Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: kimfmx on December 06, 2011, 01:21:31 PM
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Ok it started when i was milling a series of letters with a v-tool using V-Carve from Vectric, and i notised that the letters were gradually getting deeper and deeper, first thought the land had shifted so i regrounded it, but the problem was still there... so i made a copy of the G-Code, and isolated one letter, and copied it after eachother so it effectively made a "A" over and over again at the same place, and yes it did very slowly but surely go deeper and deeper every time it made the letter. even if i with all my power tried to pull the z-Axis upwards while it was making the letter i still see the problem.... I do NOT believe its loosing steps mechanically.. i have been running this machine for a long time without problems, and even at half motor current, now I have ramped everything up to max, and i still see the problem...
So the sympton is directly visible as when.
Zero the tool at top of material.
Run multible "A" letters over and over again, and can hear that its grining on each downwards cut which it shouldent..
stop, Place the tool at top of part again, now Mach3 says its 2 mm above the part!!!
I notised that when i slide the FRO override up and down, i can make the problem appear and disappear??
I made a simple G-Code program that just simply excersized the Z-Axis up and down fast for a long time, and that worked flawlessly...
Im using Mach3 to drive the motors, the program that generated the G-Codes was vectric, using the MACH2/3 ATC [mm] postprocessor, i have plenty of power on my motors, and they do not stall, even if i hang on the z axis while its going up. Im using Mach3 3.042. The motor Driver is HobbyCNC product.
I moved the setup to a smaller CNC I have, and run the same program, and I see the same behavior?
Any help is much appriciated...
Best Regards
Kim Mortensen
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Reduce your acceleration by half and see if the problem goes away.
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Yes sorry I should have mentioned this.
- I reduced the acceleration from 200 to 50 on all axis.
- Enabled the Sherline pulse compatibility
- reiwired the motoros so I did not use the ActiveLow setting in the port/pins configuration for motor direction.
And its still doing it.
Regarding the FRO. When I put the override high it seemed to perform forrectly, but lowering it to like 50%, it would make cuts in the material on every downwards going motion, eventhoug it was exactly the same as before..
I upped the amps on the motors, decreased their max speed in MACH3.. still doing this..
As i havebeen cutting wood most of the time i have not taken too much notis of this as the wood would be different size, and maybe my plane is not 100% level, but now i have reground it also..
Best Regards
Kim Mortesnen
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Hi Kim,
There were very similar happenings to yours in the past that were contributed to pirated Vectric software.
Are you sure yours is genuine ?
You could verify with Vectric to be sure.
Russ
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Russ,
I should very much be genuine..
But if its possible to feed MACH3 a set of G-Codes to make it loose track of where its tool is, then i would surely think its Mach3 that is faulty..
- zero the tool at the top of part.
- Run the Vectric code.
- return to zero, now the tool is 2 mm into the part.
That can not be because of vectric code.
Best Regards
Kim Mortensen
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It could very well be, Kim.
Just seems strange that it is the SAME on an entirely different machine ... what a coincidence.
I moved the setup to a smaller CNC I have, and run the same program, and I see the same behavior?
Best Regards
Kim Mortensen
Are they steppers ? You might be in an area of resonance.
Regards,
Russ
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True.
It is steppers, and i have not heard about resonance issue before, but the thought could make sence as when changing the FRO, the frequenceys change.
Are we talking mechanical/electrical or software resonance.
Best Regards
Kim Mortensen
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Mechanical/electrical.
Mid band resonance of the stepper motor.
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You can search the forum for "resonance" and you will find oodles of good info.
Some quite recent.
Regards,
Russ
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ok, interresting,
so in case of resonance, i just read that faster acceleration "may" lower the properbility of an issue, which makes sence as it will spend less time in the resonance zone.. and also when I moved the FRO Down, is moved further towards the resonance area..
So my big question is what can i do about it. The X and Y Axes are coupled using lovejoy couplings, where the Z axis is using belt drive. are we talking some sort of aditional dampening on the z axis.. or how do I obtain this "viscous dampning" effect.
Best Regards
Kim Mortensen
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You will find many MANY references in the forum search.
Mechanical dampeners/dampers are the norm.
Gecko drives takes care of it electrically, in their drives. Thats where the earlier reference came from.
If, in fact, your problem is mid-band resonance.
Russ
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Russ,
Thank you, i did do a search, and suddenly it went fast.. with youtube videos etc... logically the Z axis is the only axis that is not connected through a lovejoy coupling, but a belt drive, so the properbility of this beeing the issue is indeed high when taking all the other symptoms into consideration...
Thank you very much for your help, ill arrange for a damper to be made, and redo some tests.. and let you know if it fixed the problem.
Thanks a mill..
Best Regards
Kim Mortesnen
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I wsh you the best outcome and will watch for your report.
Regards,
Russ
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stupid question, but how old is your mach3 version?
I remember a point in time when mach 3 FRO would actually try and get the machine to move faster then the motor tuning settings. Caused me a lot of headaches in the beginning. But that has been YEARS ago.
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The Mach version im using is Mach3 3.042
I did try and look at the changehistory on mach site if there were bugfixes that could persuade me to tear down the installation, and upgrade to a new one.. but couldent see any bugfixed in this are.a