I was thinking about building a cnc plasma cutting table.I would like to do it on the cheap.I was thinking for the X axis use roller blade bearings with angle iron.Then on the Y axis use round linear rail with cheap bearings.I have the Z axis already built ,for the most part.It has a floating leadnut with a spring behind it.So when you set your torch one eighth off the material if it starts to warp the torch will drag, but the spring will be loose enough where the torch just floats on the metal.I am thinking of useing a soleniod to pull the trigger on the torch.It will be activated by the spindle ON relay.


Does anyone have any other ideas they would like to add. :stickpoke

Just so you know I have already built a CNC Router.

Thanks

You will kill the tips if you drag it with any pressure on the plate.

Not with the HYPERTHERM 380! It was designed to drag!

Can't you use the relay to switch the torch trigger direct without the mechanical in-between of a solenoid?
Most are just a single contact closure switch. Find out where the switch wires end up in the plasma box and wire the relay across them.
For something to do this winter I think I am going to complete my plasma table, I have the Y axis driven by a kevlar timing belt.
Al

I own a 380, and I said if you drag it with any PRESSURE you will destroy the tip. The tip is much softer than the steel plate. After a few feet the kerf will be an oval shape, not bad for straight lines, but sucks for circles.

So it depends how you define "any pressure", springs don't have to be strong.

What about adding some casters around the head? :)

Anyway, if you look at the torchmate stuff: http://www.torchmate.com/ you will see that for guides they use cold rolled flat steel and bearings although perhaps not rollerskate ones. There are enough pictures on the site to get the idea. This seems more than good enough for plasma.

Graham

They use cam follower bearings in their setup, oh so handy with the studs and all.

Its much better to have no physical contact between the torch and the work- for one thing, lots of times I will be cutting a piece out of scrap- and if the scrap piece is small, like a piece I threw on the table today, then the torch could easily push it along- throwing your cut off completely. Then you would have to clamp down every piece of metal you cut- big problem. And as you finish the cut, and the part comes loose, then your drag spacer will drag it right along. Then you will sometimes cut holes or lines in your freshly cut part- I can see more and more reasons why this is mucho big pain.
My machine has a feedback circuit that senses torch voltage, and adjusts torch height with a z axis motor, and believe me, I would never live without this feature. The thinner the material, the more it warps as you cut it- my machine has 4" of vertical height range, and there are times when it uses most of it. As you cut thin strips of something like 14ga, they will peel up into space, sometimes sticking up 6" or more- guaranteed to run right into your spacer. Auto torch height also allows you to cut things like expanded metal, which your device would go crazy on.
And to cut curves out of big pipe- with my 4" of z travel, I can birdsmouth pipe with no extra jigs.

I do not think there is a way to make it work the way you described.Maybe you should buy one from someone that knows what they are doing!

Good points, Ries. After cutting 26ga polished SS on my rig I really saw the torch height controller do it's thing!

Generally speaking, CNC machines do not drag the torch across the surface like a standard hand torch with shielded consumables. You might want to look and see if your plasma torch has non-shielded consumables available for it. Ideally you want to touch off on the plate and make and arc, then pull up about .25", pierce and move. The torch (with Z axis THC) will hover above the material at .25 and maintain that distance by checking the voltage of the arc and adjusting the Z accordingly.

In many cases, you need to have the I/O board installed for use with a THC from the manufacturer so that your THC interface card can talk to the plasma cutter. There's a LOT more to it than meets the eye. You'll need to control arc voltage and reliably turn the torch on and off.

-Brady

hey jim did you ever get to try the solenoid for the torch trigger?

I am just getting to that point with my router conversion

dont need anything as fancy as THC for what i am doing right now
and dont want to hack into the plasma cutters wiring for an occasional use
thing. solenoid off of the router's motor start relay seems like a perfect fit for the design intent.