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Author Topic: Not Beef Jerky.. Just Jerky...  (Read 5326 times)

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Offline Chris.Botha

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Not Beef Jerky.. Just Jerky...
« on: August 24, 2009, 05:32:21 AM »
Hello all...

I have picked up a problem which is neither a mill bug nor a Mach bug but an "Understanding Bug"..

i notice that at about 700mm/min and up I get severe vibration running through my setup, to the extent that i can visibly see my Z column shaking.. My first port of call suggested i break open the coling fins on my controllers and tune my motors with the two purple pots in there to take away the  "harmonic???" ...

having further discussed this issue with Jack, my maufacturer we ascertained that i can rapid at 1150mm/min with no vibration at all...

so...

I only get this vibration when i output a path at those speeds with big tools with big steopvers  (yes even if im only cutting air)..  I can actualy jog at faster speeds perfectly smoothly...  Changing velocity and acceleration change overall zippiness but it stays the same issue once I start cutting a path)

Now.. Jack is a smart and easygoing guy, basically a GREAT guy.. he has suggested that I change the CV (constant velocity)  value away from its current 0.06 to 0.5 and test that rather than start poking around with the pots under the hood...  Jack is a real busy guy and i felt bad asking him to explain to my why this course of action would help...


anyone care to enlighten me? had similar issues?
« Last Edit: August 24, 2009, 05:34:28 AM by Chris.Botha »

Offline RICH

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Re: Not Beef Jerky.. Just Jerky...
« Reply #1 on: August 24, 2009, 06:49:13 AM »
Chris,
I never had any resonance problems. how about going to exact stop and doing a little testing.
Here is the link to info on CV settings       http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

A rather general high level explanation on vibration:
Every thing has a natural frequency. When something either mechanical ( like a tuning fork ) , electrical, even
tool cutting ( chatter ), force from unbalanced object, is at the natural frenquency of another object it will cause it to vibrate. Now once it starts to vibrate and if the exciting forces continue to excite or reinforce the vibration, then the piece can go into resonance. Forces from the resonance can be huge.
So the trick is to eliminate running at or  near the natural frequncy of the object ( or a harmonic of the natural frequency ) and in passing a natural frequency spot you want to go through it so you dont' have time to induce resonance.
The gecko site has some info on mid-band resonance relative to their steppers. There have been some posts on CNC
zone which talk about adding a harmonic balancer to stepper motor.

Exactly which CV setting are you talking about in the Mach3 general configuration?

RICH

« Last Edit: August 24, 2009, 06:55:17 AM by RICH »

vmax549

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Re: Not Beef Jerky.. Just Jerky...
« Reply #2 on: August 24, 2009, 11:14:46 AM »
Chris you have ran into the same thing others have MACHs CV is not up to the task of keeping it smooth . the faster you try to go the worst the fleascratching gets. It is the stop start of the code from line segments or radical direction changes .  MACH does not handle that portion well . SOMEtimes dampers help but it is not the cure justa bandaid.

(;-) TP

Offline Chris.Botha

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Re: Not Beef Jerky.. Just Jerky...
« Reply #3 on: August 24, 2009, 03:46:17 PM »
thanks for the info guys..

so basically the first input I got on tuning the motors via the on-board potentiometers was right too.. different way to achieve same result?

vmax549

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Re: Not Beef Jerky.. Just Jerky...
« Reply #4 on: August 24, 2009, 03:57:04 PM »
NOT nessasaraly, IF we are talking servos the pid settings are to set the servo loop responce. THat has little to do with CV smoothness. IF steppers then you are setting AMPS/Voltage??

THe cv settings tell mach HOW to go about blending all the stop and go moves into a continous motion. IF you start fiddling with the CV you will be able to fine tune a certain RANGE of motion BUT then you may find another RANGE is out of whack. It uselly ends up with you turning all the custom setting back OFF and let mach do its thing BUT you slow down to get UNDER the roughness range.

YOU could aso play with the axis tuning in mach. try slowing the ACCEL a touch to help take the jerk out of it mach uses a Trapezoid curve for trajectory it can be brutal at high speeds on some machines.

Just my experience with mach CV, (;-) TP
« Last Edit: August 24, 2009, 04:03:49 PM by vmax549 »

Offline Chris.Botha

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Re: Not Beef Jerky.. Just Jerky...
« Reply #5 on: August 24, 2009, 04:09:23 PM »
steppers :)

ok, im going to pretend i understood all that and go away now...  ;)

thanks , will digest and poke around under the hood later tonight i hope

Offline Chris.Botha

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Re: Not Beef Jerky.. Just Jerky...
« Reply #6 on: August 24, 2009, 05:30:52 PM »


Exactly which CV setting are you talking about in the Mach3 general configuration?

RICH


vmax549

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Offline Chris.Botha

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Re: Not Beef Jerky.. Just Jerky...
« Reply #8 on: August 26, 2009, 04:15:32 AM »
thanks , got all that.. tested at different cv settings.. does not seem to be making much difference, only gets worse, not better..

going to try the manual g540 tuning

vmax549

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Re: Not Beef Jerky.. Just Jerky...
« Reply #9 on: August 26, 2009, 10:51:42 AM »
(;-) THis is where it usually goes bad fast, BEEN here before, WARNING WARNING Space  family Robinson. LOLOLOLOL

Let US know how it goes, (;-) TP