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Author Topic: Finish Z Move before X or Y  (Read 704 times)

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Finish Z Move before X or Y
« on: March 02, 2018, 01:37:11 PM »
I am having an issue with my code. When I program a move on the Z to move the cutter into the work, before it reaches it's bottom position, the X or Y move begins.

Attached is the code

%
O0100
(PROGRAM NAME - PARTITION2NO SLANT.NC)
(DATE - FRI. 03/02/2018 ,TIME - 11:18AM)
(POST -  Mach3 )
(TOOL LIST)

G00 G90 G17 G54 G40 G49 G80
T1 M06 (1/4 FLAT ENDMILL - STANDARD)
G90 S14000 M03
G00 G54 X66.036 Y203.2
(G43 H1 Z25.4)

Z2.54
G01 Z-20. F2031.24 (here is where it happens)
Y100.806 F3562.48 (this move begins before the Z is in position. I have even tried to program a P5.0, but no effect)
G01 Y203.2
G00 Z5.08
X187.194
G01 Z-20. F2031.24
Y100.806 F3562.48
G01 Y203.2
G00 Z5.08
X308.352
G01 Z-20. F2031.24
Y100.806 F3562.48
G01 Y203.2
G00 Z5.08
X429.51
G01 Z-20. F2031.24
Y100.806 F3562.48
G01 Y203.2
G00 Z5.08
X550.668
G01 Z-20. F2031.24
Y100.806 F3562.48
G01 Y203.2
G00 Z5.08
X671.826
G01 Z-20. F2031.24
Y100.806 F3562.48
G01 Y203.2
G00 Z5.08
Z25.4
M05
G00 X0 Y1000
T1 M06
M30
%

Any help Please.

Thanks.
Re: Finish Z Move before X or Y
« Reply #1 on: March 02, 2018, 02:26:02 PM »
If I'm not mistaking, it is because you are in CV mode and your Z move is a G01 Feed move, mach is smoothing the transition from 1 line to the next.

Page 27 from the Mill GCode Programming Manual explains Exact Stop vs Constant Velocity.
« Last Edit: March 02, 2018, 02:29:08 PM by Cbyrdtopper »
Chad Byrd
Re: Finish Z Move before X or Y
« Reply #2 on: March 02, 2018, 02:36:10 PM »
I'm assuming this is plunging into material and then cutting.  Adding G04 P50 on each Z Plunge move will fix your issue.  

If you are using a post processor, this could be annoying to change each instance.  But it will fix your issue.

G01 Z-20. F2031.24 (here is where it happens)
G04 P 50 (Add this line here)
Y100.806 F3562.48 (this move begins before the Z is in position. I have even tried to program a P5.0, but no effect)
Chad Byrd

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Re: Finish Z Move before X or Y
« Reply #3 on: March 02, 2018, 02:54:57 PM »
This is exactly what is happening.  Constant Velocity (CV) is a misnomer.  It really should be called Velocity Blending.  And CV is highly dependent on the motor tuning.  A lower accel/decel value will cause more "rounding" in the blended moves.  Higher values stay closer to the actual path.  Obviously, you want to set your accel/decel values as high as your hardware will allow to get the best results.  For servo systems, I usually tick the accel value to the point where the drive faults out and then back it down 10% for a little bit of margin.  For steppers, that point is where you start losing steps.  If you play around with it, you may get your system to the point where it really won't make much difference.

I also find it useful to use CV during roughing and constant stop on the last finish pass.  Tailoring the tool path in the CAM system can accomplish this.  If your machine is acceleration challenged, then you might have to modify the post processor to include G09 (one shot exact stop) for the lone Z feed move.  I like that better than using a G04 dwell.  But to each their own. 

e.g.

G09 G01 Z-20. F2031.24 (here is where it happens)

Steve
Re: Finish Z Move before X or Y
« Reply #4 on: March 02, 2018, 03:07:52 PM »
Thanks for the input.  It works as intended now.
Re: Finish Z Move before X or Y
« Reply #5 on: March 02, 2018, 03:36:47 PM »
Thanks for the input Steve.  I thought there was a One Shot Exact Stop, I couldn't remember what the code was.  Thanks for bringing that to Light as well, that would be my preferred method as well.
Chad Byrd