I would like to build a CNC plasma cutter but am trying to decide if I want to implement a Z axis for THC. I do not have a huge budget to work with, and will be using a hand torch (probably a Hypertherm). The material I will cut will all be flat, but the thickness will vary, I was thinking a manually adjusted z-axis might be adequate to keep the cost down. Just set torch height before you start cutting with a knob and then lock in place with a another clamping knob. I was thinking that since the torch was meant to be hand-held the height must not be THAT cirtical, but then I do no really know. Does THC imporve cut quality, or consumable life, or both? And how much is the improvement?

Thanks!

Typical plasma height controls have initial height sensing for piercing as well as during travel which prolong nozzle life. And the auto height ensures the arc voltage remains constant which also prolongs consumable life. Consistant cut quality is also a benefit.
Also Keep in mind that most CNC tables use a torch that is water cooled due to the usually higher duty cycle of a CNC table. If you cut thin material that is likely to warp with cutting, it may get a bit messy for continuous operation.
Al

If your using Mach2 controller, Campbell Designs has a inexpensive THC that works with Mach2. I haven't used it myself but for the money it may be worth a try.

Torch height control is essential.
First- heat makes metal warp. Especially thin strips of metal- it is not unusual for a 1/4" wide strip of offcut to warp 3 or 4 inches up in the air. Then your torch hits it, crashes, and of course your registration is shot. Ruined work, start over. Thin material will warp up as much as an inch or so just from the heat of cutting- Thicker material, say 1/4" and up, will usually not warp as much for cuts in the middle of the piece, but as I said, thin strips of 3/8" or even 1/2" can warp up sometimes.
And the whole point of an automated machine is to let it run unattended. Takes all the fun out of it if you are constantly having to manually run the torch up and down.
And then, with torch height control, you can cut curved surfaces-which is nigh on impossible manually.

I would hate to be without automatic height control on my cnc plasma table. Far too often thin metal warps with heat and can cause a crash or drag that lwill lose location and therefore scraps the piece. Also I often cut metal that is not perfectly flat, sometimes salvaged metal, sometimes second grade. My unit uses prox sensors but I am thinking about a change to arc voltage sensor system. If finances don't allow the auto stuff then build a carriage that will allow you to raise and lower it with a switch on a cord. Don't make the mistake of thinking you can lean over the table and do it manually. It just isn't safe or efficient.
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