depth of cut is not correct

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KRG
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depth of cut is not correct

Post by KRG » Fri Dec 18, 2015 6:46 pm

I set my TARGET DEPTH to -.10 and STEP DOWN rate at .05 Shapeoko 3 makes 2 passes. The total cut depth is .1875 What am I doing wrong???? The first cut is very deep (about .15) and the second cut is very shallow (about .05) Also - what is ROUGHING CLEARANCE ???

WillAdams
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Re: depth of cut is not correct

Post by WillAdams » Fri Dec 18, 2015 6:59 pm

KRG wrote:I set my TARGET DEPTH to -.10 and STEP DOWN rate at .05 Shapeoko 3 makes 2 passes. The total cut depth is .1875 What am I doing wrong???? The first cut is very deep (about .15) and the second cut is very shallow (about .05)
You may not be getting the machine properly zeroed on the top surface of the stock, or the machine may be getting pulled into the cut, or you may be losing steps. Please see: http://www.shapeoko.com/wiki/index.php/ ... quare_Test and the balance of the wiki.
KRG wrote:Also - what is ROUGHING CLEARANCE ???
http://www.shapeoko.com/wiki/index.php/Glossary#R
Roughing Clearance (MakerCAM) How much material will be left when roughing out material for the current operation as a roughing pass, and instead, will only be removed w/ a second operation, the finishing pass which may have different settings for stepover, feed rate, &c. so as to leave a nicer finish.
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KRG
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Re: depth of cut is not correct

Post by KRG » Sat Dec 19, 2015 4:05 pm

I have really tried to read all the info posted on the wiki page. I am satisfied with the X and Y orientation and travel. I am satisfied to the angle orientation of the Z axis. But I can find nothing concerning adjust the depth of the z axis especially in relation to Makercam program. Last night I ran my same SVG that I had problems with but I raised the bit from the surface 2.0 mm and used that as the ZERO mark. The depth of cut was much more satisfactory. But that still does not correct the problem or my understanding of what I am doing wrong. I input into the machine TAGET DEPTH of -.10 with a STEP DOWN of .05. Should the machine not make 2 passes each being .05 ??? The first cut is .15. WHY when I told it .05 ??

Atonwa
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Re: depth of cut is not correct

Post by Atonwa » Sun Dec 20, 2015 1:39 am

You might want to check your Gcode manually. I had this exact problem with a diamond drag bit I was trying to use today. Input a Z value of .125 deep and it goes .375. Could not figure out why. Looked in Gcode and the first Z raise was .8". Because of my spoilboard and the length of the drag the Z could not raise the .8" it wanted. It moved as far as it could which was about .5" and then plunged down the .8" which overshot my Z. It took a while to figure out exactly what was happening but check your first move prior to cut in your gcode and shorten it if necessary to see if that helps.
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WillAdams
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Re: depth of cut is not correct

Post by WillAdams » Sun Dec 20, 2015 9:31 am

Agree.

Break things down into steps.

Figure out what Z movement should happen for a given step and a way to measure it.

Perform each step and measure Z before and after w/o load — if everything works, repeat as confirmation w/ a cutting load. If it then fails, you’re missing/ losing steps.
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KRG
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Re: depth of cut is not correct

Post by KRG » Sun Dec 20, 2015 12:50 pm

I don't understand the term "missing/losing steps." How is that corrected?

WillAdams
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Re: depth of cut is not correct

Post by WillAdams » Sun Dec 20, 2015 11:52 pm

Missing / losing steps is when the micro controller sends a signal to move the stepper motors, but the matching movement is not made. Possible reasons:

- overheating stepper driver --- fix by adding active cooling
- slipping belt pulley --- fix by tightening set screw and0/or filing a flat on the shaft
- belt skips a tooth --- fix by increasing belt tension
- insufficient motor torque to make the requested movement --- adjust settings in Grbl / reduce feed rate

Probably others.
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KRG
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Re: depth of cut is not correct

Post by KRG » Wed Dec 23, 2015 7:32 pm

Will- Would the suggestions you gave such as skipping a tooth, insufficient motor torque, etc. result is a shallow cut? My problem is the cut is too deep. Here is the first few lines of code:


G20 G90 G40

(follow path 1)
G0 Z0.5
T0 M6
G17
M3
G0 X3.7871 Y0.3932
G1 Z-0.05 F10
G2 X3.7496 Y0.4008 I0.0493 J0.3361 F30
G2 X3.718 Y0.4114 I0.066 J0.2501
G2 X3.6884 Y0.4263 I0.0804 J0.1972
G2 X3.6674 Y0.442 I0.0687 J0.1138
G2 X3.636 Y0.4764 I0.1721 J0.1882
G2 X3.6202 Y0.5044 I0.0977 J0.0739
G2 X3.6108 Y0.5357 I0.1637 J0.0661
G2 X3.5983 Y0.6131 I0.9987 J0.2009
G3 X3.594 Y0.6391 I-0.301 J-0.0368
G3 X3.5864 Y0.6694 I-0.4162 J-0.0881
G3 X3.5766 Y0.6991 I-0.4345 J-0.1259
G3 X3.5653 Y0.7269 I-0.3905 J-0.1431
G2 X3.5499 Y0.7646 I0.5346 J0.2408
G2 X3.5438 Y0.7851 I0.15 J0.0554
G2 X3.5407 Y0.8061 I0.1476 J0.033
G2 X3.5392 Y0.8436 I0.4679 J0.0372
G2 X3.5437 Y0.9015 I0.38 J-0.0002

Am I not correct that it is sending instructions for the Z axis cut to be -.05? And yet the cut is .15??? This is very confusing to me.

cvoinescu
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Re: depth of cut is not correct

Post by cvoinescu » Thu Dec 24, 2015 4:53 pm

KRG wrote:Will- Would the suggestions you gave such as skipping a tooth, insufficient motor torque, etc. result is a shallow cut? My problem is the cut is too deep.
Sure, if the machine misses steps as it lifts the Z axis. It's much more likely for it to fail to lift the heavy carriage than to fail to lower it, so you end up deeper than expected.

Does that G0 Z0.5 lift it to 0.5 inches above the stock? Is the zero actually on the surface of the stock?
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KRG
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Re: depth of cut is not correct

Post by KRG » Fri Dec 25, 2015 3:36 am

OK- that makes sense. Is it does lift .5 above the stock and zero is right on the surface.

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