Beraht
06-26-2021, 02:09 AM
Could someone explain the "what and where" of signal processing for a ShopBot? Start with the gcode toolpath file being processed in the computer software to the processing that takes place in the control card, control board and the drivers that ends up being a step for a motor?
As a side note, this question is driven by weird behavior being seen on my 5x10 Alpha. The behavior is best observed when cutting a straight line at constant Y value. I have a simple demo code that should cut a straight line from X7,Y17 to X19,Y17. The cut is 0.25" deep. There are ten 0.15" high x 0.5" long 3D tabs. The gcode for this has zero change in the Y value, but when the cut is made, every Z movement is accompanied by a ~1/8" negative Y move. Going up and down a 3D tab is two Z moves and the cut location shifts ~1/4" to the negative Y direction at each tab.
This only happens on a toolpath with an X move. A similar line oriented 90 degrees so that only Y & Z are moving will cut perfectly.
Now I know some of you are saying that can't be, but here is the code that results in a 12" travel in the X direction and an ~2.5" travel in the negative Y direction:
M3,7.000000,17.000000,-0.250000
M3,7.280000,17.000000,-0.250000
M3,7.600000,17.000000,-0.100000
M3,7.920000,17.000000,-0.250000
M3,8.480000,17.000000,-0.250000
M3,8.800000,17.000000,-0.100000
M3,9.120000,17.000000,-0.250000
M3,9.680000,17.000000,-0.250000
M3,10.000000,17.000000,-0.100000
M3,10.320000,17.000000,-0.250000
M3,10.880000,17.000000,-0.250000
M3,11.200000,17.000000,-0.100000
M3,11.520000,17.000000,-0.250000
M3,12.080000,17.000000,-0.250000
M3,12.400000,17.000000,-0.100000
M3,12.720000,17.000000,-0.250000
M3,13.280000,17.000000,-0.250000
M3,13.600000,17.000000,-0.100000
M3,13.920000,17.000000,-0.250000
M3,14.480000,17.000000,-0.250000
M3,14.800000,17.000000,-0.100000
M3,15.120000,17.000000,-0.250000
M3,15.680000,17.000000,-0.250000
M3,16.000000,17.000000,-0.100000
M3,16.320000,17.000000,-0.250000
M3,16.879999,17.000000,-0.250000
M3,17.200001,17.000000,-0.100000
M3,17.520000,17.000000,-0.250000
M3,18.080000,17.000000,-0.250000
M3,18.400000,17.000000,-0.100000
M3,18.719999,17.000000,-0.250000
M3,19.000000,17.000000,-0.250000
And no, I am not making this up. I have run a number of tests swapping drives, cables, etc. as suggested by ShopBot Support. Current plan being suggested: try a new control card first and if that doesn't fix it, try a new control board. Would be great to learn someone else has seen such a thing and found the fix!
As a side note, this question is driven by weird behavior being seen on my 5x10 Alpha. The behavior is best observed when cutting a straight line at constant Y value. I have a simple demo code that should cut a straight line from X7,Y17 to X19,Y17. The cut is 0.25" deep. There are ten 0.15" high x 0.5" long 3D tabs. The gcode for this has zero change in the Y value, but when the cut is made, every Z movement is accompanied by a ~1/8" negative Y move. Going up and down a 3D tab is two Z moves and the cut location shifts ~1/4" to the negative Y direction at each tab.
This only happens on a toolpath with an X move. A similar line oriented 90 degrees so that only Y & Z are moving will cut perfectly.
Now I know some of you are saying that can't be, but here is the code that results in a 12" travel in the X direction and an ~2.5" travel in the negative Y direction:
M3,7.000000,17.000000,-0.250000
M3,7.280000,17.000000,-0.250000
M3,7.600000,17.000000,-0.100000
M3,7.920000,17.000000,-0.250000
M3,8.480000,17.000000,-0.250000
M3,8.800000,17.000000,-0.100000
M3,9.120000,17.000000,-0.250000
M3,9.680000,17.000000,-0.250000
M3,10.000000,17.000000,-0.100000
M3,10.320000,17.000000,-0.250000
M3,10.880000,17.000000,-0.250000
M3,11.200000,17.000000,-0.100000
M3,11.520000,17.000000,-0.250000
M3,12.080000,17.000000,-0.250000
M3,12.400000,17.000000,-0.100000
M3,12.720000,17.000000,-0.250000
M3,13.280000,17.000000,-0.250000
M3,13.600000,17.000000,-0.100000
M3,13.920000,17.000000,-0.250000
M3,14.480000,17.000000,-0.250000
M3,14.800000,17.000000,-0.100000
M3,15.120000,17.000000,-0.250000
M3,15.680000,17.000000,-0.250000
M3,16.000000,17.000000,-0.100000
M3,16.320000,17.000000,-0.250000
M3,16.879999,17.000000,-0.250000
M3,17.200001,17.000000,-0.100000
M3,17.520000,17.000000,-0.250000
M3,18.080000,17.000000,-0.250000
M3,18.400000,17.000000,-0.100000
M3,18.719999,17.000000,-0.250000
M3,19.000000,17.000000,-0.250000
And no, I am not making this up. I have run a number of tests swapping drives, cables, etc. as suggested by ShopBot Support. Current plan being suggested: try a new control card first and if that doesn't fix it, try a new control board. Would be great to learn someone else has seen such a thing and found the fix!