Plasma Torch and Z Axis

[krazycnc]

Am on the verge of buying my first torch - Hypertherm Powermax 380 - and don't quite understand how to controll the cutting process. Using Sheetcam there are settings that allow initial pierce height, delay and rapids height adjustment. I guess my question is will this particular model have to contact the work surface to start the torch, raise up (1/8 - 1/16in.) for cutting height, stop and turn itself off (software controll?), move to the next cut and recontact the cutting surface or how does this go? I actually have my Z axis built with stepper motor controll (2-1/2in. travel) and am working out limit - home switches on it right now. Could I just use a switch on the Z Axis to replace the hand torch switch?

Thanks in advance

[rboeser]

Did you research the THC (torch height control) available from Bob Cambell? (I think thats his name)

It looks very good and sounds like its exactly what is needed to control the torch height, evan for cutting an uneven sheet. It will raise and lower the torch to mantain the arc voltage for cutting.

Search the 'Zone for THC, or google it. You will know when you find it.

[DCparts]

They have to touch the material for the THC to work properly. It touches the surface and samples the voltage at the correct height and then adjusts the z accordingly.

I'm not sure about your particular system, but I don't have to program any of the Z axis moves in the CAM software, those settings are controlled by the control. So the machine touches the surface, raises tip pierce height, moves to cut height, performs cut, the moves to the next hole and touches the surface and starts again. But you can program it to only touch once within a certain area, like a 5 inch radius, or you can have it sample the voltage every pearce.

You can hook the torch switch into the control and use a M code to turn it on and off (M11, M21 for mine)

[krazycnc]

Thanks I'll do some more research, just trying to get a feel for the 380 and how it all works together. I was thinking not everyone has THC hardware and how do they go about it.

[Scott V]

Originally Posted by rboeser Did you research the THC (torch height control) available from Bob Cambell? (I think thats his name) It looks very good and sounds like its exactly what is needed to control the torch height, evan for cutting an uneven sheet. It will raise and lower the torch to mantain the arc voltage for cutting. Search the 'Zone for THC, or google it. You will know when you find it.

http://groups.yahoo.com/group/CncMan...yguid=82702294

Tom Caudel at the yahoo site will clue you in. He worked with Bob and others to perfect his THC.

The z only needs to touch to reference the sheet, and does not use arc voltage for that. Tom will help you out, along with Les from Sheetcam.

Scott

[anthony]

when i first built my plasma table, i didn't have the thc.
if you want to go low-tech, you'll at least need
some way to raise and lower the torch to get it out of harms
way. not to mention, its best if the torch is coming down when the
cut starts.. that it doesn't turn on when its at pierce height. you'll
go through alot of consumables that way.

that said, i didn't run very long without getting the THC from tom&bob.
great product, well worth every cent.

you'll need another stepper for the Z axis.. and you'll have to "spring load"
your torch and switch. basically the stepper starts to lower your torch, the torch
makes physical contact with the metal surface (the stepper is still pushing) but
the torch is riding on a spring (like a shock absorber) and stops moving. for an
instant you'll have a situation where the motor is moving down, but your torch
has made contact and is not moving. at that point the back (or some part) of
your torch trips a switch.. and tells your control software that you've hit Zero.

its much simpler than i may have made it sound.
once your software knows where zero is, sheetcam comes into play, and
will raise it to your Pierce Height. the torch comes one, and sheetcam (=gcode)
will slowly lower your torch (at an angle, "ramp") until it reaches your set CutHeight
(which is lower than your pierce height, of course). once your at CutHeight, the
torch begins to move. within the first 1/2" the THC already starts to measure your
torch height, and adjusts it accordingly, up and down, within limits that you can
specify.

-anthony

[krazycnc]

Thanks Anthony,
As I go along learning what it really takes to do this I am reminded of the fact that if you are going to do this "Do It Right" and thats what I did, I got Mr Campbell's THC-300, Sheetcam, Mach2-3 and a separate Z-axis control motor. I am right at the point of designing the "floating" Z-axis and reading and understanding all the info from everyone and putting it all together! Didn't realize what a big bite I bit off.