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I have a few questions on general CNC plasma operations

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I have a few questions on general CNC plasma operations

Postby Econdron » Mon Jun 26, 2017 2:52 pm

I have a 5x10 table, Precision Plasma 8020 HD gantry, CandCNC full automation bundle with CommandCNC for the electronics. HT 45XP for plasma. Only have a couple weeks of experience, so go easy on me!

Question #1 - I went to cut out a dino head (see attached picture) out of 14ga MS, actual size, each row of teeth is about 2.5" long, so it's not crazy big. The velocity anti dive pretty much keeps the DTHC off during that whole row of teeth, but the warpage in the sheet has caused the torch tip to start dragging by the time it gets to the end of the teeth. Does anyone know any ways to work around problems like this? I can't think of anything other than having it stop halfway through with a lead out, then have a lead in come back and start it where if left off, that would allow re-adjustment of the z-axis without the DTHC. If the velocity anti dive is turned off, the torch just dives during the cut. Cutting at 225 IPM with standard consumables.

Question #2 - Sometimes I have a hiccup during a cut, and the torch dives, or I need to change the consumables, or whatever. Is there a way to pickup again where I stopped the program? If I hit pause, I can't jog the system, which I usually need to do. But if I hit stop, it restarts the program. On smaller parts, I just disable the torch until I get back to where I was, then turn it back on, but on larger parts I don't have the patience and usually just start fresh somewhere else.

Question #3 - I was cutting some brackets out of 12ga the other day. Large enough where I didn't need a holding tab. At the end of the cut, the torch would dive. I set a rule in Sheetcam to turn DTHC off .15" from end of cut. But .15" from the end of the cut, the torch stops moving, then starts again, like there's a pause in the G-code. It does turn the DTHC off though. And it's set to leave the travel speed at 100%. There was another time I was cutting some parts out of 3/8" material, and had a .25" leadout, so I set Sheetcam to turn off DTHC at .5" before the end of the cut (including leadout) and the DTHC turned on again after it turned off. I'm assuming there was something with the velocity anti dive that turned it back on. Any help on this one?

Thanks in advance!

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Re: I have a few questions on general CNC plasma operations

Postby motoguy » Mon Jun 26, 2017 4:53 pm

1) You could lower your VAD %. Default is 85%. Lower % decreases VAD "sensitivity"; THC stays on, torch might dive at corners. Increasing % increases VAD "sensitivity"; less time THC is active, but also ensures torch won't dive. I'm surprised, though. Those teeth (at 2.5") seem large enough that I'd think VAD would handle them just fine, and still keep THC active during most of the cut. You could resort to good old "on corners" rules in sheetcam, to turn THC off altogether at the corners. I wonder if there isn't something else going on, though.

2) Hit pause, so stop movement without losing location. Then hit "stop'. THEN go back to the M05 command prior to the part/line you are cutting. Select that line, and click "run from line", or "start from here", or whatever it's called. The torch will go to the beginning of the most recent cut/part, and start from there. If you don't need the torch on to begin with, you can click 'disable torch' to keep the torch from firing, and 'disable hold' to allow the torch to touch-off and move without the ARK OK signal. Once the torch is moving along the cut path, de-select the "disable hold". Once the torch gets close to the point where you had your issue, you can de-select "disable torch", and the torch will fire.

You may need to select "THC MANUAL" during this, to keep the torch from diving when it fires. If so, wait until it has cut into fresh metal a little bit, then click back to "THC AUTO".
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Re: I have a few questions on general CNC plasma operations

Postby tcaudle » Tue Jun 27, 2017 2:45 pm

A lot of this has to do with the capabilities of your tab;e and its settings. here is how the trajectory planner works in LINUXCNC:
It looks ahead at the toolpath and says "Can I make those moves at the current velocity and acceleration settings" If not it gives preference to accuracy (toolpath tracking ) and slows the motion down to be able to track accurately. This is the way you would drive a racecar on a closed circuit where you had to stay as close to raod as possible. The VAD senses the slowdown and turns of the DTHC unitl the velocity gets back to the full amount. It is very fast. To make it less sensitive (stays on longer) as motoguy said you lower the % so it has to slow down a lot more before it turns it off. The other thing to look at is the actual tuning of your motors. The less aggressive the max velocity and acceleration the more forgiving of the toolpath beacus it might be able to make the moves without slowing down. You might try lowering the XY acceleration numbers if they are above 35 ips/sec.

The type of DTHC OFF you use is important. There ar two types . One justt urns off the DTHC no matter what and should not be used in the middle of a motion line. The other (different M command) is an "inline" command that executes it DURING the next XY move. The static ON-off is am M68 where as the dynamic is an M67 . In most circumstances you use the M67 version but it won't execute until it sees a X or Y move so it could be delayed

The VAd is based strictly on the current sstate of the DTHC (enable or disabled) and the actual velocity of the toolpath at that instant. Its disabled if the DTHC is disabled , or the torch is off or if the actual velocity is less than the commanded velocity.

D-chit Worx
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Re: I have a few questions on general CNC plasma operations

Postby D-chit Worx » Fri Jun 30, 2017 4:24 pm

i just started using the plasmacam and i cant get the torch to fire when it starts cutting ......any tips

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Re: I have a few questions on general CNC plasma operations

Postby tcaudle » Fri Jun 30, 2017 6:00 pm

You might try asking over in the PlasmaCAM forum on this site under the Plasma Machines section.

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