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plasma probing routine
« on: April 07, 2011, 09:19:00 PM »
i cut a lot of hr steel , mostly 12 ga. to 16 ga. multiple parts nested to use all of sheet, sheet sizes 144x72. i have the z jog to +3 before moving to the next cut. then jog to +.5 to begin the probe for surface before firing the torch. it all works well except if the next cut is at a buckled area of the sheet. sometimes the sheet will oilcan up as much as 1 ". during the probing routine the torch will touch the sheet before it has moved to the commanded position of .5 above the sheet.when this happens mach goes into a loop and
stops movement. what i would like to happen is the torch is moving down rapidly, if encounters the sheet before .5 " retract 1 " and then attempt to probe again. is this possible? anyone tried it? would it require a brain, or a macropump?

Offline BR549

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Re: plasma probing routine
« Reply #1 on: April 08, 2011, 04:08:53 PM »
Depends on what type home sensing solution you used on the Z axis. The safest way I have found is to create a fast probe solution and KEEP the head well above the problem height when in rapid movement.

Stay at your safe +5 inch height then do a rapid probe down to find the surface then raise .5 inch above that point and reprobe in slow mode for a more accurate height setting.

Trying to probe while in XY rapid can work but also can tear off your torch head if it strikes a riser in the plate to be cut and catches the torch head.

Now IF you are using an independant height sensor this can work IF the sensor is lowered to a height that is lower than the torch head then retracted when done. You would use a G31 probe move to rapid to a new start position. You will have to set up the Cam post to input the code correctly.

Been there done all of that. Those little fiberglass sleeves that break to protect the head are $90 each.

(;-) TP
Re: plasma probing routine
« Reply #2 on: April 09, 2011, 09:17:33 AM »
You retract to 3 inches and the torch is crashing on rapids because of warpage?  We cut 20ga, 16ga and 12ga all day long.  I have safe Z set at .5".  That means that when the torch shuts off, it retracts to .5" and moves to the next start point, probes and starts the next cut.  These Z moves are relative to the work piece as the THC keeps the torch at set height above the work.  I use G31 for probing, not G28.  I'm not sure why you are needing to command a rapid down to .5" before beginning the probe...or more to the point, why you have the need to raise the Z so high for rapids.  You should be able to retract to safe Z (.5" or less), move to the next cut and call a G31 to probe for the next pierce height. 

You shouldn't be getting that much warpage on 16ga and hardly any at all on 12ga.  What are you're cut speeds and plasma power settings?

"Stay at your safe +5 inch height then do a rapid probe down to find the surface then raise .5 inch above that point and reprobe in slow mode for a more accurate height setting."

Maybe I don't understand the problem.  Why would you need to retract to 5" for rapid moves.  Moving up and down 5" at each cut would take forever on multiple nested cuts.  Even on 24ga steel, I've not seen more than about 1" of warpage and that's rare.  There is only one part we've done where the Z range was about 4".  On this part, I had to bump safe Z up to 4.5".  This was not because of warpage, it was due to the shape of the base material being cut.  even then, if the Z was at the 4.5" rapid height and the cut was at 0", the G31 just probed down to the material.  No need to command a rapid down before beginning the probe routine.

Offline BR549

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Re: plasma probing routine
« Reply #3 on: April 09, 2011, 11:23:16 AM »
I guess you have never hung the torch on a riser edge and ripped the torch head off on a rapid????

I have seen stable plate and plate that would warp like a pretzl.

The idea of the fast probe  from a high safety height is to speed up the process.

BUT if you don't have the warpage problem then you don't need the advice(;-)

Just a thought, (;-) TP
Re: plasma probing routine
« Reply #4 on: April 09, 2011, 02:13:30 PM »
I've had crashes, but always as a result of a mistake in the program (IE: Not retracting to safe Z before a rapid)

My point was that we cut 16ga and 12ga all day long and 12ga hardly warps at all.  16ga is marginal...1/4" warpage at the most.  I'm not using special steel.  Just plain old run of the mill HR.  In 10 years of doing this, I've never needed a safe Z of more than 1/2".  The best way to speed things up is to not retract to 5" for every rapid, but rather figure out why there is so much warpage that 5" is required.  Even at rapid speeds, that's a lot time when you're doing it on every arc start.