]

Well.. the flats do look like they are parallel to the oposite side.

And they sortof look parallel to the axes of motion but possibly not quite...

I would check backlash.. acceleration... and most probably the setup time settings in Your driver configuration. That is direction set up times.

This presumes that You are runing with stepper motors.

[vlmarshall]

I'm guessing that you went around that circle clockwise? If so, the flats are backlash. Look, for instance, at the 12 o'clock flat; as the table moves around to the peak Y position, the circle is fine. Then after passing 12o'clock, the Y stepper reverses and starts taking up the backlash in the leadscrew. It's not until the X has gone quite a way off of the centerline that the Y slop is gone and the table actually starts following the curve again, only to have the same thing happen in X at 9 o'clock, and so on.

[Zig]

Also check for any loose connections in couplings or soft and too compliant couplings between motors and leadscrews.

[djdever]

Perfect gentlemen (very good anyway)

I found a loose 'connection' in both axes. After 'tightening', reducing the backlash had a great effect on eliminating the flats.
I appreciate all the input!

(result attached)

[vlmarshall]

Excellent, I'm glad to hear you've gotten it worked out!