Plasma Torch Voltage ?

A friend is building a Plasma Torch Cutting Table. He will be buying the a CNC control electronics kit for the X Y axis.

I would like to build a torch height controller to use with the table. The computer end of this should not be a problem for me.

A few questions that you may be able to answer:

What voltages can I expect to find between the torch and the table/work?

What is the polarity of the same? Is it steady DC or pulsed ?

Is there anything else I should know?

I wouldnt waste your time. Bob Campbell has one that works with Mach 3.

http://www.campbelldesigns.com/plasma-torch-height-control.php
$390 for everything in a box including the voltage divider for the plasma.

Also Rutex makes a more of a stand alone version:
http://www.rutex.com

OCV on plasmas can be up to 350vdc. Operating voltages are usually around 100vdc. Then there are issue like corner dip, touch off, ect. Its not as simple as you think.

$400 is not unreasonable.

I was not under the impression it was easy. The setups I had found on the web were over two grand.

Thanks for the help.

Is your friend using Mach 3 to control the table?

So far he has the mechanical plans for the table. He told me what software he intended to use but it did not stick. I got the impression that he did his research but it may be darted in that he could not find an inexpensive torch controller.

At this point I am sure Mach 3 is a possibility since it is inexpensive. Whatever works well and provides good bang for the buck. Suggestions ?

I provided him with a printout of this thread so we may see him here sooner or latter.

I would go with something like Geckodrives G320 servo drivers to run the three axis. I dont like steppers. You can loose steps. Servos have encoder feedback so there is no lost steps. Use a rack and pinion system. Depending on the size of the table maybe two servos on the long axis (X). You can either belt them down or use a gearbox.

I like Mach 3, thats what I use on my mill. Support is good and quick and you cant beat the price. There are a few options for interfacing to the table, First is the parallel port. This is the cheapest option and lowest performance. But this is where you will want to start for now at least.

Second is the ncPod. This is a little board that is connected to your PC via the USB. It has a small microprocessor on it and sends the signals to control your motor drivers. It is still in beta stages and it does not offer much higher performace in step frequency above the parallel port.

Third is the Geckodrive G100 "GRex". This is a $400 6 axis motion controller that talks to mach through a ethernet cable. This is what I have on my mill. It has the best performance with a 4Mhz step freq (VS 45khz on the others) With this I am driving my mill at 50000 steps per inch at 400ipm. It is also in beta right now but is progressing rapidly literally weekly.

For him right now I would stick with the parallel port as I am not sure if you can use the THC with the ncpod or the grex. He will need a decent computer to run it. I use a 2.4Ghz P4 with XP Pro.

Build your machine nice and rigid. This way you can stick a router spindle on the z in place of the torch and play around with wood.

Get a larger plasma than you think you are going to need. Most plasmas are rated at about a 60% duty cycle and a plasma table will run it to 100%. Figure a machine rated 1" will maybe do 1/2" on a plasma table. Use a machine torch. Dont mess around with those jury rigged holders that hold a hand torch. Buy hypertherm if you have not picked one up yet. Best darned machines out there.

Last, check out http://www.cnczone.com This is the home for CNC related stuff. All sorts of people making machines out there.

Eugene,

Please take a look at this link.

http://www.candcnc.com/

Tom Caudle is a nice guy and will provide you with some great advice.

Good luck,

Tom