Squares and circles | Synthetos Forum

Started by Andrew on Feb 25, 2013 in TinyG Support. 5 replies, last activity Feb 26, 2013.

Andrew Feb 25, 2013 #

If I draw a square it comes out perfect, if I draw a circle it comes out with slightly flat sides. Diagonal lines also seem fine, which is confusing me, as I thought the flats on the circles were due to incorrect calibration on the X axis.

Please see this image

https://www.dropbox.com/s/i77qoi5df43ar8r/square_and_circle.jpg

X is horizontal and Y vertical.

The sides of the square a drawn perfectly, indicating that they are both set up correctly. The flat sides to the circle appear in all positions in the cutting area, and it's not the pen holder as the cutter does exactly the same (which I why I went back to the pen to check it out in the first place).

I've checked my GCode in ncplot and it looks fine. So now i'm stuck as to why my circles aren't circular! I should say that the problem is less obvious / not measurable in large circles.

Here is the circle G Code i'm running

G21 (Units: Metric)
G40 G90
F1
(Part: test_circle)
(Operation: No Offset, 0, T1: Mill/router, 2 mm diameter, 0 mm Deep)
M6 T1 (Mill/router, 2 mm diameter)
G43 H1
G00 Z2.5000
M03 S1000
X-4.6294 Y1.8891
Z0.5000
G01 Z0.0000 F100
X-4.2177 Y2.6854 F450
X-3.6704 Y3.3953
X-3.0052 Y3.9961
X-2.2433 Y4.4685
X-1.4094 Y4.7973
X-0.5302 Y4.9718
X0.3661 Y4.9866
X1.2506 Y4.8411
X2.0949 Y4.5400
X2.8719 Y4.0929
X3.5566 Y3.5144
X4.1269 Y2.8228
X4.5646 Y2.0406
X4.8557 Y1.1927
X4.9906 Y0.3066
X4.9651 Y-0.5895
X4.7801 Y-1.4666
X4.4414 Y-2.2965
X3.9600 Y-3.0526
X3.3513 Y-3.7107
X2.6348 Y-4.2494
X1.8337 Y-4.6516
X0.9737 Y-4.9043
X0.0824 Y-4.9993
X-0.8116 Y-4.9337
X-1.6795 Y-4.7095
X-2.4935 Y-4.3339
X-3.2272 Y-3.8190
X-3.8573 Y-3.1814
X-4.3634 Y-2.4415
X-4.7292 Y-1.6232
X-4.9430 Y-0.7527
X-4.9980 Y0.1420
X-4.8923 Y1.0322
X-4.6294 Y1.8891
G00 Z2.5000
M05
M05 M30

Can anyone help?

aldenStaff Feb 25, 2013 #

Looks like backlash in your mechanical setup. What kind of machine are you running?

Alden

Andrew Feb 25, 2013 #

ShapeOko, looking back at my first cuts though I didn't see these kind of flats on the sides of the circles. Are there any tests I can try to prove this. Would lowering the feed rate reduce the backlash?

Andrew Feb 25, 2013 #

I should add as well that i've heavily modified the X and Z axis to remove any flex.

I've repeated the tests as 200mm/min and 100mm/min the original was done at 450mm/min, to me the results look the same. If it was backlash would you expect to see the same results at different feed rates?

See this image https://www.dropbox.com/s/6vqqfwvn4yei2vx/feedrate_circles.jpg

Could there be something up with the stepper motor? I would expect there to be more problems, if it was a stepper motor issue.

By the way thanks for taking the time to answer my questions!

JuKu Feb 25, 2013 #

To me, looks like flex in the tip of your Sharpie.

Andrew Feb 26, 2013 #

OK so following your advice of backlash I set about tightening up the X axis belt, and guess what, you were right! The circles are much better, so it must be a mechanical issue. I confused myself, and thought I'd already gone through the mechanical tests.

Anyway thanks for your help.