Maintaining constant velocity while switching on an output

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18 Oct 2019 18:37 #148213 by Arthur1
We are currently working on a project in which we apply are applying a patch of spray to a metal surface. This requires getting our CNC machine up to speed then turning on the spray (using the coolant flood command) at a precise position and then turning it off again at a precise position after it has traversed the desired patch. The problem we are having is that the machine slows down in between moves where we turn the spray on. This leads to the edges of the patch receiving a heavier treatment than the rest. I've made sure that G64 is turned on. We are running at relatively high speeds (300 ipm - 600 ipm). We are using a modified Shopbot system with a Mesa 5i25 -7i76 card setup. Is there any way we could do this while maintaining constant velocity? Or is there a way to signal the spray to turn on during the middle of a move? I feel like I'm missing something obvious.

A sample of the G-Code I'm using:

%
G17 G20
G80 G94
G64

G90
G1 Z 0.1 F50

G91
G1 F300

G1 X 3
M8
G1 X 3
M9
G1 X 3
G1 X -3
M8
G1 X -3
M9
G1 X -3
%

Thanks

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18 Oct 2019 18:52 #148214 by tommylight
linuxcnc.org/docs/html/gcode/m-code.html#mcode:m62-m65
Have a look at those, using flood or mist is not viable for that, as you've noticed.

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18 Oct 2019 19:20 - 18 Oct 2019 19:24 #148219 by Todd Zuercher
You will want m62,m63 since m64 and m65 will be queue busters just like m8 and m9.
Last edit: 18 Oct 2019 19:24 by Todd Zuercher.

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18 Oct 2019 19:49 #148222 by Arthur1
Thanks for the response. I tried setting up and using the M62 and M63 commands but still have the same issue. The motion slows down significantly between the linear moves.

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18 Oct 2019 19:51 #148223 by tommylight
Might have to increase acceleration quite a bit.

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19 Oct 2019 09:32 #148313 by Mike_Eitel
Look for G64. Probably you demand that stopping.

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21 Oct 2019 13:00 #148467 by Arthur1
I increased the acceleration significantly and it seems to have helped but there is still a very clear slow down stutter between moves.

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21 Oct 2019 14:25 - 21 Oct 2019 14:29 #148469 by Todd Zuercher
Are you sure you tried it with M62 and M63?
It doesn't seem to slow in my simulation, (It does slow with M64/M65 and M8/M9)
%
G17 G20
G80 G94
G64

G90
G1 Z 0.1 F50

G91
G1 F300

G1 X 3
M62p0
G1 X 3
M63p0
G1 X 3
G1 X -3
M62p0
G1 X -3
M63p0
G1 X -3
%
Last edit: 21 Oct 2019 14:29 by Todd Zuercher.

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21 Oct 2019 14:43 #148470 by Arthur1
I had been using both M62/M63 and M64/M65 for testing it out. It looks like another reset of the system seems to have helped fix that last little bit of slowdown. Don't know how and it doesn't make me confident that it will stay that way but I'll take it for now. Thank you all for your help.

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21 Oct 2019 15:11 #148474 by Todd Zuercher
There is one little thing you must remember about M62/M63. They require that a move be commanded after they are issued for their changes to take effect.

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