Hello Guest it is December 15, 2019, 07:37:56 AM

Author Topic: G03 arcs are smooth, G02 arcs are jerky. Help!  (Read 1009 times)

0 Members and 1 Guest are viewing this topic.

G03 arcs are smooth, G02 arcs are jerky. Help!
« on: December 22, 2016, 03:16:56 PM »
I was running an older CAM program that was outputting arcs as lines.  That worked fine for me.  I just upgraded to RhinoCAM 2017 and thought I'd look into IJK instead of arcs-as-lines while I was regenerating some files.

My test file is a simple 8" x 8" rectangle, but I've put a 1" radius on all four corners so I have some arcs.  I'll post some gcode below.

PROBLEM: after every G01 line segment there is a pause just before the following G02 arc.

WEIRDNESS: if I reverse the direction of cut so the output contains G03 arcs (CCW) there is no pause after G01 lines.

I have a G64 turning on CV mode. 

I have "stop CV on angles >" set to 89.  If I turn this option off completely so I'm always running CV, there are no pauses for G02 arcs.  I need to leave it turned on though because I regularly cut inside corners that I need to be square.

This all leads me to believe it's a CV related quirk I'm not understanding.

Has anyone seen this weirdness before?

G00 G49 G40.1 G17 G80 G50 G64 G90
G20
(** CW G02 ARCS - pausing before all arcs **)
(**)
M6 T1
M03 S12000
G00 Z0.2500
X-0.7500 Y-0.2500
G01 Z-0.1000  F120.0
X-0.5000
G17
G03X-0.2500Y0.0000I-0.5000J0.0000
G01 Y3.0000
G02X1.0000Y4.2500I1.0000J3.0000
G01 X7.0000
G02X8.2500Y3.0000I7.0000J3.0000
G01 Y-3.0000
G02X7.0000Y-4.2500I7.0000J-3.0000
G01 X1.0000
G02X-0.2500Y-3.0000I1.0000J-3.0000
G01 Y0.0000
G03X-0.5000Y0.2500I-0.5000J-0.0000
G01 X-0.7500
G00 Z0.2500
M5 M9
M30



G00 G49 G40.1 G17 G80 G50 G64 G90
G20
(** CCW G03 ARCS - works perfectly **)
(**)
M6 T1
M03 S12000
G00 Z0.2500
X-0.7500 Y0.2500
G01 Z-0.1000  F120.0
X-0.5000
G17
G02X-0.2500Y0.0000I-0.5000J-0.0000
G01 Y-3.0000
G03X1.0000Y-4.2500I1.0000J-3.0000
G01 X7.0000
G03X8.2500Y-3.0000I7.0000J-3.0000
G01 Y3.0000
G03X7.0000Y4.2500I7.0000J3.0000
G01 X1.0000
G03X-0.2500Y3.0000I1.0000J3.0000
G01 Y0.0000
G02X-0.5000Y-0.2500I-0.5000J0.0000
G01 X-0.7500
G00 Z0.2500
M5 M9
M30
Re: G03 arcs are smooth, G02 arcs are jerky. Help!
« Reply #1 on: December 24, 2016, 05:17:21 PM »
Hi mikep,
I can't really think of anything that would explain it, the code looks OK.

May I suggest some experiments that might isolate the problem.

With a blank in the machine why don't you try MDIing some arcs to see if the fault occurs. It would establish whether its
faulty code or whether something peculiar is happening with the machine.

It occurs to me that if the arcs are OK in one direction but falter in the other then one axis is struggling to step in the reverse direction.
I note that you've posted before on this subject and have stated that linear moves in either direction are fine which would tend to make you
think that my thought is wrong. I don't know whether your BOB has LEDs on the outputs but mine does. I've noticed that if you call a move,
say the X axis, to the right, the DIR pin, on my machine at least is low, and it stays that way until the end of the move, and in fact will stay
that way indefinitely after the move until Mach changes it to  high when called on to move left. That is to say that the DIR pin is persistent.

During arc moves it may not be. What I'm thinking is that the DIR pin is changing but is not established long enuf before the STEP pulse arrives.
I use Vexta drivers and they have superb documentation and there is a specification for how long the DIR input must be established before the
STEP input goes high and steps the motor, its not long, about 0.5us from memory. Maybe one of your drivers is a bit slow.

Try some MDI acrs to gets the fault to recur. Then on the motor tuning page try upping the direction pulse a bit maybe a few us and see
whether it cures the fault.

Craig
My wife left with my best friend...
     and I miss him!
Re: G03 arcs are smooth, G02 arcs are jerky. Help!
« Reply #2 on: December 31, 2016, 11:14:06 AM »
Thanks for the reply Craig.  I'm pretty sure it's not the machine, but I'm willing to explore anything to rule things out.

As I say , if I turn off the "stop CV on angles >"  option, it runs flawlessly in either direction.  That leads me to believe I need to work on some CV setting(s) to solve the problem.

Mike