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Jerking motion and slow down while cutting

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Ribbedgiraffe
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Jerking motion and slow down while cutting

Postby Ribbedgiraffe » Tue Oct 11, 2016 11:38 pm

Good evening everyone, I'm having an issue with My table and I'm assuming it is a Mach 3 setting I am overlooking.

I'm getting a Jerky (shaky at times) movement on my table. The part that is really confusing me is, It only occurs while I'm actively cutting. While it is going through this motion my travel speeds also slow way down, If I'm cutting at say 58ipm it will display speeds all the way down to 13ipm... I Thought it was a power supply issue as I was running a slightly undersized supply. I assumed the difference between a dry run and while cutting was the THC is active and moving the Z axis while underway. Last night I upgraded my power supply and saw no improvement.

Has anyone else seen this type of issue?
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acourtjester
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Re: Jerking motion and slow down while cutting

Postby acourtjester » Wed Oct 12, 2016 8:25 am

One thing that changes is the power consumed when cutting your adding the plasma cuter and the compressor.
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Ribbedgiraffe
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Re: Jerking motion and slow down while cutting

Postby Ribbedgiraffe » Wed Oct 12, 2016 11:13 pm

My voltage doesn't appear to fluctuate, I have a voltage/ammeter on order to monitor the volts and amps while cutting. Using the fluke, the voltage holds strong at 48 while cutting. The compressor runs very little during any of my tests. I run 2 40 gallon tanks to try to limit the amount of starts/stops during cutting.
Still learning!

4x8 homebuilt w/Water table - Hypertherm Powermax 45 (Machine torch)
13" Metal Lathe
7x12 Meta lathe
1-1/2hp Milling machine
Hobart 190 Wire feed
Hobart EZ-Tig

Elcheapo powdercoating gun W/Autoclave oven converted for powdercoating.

Ribbedgiraffe
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Joined: Tue Mar 15, 2016 3:03 am
Location: Washington

Re: Jerking motion and slow down while cutting

Postby Ribbedgiraffe » Thu Jan 12, 2017 1:57 pm

So - I'm still working through this jerking / shuttering motion.
No power issues, It doesn't have the issue if the THC is not active. Is it possible this is some kind of EMI interference? I have ordered new Shielded Cat7 Cables for my THC (It currently has Cat5 cables that I suspect may be unshielded, I literally pulled them out of my computer drawer.... ) Also - My torch lead is inside the same cable track as my motor wires, This issue ONLY shows when the Z axis is active and using THC So I don't think that is the case..

Thoughts?
Still learning!

4x8 homebuilt w/Water table - Hypertherm Powermax 45 (Machine torch)
13" Metal Lathe
7x12 Meta lathe
1-1/2hp Milling machine
Hobart 190 Wire feed
Hobart EZ-Tig

Elcheapo powdercoating gun W/Autoclave oven converted for powdercoating.

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SeanP
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Re: Jerking motion and slow down while cutting

Postby SeanP » Thu Jan 12, 2017 4:28 pm

I have the torch lead in the same track as motor cables, no problems with that on mine.
Have you tried looking at the thc rate on the settings page I think it is, that can make the z axis judder.
Span gap in cut profile I set to 5/4volts for thicker that 10mm again to stop judder.
You system maybe different, I am using Mach 3/ parallel port.
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Ribbedgiraffe
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Re: Jerking motion and slow down while cutting

Postby Ribbedgiraffe » Fri Jan 13, 2017 2:23 am

FINALLY!! No more jerking and shuttering.. thank you!


Now, new problem, after the first cut finishes, the torch dives into the work piece, not sure what the heck is going on now... ugh... always something..
Still learning!

4x8 homebuilt w/Water table - Hypertherm Powermax 45 (Machine torch)
13" Metal Lathe
7x12 Meta lathe
1-1/2hp Milling machine
Hobart 190 Wire feed
Hobart EZ-Tig

Elcheapo powdercoating gun W/Autoclave oven converted for powdercoating.

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SeanP
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Re: Jerking motion and slow down while cutting

Postby SeanP » Fri Jan 13, 2017 2:38 am

You need to be turning off thc for holes less than 30mm, and 12mm or so before the end of the cut, I use the cutting rules in sheetcam to do that, holes are probably your main problem with that I would imagine.
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tcaudle
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Re: Jerking motion and slow down while cutting

Postby tcaudle » Fri Jan 13, 2017 11:50 am

When your torch ends the cut look at the Z DRO. (Feedhold if you have to and measure) Is it where the TORCH actually is? Do you have a touch off sensor? The motion under THC on a MACH3 based THC can result in lost steps if the THC Rate is too high or the Z itself is tuned too hot for the Z's ability.

Diving into the plate is either from the Z losing steps and it being lower than it thinks it is, or the THC is turning on too soon during a pierce and diving based on the voltage spike

Keep telling yourself: The Z moves opposite the Arc volts to try and make it be what you have set for the Preset. If the volts are too high it dives the torch to LOWER the volts.

Ribbedgiraffe
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Location: Washington

Re: Jerking motion and slow down while cutting

Postby Ribbedgiraffe » Fri Jan 13, 2017 2:23 pm

Ill play with the THC rates tonight, I suspect this has something to do with it as it was also what appears to have fixed my shuttering issue.

The confusing part - Say for instance I am cutting a square, after the cut sequence is complete the torch shuts off and dives into the work. If I am cutting multiple squares, after the first part is cut it does the same thing, Finishes the cut and dives straight down AFTER the Torch is shut off. It seems like an odd reaction to a THC rate change. I even pulled some old Tap files to be sure something didn't "magically" change in my post processor.
Still learning!

4x8 homebuilt w/Water table - Hypertherm Powermax 45 (Machine torch)
13" Metal Lathe
7x12 Meta lathe
1-1/2hp Milling machine
Hobart 190 Wire feed
Hobart EZ-Tig

Elcheapo powdercoating gun W/Autoclave oven converted for powdercoating.

tcaudle
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Re: Jerking motion and slow down while cutting

Postby tcaudle » Fri Jan 13, 2017 4:50 pm

Observation is your best tool
Its important to watch the Z DRO a the end of a cut when this is happening. It is supposed to lift UP from the G-Code to rapid height/ If its going down and the DRO shows it going down something is telling it to move in that direction. If its going down and the Z dro is not tracking with it then either the motor cannot move that fast and its reversed its direction of motion (severe motor stall) or the DIR bit is flaky out of the controller .

If the Z has lost enough steps and it thinks its way UP in the air (and its not) then when the software says to move to rapid height it thinks it needs to go DOWN to rapid from where it THINKS it is.

The Z DRO is your key

THC rate COULD cause loss of Z position and cause the software to think the Z is much higher than it really is

Ribbedgiraffe
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Joined: Tue Mar 15, 2016 3:03 am
Location: Washington

Re: Jerking motion and slow down while cutting

Postby Ribbedgiraffe » Thu Jan 19, 2017 11:19 pm

Well, after watching it crash a few times I realize it is missing steps. The Z DRO does appear to stop tracking while this occurs.

If I set the THC Speed to 55 or less it does not crash, but shutters like crazy and makes sh*tty wavy cuts (Worse now that I've sped up my Z). If I bump the THC speed up to 70 and above the shutter goes away but it crashes at the end of the cut. I've got my Z running as fast as it will go without stalling, Is it time I upgrade the motor on my Z?
Still learning!

4x8 homebuilt w/Water table - Hypertherm Powermax 45 (Machine torch)
13" Metal Lathe
7x12 Meta lathe
1-1/2hp Milling machine
Hobart 190 Wire feed
Hobart EZ-Tig

Elcheapo powdercoating gun W/Autoclave oven converted for powdercoating.

tcaudle
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Joined: Tue Feb 28, 2012 6:47 pm

Re: Jerking motion and slow down while cutting

Postby tcaudle » Fri Jan 20, 2017 3:33 pm

What are you calling "THC Speed" Is that the name on your screens? Its called THC Rate by MACH and its a percentage of max Z velocity. Of you are running at 55% , the Max Z velocity your velocity would have to be no more than about 60 IPM . You simply cannot make MACH move the Z in THC mode very fast. It gets completely instable and causes up and down oscillation. The slower the THC Rate the slower the osciallation. If you make it high evoiughe it will simply sit and vibrate or even refuse to move the motor at all.

Upgrade the motor? You might get a little more speed on the hign end if you put a higher torque motor but al lot depends on the Z mechanics.

With virtually no information as to the electronics and HOW its being driven (parallel port. Ethernet, ?) or any info on the THC , the motion problems are not going to be easily resolved.


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