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Author Topic: machine produces OVALS instead of CIRCLES???  (Read 2646 times)

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machine produces OVALS instead of CIRCLES???
« on: March 25, 2010, 09:14:32 PM »
Hello all,
I recently finished my homemade CNC 3-axis mill and have been experimenting with Mach 3 with some success. However, when I program a circle or an arc with simple G2 or G3 code, the result is not round but rather ovalish in shape. I did the axis calibration for a second time but the results were similar... Does it mean, I am not calibrating the axis properly, or is there anything else in the configurations that could cause that?
thanks in advance
M.

Offline Jeff_Birt

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Re: machine produces OVALS instead of CIRCLES???
« Reply #1 on: March 25, 2010, 09:30:02 PM »
It could be your configuration process, it could be backlash, it could also be your code. If you post your code it would be easy to rule that one out.
Happy machining , Jeff Birt
 

Offline RICH

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Re: machine produces OVALS instead of CIRCLES???
« Reply #2 on: March 25, 2010, 09:31:22 PM »
M.,
If the steps per unit are correct then it is probably a mechanical problem.

I don't know the extents of out of round you are experiencing. Here is a example for thought:
A rolled ball screw is used and it has a little more gain in one spot as compared to how the steps per units were
set based on say a long move....thus you get a little more inaccuracy from the ball screw, maybe a little backlash, maybe a little inaccuracy
in belts , table movement at spot, etc and summing al it up creates some ovality. So it is a matter do degree of accuracy of the whole machine.


RICH
Re: machine produces OVALS instead of CIRCLES???
« Reply #3 on: March 25, 2010, 09:52:54 PM »
Thank you guys.

The test program is:
%
G0 G17 G20 G40 G49 G80
G91 G28 Z0
T1M6
G0 G90 G54 X-0.5 YO S5500 M3
G43 H1 Z1.
Z.1
G1 X0 Z-.1 F10.
X0.5
G3 X0.5 I0.5 J0
G1 X0
X-0.5
G0 Z1.
G91 G28 Z0
M30
%


What is the best way to check for backlash?

Thanks
Max

Offline RICH

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Re: machine produces OVALS instead of CIRCLES???
« Reply #4 on: March 25, 2010, 10:25:26 PM »
Quote
What is the best way to check for backlash

Move the axis in one direction some amount, then put an indicator to measure the next move in the same direction ( say 0.500"), now move the axis
in the opposite direction. The indicator should show a travel of  0.500", if it reads 0.498" then the difference is a  backlash of 0.002".
The non-movement on change of direction is backlash and can be due to thrust bearing play or the ball nut.

Do the same for the other axis as well.

RICH
« Last Edit: March 25, 2010, 10:28:11 PM by RICH »