My Newb Plasma Table Attempted Build

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16 May 2020 10:11 #167944 by tommylight

it seems your Z axis is loosing position while working, can you try setting a lower probe speed, please ?


It only does this when THC is enabled. When THC is disabled it never does. I can try it, willing to try anything to make it work right.

Should have said lower all Z axis speeds, by half, just to be on the safe side.
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16 May 2020 10:29 #167946 by phillc54

It only does this when THC is enabled. When THC is disabled it never does. I can try it, willing to try anything to make it work right.

Could you do a short cut with THC disabled and the material ramping down slightly as the torch moves. So the material should be closer to the torch at the start then further away at the end. Can you observe what the arc voltage does as the cut progresses. Maybe then do another with the ramp opposite, so finish closer than the start.
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16 May 2020 15:48 #167977 by dvn4life1972
I did the cut from the higher side (closest) first, 4in long. Once the arc voltage stabilised it started to increase as the work piece got farther from the torch tip, and the opposite going the other way (eventually touching the workpiece at the end due to no THC).

Pat

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16 May 2020 16:45 #167979 by tommylight

I did the cut from the higher side (closest) first, 4in long. Once the arc voltage stabilised it started to increase as the work piece got farther from the torch tip, and the opposite going the other way (eventually touching the workpiece at the end due to no THC).

Pat

Did the torch move at all down for the first case and up for the second ?

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16 May 2020 16:56 #167981 by dvn4life1972
I had the THC disabled, Phil requested the test with it off. I can do it again with it on. It usually doesn't dive until after a long run though (somewhere beyond 12 or more inches of linear cutting travel).

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16 May 2020 17:02 #167982 by tommylight
Again, did the torch move up or down during that test?
What were the readings on voltage display during that ?
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16 May 2020 17:20 #167986 by dvn4life1972
The torch did not move up or down. Pierce was about 185v, then moving from high/closest end to low/farthest end it started at 140v and ended at 155v.

Going the opposite direction it started at about 144v (after pierce) and dropped to about 138v by the end when it was physically touching the steel

Pat
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16 May 2020 18:46 #167993 by tommylight
That all seems very reasonable, so that is good.
Can you do a dry run of some gcode with at least 20 to 50 probes/piercings and note when it happens and what exactly happens ?

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16 May 2020 22:28 #168009 by rodw

I did the cut from the higher side (closest) first, 4in long. Once the arc voltage stabilised it started to increase as the work piece got farther from the torch tip, and the opposite going the other way (eventually touching the workpiece at the end due to no THC).

Pat


So this just confirms arc behaviour where arc voltage increases about 10 volts per mm change in cut height.
Or in my test on one plasma cutter it was 7.53 volts/mm over 16000 readings.

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16 May 2020 23:21 #168012 by phillc54

I did the cut from the higher side (closest) first, 4in long. Once the arc voltage stabilised it started to increase as the work piece got farther from the torch tip, and the opposite going the other way (eventually touching the workpiece at the end due to no THC).

Well that seems to behave correctly, I have no idea why it would decide to drive the torch down, maybe noise or moon phase.
You will probably need to set up halscope and hopefully we can see what is happening.

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