Machsupport Forum
G-Code, CAD, and CAM => G-Code, CAD, and CAM discussions => Topic started by: archerknives on November 19, 2017, 10:55:20 AM
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Hello
im new here (and with programming G code). We learned G code in school about 9 year ago now i have a small cnc mill and start experimenting.
Today i wanted to mill a round portion into a square piece of material. G code look like that:
G17 G90 F200;
G01 x-14 y-20;
G01 Z-16;
G01 Y0;
G02 X-14 Y0 I14 J0;
G01 x-13.5;
G02 X-13.5 Y0 I13.5 J0;
G01 x-13;
G02 X-13 Y0 I13 J0;
G01 x-12.5;
G02 X-12.5 Y0 I12.5 J0;
G01 x-12;
G02 X-12 Y0 I12 J0;
G01 x-11.5;
G02 X-11.5 Y0 I11.5 J0;
G01 x-11;
G02 X-11 Y0 I11 J0;
G01 x-10.5;
G02 X-10.5 Y0 I10.5 J0;
G01 x-10;
G02 X-10 Y0 I10 J0;
G01 x-9.5;
G02 X-9.5 Y0 I9.5 J0;
G01 x-9.1;
G02 X-9.1 Y0 I9.1 J0;
I tried this G code on several simulator and it looked good.
My Mach 3 somehow made an egg out of the circles.
https://ibb.co/iEG2A6
Sadly im not very experienced in Mach 3.
Could you guys please help me? Whats wrong? Settings, G code?
Thanks in advance
Daniel
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Hi Daniel,
In Config. / General Config. change the IJ Mode then regenerate the toolpath.
To avoid this problem all Gcode containing arcs should include the G90.1 or G91.1 as appropriate.
Tweakie.
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Hi Daniel,
You also need to check your Z axis dimensions and it's placing in the code.
It Is usual to have Z zero as the top surface of the work and your initial cut of X-16 is perhaps a bit steep.
Tweakie.
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Thanks for the reply. I look into the config and it was set to absolute. G code was also programmed in absolute if im not wrong..
When i changed to incremental the cirkles were round.
Sorry for my ignorance, but shouldnt it work with Absolute also?
Thanks in advance
Beste regards
Edit.
my zero is on top of workpiece center of cirkle.
i go to x-9 y-20 to clear workpiece and go down in z then go to the startpoint of the cirkle...
hope this makes sense
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ok i tried to programm it as "incremental"
in the simulator it seems fine..
https://www.pic-upload.de/view-34325582/Unbenannt.png.html
Mach 3 doesnt like it at all...
Tried to change the settings from IJ to avsolut and back to incremental... didnt fix my problem
Sorry if that might be a dumb question. in just learning
Any ideas?
Thanks in advance
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G code was also programmed in absolute if im not wrong..
Two different things.
There's Absolute G90 - Incremental G91.
But the problem is the IJ mode, which has it's own Absolute and Incremental modes, which are G90.1 (absolute IJ) and G91 (Incremental IJ).
The most common method, which most CAM programs use, is to program in Absolute (G90), with Incremental IJ (G91.1).
Be sure not to put both G90 and G91.1 on the same line in your g-code, or it may not work correctly.
G90 G91.1 (Don't do this.)
Proper method below:
G90
G91.1
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like i said noob at work :(
I didnt know that.
After putting both in different lines everything worked perfect!
Just finished maschining.
Thanks alot!!!
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ok now i maschined a part to try out the code and it worked.
But the part turned out to be not very round at all.
(https://preview.ibb.co/kLQY2m/IMG_20171119_200637.jpg) (https://ibb.co/cbj48R)
heres a video of the milling of a test piece.
https://youtu.be/wrK5LY8areU
Question is why.
I have backlash compensation on and measured it with a dail gauge. the backlash is compensated very well...
also tried to run slower because the motors might have trouble slowing down, speeding up. but didnt change.
Any idea? Is there a setting n Mach3 to eliminate this?
sorry for my dumb questions. total new here. try to learn...
Thanks in advance
Dan
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It could be flex in the material but I suspect backlash in the machine. Backlash comp. is OK but it is not the answer to all situations (toolpaths). Perhaps look toward reducing the actual backlash in the machine ?
Tweakie.
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im pretty sure it is not flex in that case. this material is very good /easy to maschine.
But i have quite a bit of backlash in the spindels (trapezoidal spindels) no ballscrews. as i also want to be able to mill manually ill keep the spindles.
I'll try to minimize the backlash by workung on the nuts tough...
thanks!
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Something else you should try is changing the toolpath to anti-clockwise as that will change the direction of loading on the lead-screws and may improve the backlash comp. performance. But overall nothing beats reducing the actual, mechanical, backlash.
Tweakie.
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tried that already.. same result.
looks like i have to disassamble and work on the nuts to eliminate/reduce backlash...
Thanks alot!
Dan