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### Author Topic: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...  (Read 809 times)

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#### MojsterMiha

• 65
##### Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« on: November 08, 2020, 06:26:30 AM »
I have read a lot of posts about circle cutting - no circle but oval, and checked and tried many suggestions but no success.

My machine still doesn’t cut correct circle.

1.  X and Y backlash les than 0,03mm
2.  Steps per unit equal to both axis - the same ratio between AC servo motor and ball screw
3. Following error on both axis during circle cutting near 0 - there are 750W AC servos on light machine - over dimensioned motors.
4. Acceleration/deceleration equal to both axis.
5. When cutting square 100 x 100 mm, both dimensions are in +/- 0,02mm
6. Circle dimension in X and Y axis is also 100mm +/-0,02mm (when cutting circle 100mm)
7. The difference in diameter measured in 45° and - 45° is 0,6mm
8. By cutting circle in CCW or CW direction, diameter difference in 45°and -45° remain the same but vice-versa.
9 Cutting speed doesn’t change result - cutting 150mm/min or 1500 mm/min. gives the same result.
10. I'm using LPT BB

I have no idea what else I can do to solve this issue.
Any suggestion appreciated…

« Last Edit: November 08, 2020, 06:31:21 AM by MojsterMiha »

#### Tweakie.CNC

• 9,042
• Super Kitty
##### Re: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« Reply #1 on: November 08, 2020, 08:21:44 AM »
PEACE

#### MojsterMiha

• 65
##### Re: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« Reply #2 on: November 08, 2020, 10:41:52 AM »
It's a simple code with IJ:

M3 S12000
G17
G0 X53 Y0
Z2
G1 Z-2 F800
G3 X-53 I-53 J0
G3 X53 I53 J0
G00 Z20
M5
M30

Also with R I have same issue:

M3 S12000
G17
G0 X24 Y0
Z2
G1 Z-4 F1000
G2 X-24 R24
G2 X24 R24
G00 Z20
M5
M30

Cutter is D6

Thanks

#### Graham Waterworth

• 2,579
• Yorkshire Dales, England
##### Re: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« Reply #3 on: November 08, 2020, 11:19:37 AM »
There is nothing wrong with the code, maybe it should have a G90 in it but it will still work without.

My guess is something is loose or slipping on a shaft if your steps are set to the correct values.
Without engineers the world stops

#### MojsterMiha

• 65
##### Re: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« Reply #4 on: November 08, 2020, 01:01:36 PM »
Yeah, that would probably be most likely, but I checked everything and there’s nothing like that.
The beginning and end of the circle are also completely equal - there is no visible transition at all.
I also tried repeating the code:
0.1
-0.1
0.1
.
.
.
on both axes and when measured with a measuring indicator, it shows a movement of 0.17 mm on both axes (only 0.03 mm difference)

Even after prolonged milling, the machine remains in the same position. If I repeat the program, it goes exactly the same path - so even after one hour of milling, nothing slips.
Even if I push the X or Y axis with my hands in one  or another direction while milling the circle , the shape of the circle itself does not change.

Tomorrow I will try to cut a circle programmed from short lines (g1 only). I will report what the result will be ...

#### Graham Waterworth

• 2,579
• Yorkshire Dales, England
##### Re: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« Reply #5 on: November 08, 2020, 05:15:08 PM »
It may be a good idea to run the same circle with a feed of 100mm/min and see if that makes it round.  This may be a CV issue.
Without engineers the world stops

#### joeaverage

• 7,562
##### Re: Circle not circle but oval - no backlash on the axis, steps per unit set OK,...
« Reply #6 on: November 12, 2020, 04:46:31 AM »
Hi,
have you measured how square the X and Y axes are to each other?. Only a very small angular deviation from
900 will have a significant effect on a circular interpolation path.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'