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z axis loosing zero
« on: December 06, 2011, 01:21:31 PM »
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

Offline ger21

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Re: z axis loosing zero
« Reply #1 on: December 06, 2011, 01:36:06 PM »
Reduce your acceleration by half and see if the problem goes away.
Gerry

2010 Screenset
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Re: z axis loosing zero
« Reply #2 on: December 06, 2011, 01:41:31 PM »
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
Re: z axis loosing zero
« Reply #3 on: December 06, 2011, 03:25:23 PM »
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
Re: z axis loosing zero
« Reply #4 on: December 06, 2011, 03:41:05 PM »
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
Re: z axis loosing zero
« Reply #5 on: December 06, 2011, 03:47:56 PM »
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
Re: z axis loosing zero
« Reply #6 on: December 06, 2011, 03:57:19 PM »
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
Re: z axis loosing zero
« Reply #7 on: December 06, 2011, 04:04:39 PM »
Mechanical/electrical.
 Mid band resonance of the stepper motor.
Re: z axis loosing zero
« Reply #8 on: December 06, 2011, 04:09:32 PM »
You can search the forum for "resonance" and you will find oodles of good info.
Some quite recent.
Regards,
Russ
Re: z axis loosing zero
« Reply #9 on: December 06, 2011, 04:13:04 PM »
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