[racerunner]

I’ve recently started working at a school on the Gold Coast that has a plasmacam dhc2 in the corner of the workshop – not being used. I’m told a past teacher strapped on a wood router, it didn’t work, and now nothing works. We would like to get it working as a plasma machine so that our shop students get some experience with it. None of us is familiar with CNC so we need some help to get the machine back in working order.

We have had a plasmacam rep come but because the machine is old it was going to cost an arm and a leg to update software and the yellow box. We’re currently waiting for another expert to come and tell us what is missing on the machine and assure that it has all its bits – but we don’t seem to be detecting much enthusiasm from the person concerned.

Do you know anyone who can help us get our plasmacam dhc2 going?

[rodw]

I might be able to help. I'm based on the South side of Brisbane. Basically you have a boat anchor right now. I would propose retrofitting it with Linuxcnc. The Z axis lifter and motor would need to be replaced but it would be doable for a reasonable cost and you will have a very capable table that you could maintain yourself. I have a table at Acacia Ridge you could view.

Feel free to PM me.

[Rick_B]

Before you go retrofitting it out, what's wrong with the yellow box? what is the machine doing? being a school retrofitting is not always the best answer. I had one for a few years and it was temperamental some times.

[racerunner]

Thanks for the replies.

rodw, PM sent.

Rick_B, the machine has a wire going nowhere - as seen in photo, to left of motor. We inquired with a plasmacam rep who told us we needed an ohmic retaining clip but couldn't supply one. The yellow box might be alright. If we can get everything back together there's a chance it will work.

Cheers,
Peter

[rodw]

Thanks for the replies.

rodw, PM sent.

Rick_B, the machine has a wire going nowhere - as seen in photo, to left of motor. We inquired with a plasmacam rep who told us we needed an ohmic retaining clip but couldn't supply one. The yellow box might be alright. If we can get everything back together there's a chance it will work.

Cheers,
Peter

Peter, the ohmic retaining clip is a consumable part available from your plasma manufacturer. Typically they are for machine torches and not for hand held torches.

[rodw]

Oops, did not mean to post so soon!. In the absence of Ohmic sensing, your machine should fall back to stall sensing which I think is how plasmacam does it (or a float switch if fitted).

You might be able to jury rig something up with a hose clamp and a strip of tin. Its worth a try but connecting that wire is not likely to get it going from my understanding of how Plasmacam works.... Unless, they've totally bypassed the sensing circuit.

[Rick_B]

The ohmic sensor is part of the plasmacam hight system and it was used on both machine and hand torches. Mine was a sprung loaded ring on a shaft, I will see if I still have a picture of it. But yer you could use a bit of light metal and a hose clamp to see if the machine goes .
But I would have to say if it goes it's a long way for a boat anchor!

[racerunner]

Thanks you for the tips Rod and Rick.
We will try some things. I'm assuming the strip of tin touches the plate, says "this is zero", and then the head raises a bit to make a gap between plate and torch?
Would appreciate seeing that picture if you can find it Rick.

Cheers,
Peter

[rodw]

Peter, if you look at the photo I posted, you will see the Ohmic clip makes contact with the torch shield. (the brass tip) and the other end would be hooked to that spare wire (via the spade connector) . Another wire is attached to the table/material. The Torch probes down to find the material surface and when the shield touches the material, it acts as a switch and the circuit is closed. The plasma controller registers the material height. It then rises to pierce height, fires the torch and waits for the arc OK signal to be sent from the plasma cutter back to the controller. The controller then waits out the pierce delay and then moves off to cut the job. The arc voltage has a significant peak after piercing and then settles back down to a stable voltage for the rest of the cut. This should be the cut voltage as stated in your cutting charts for your plasma cutter. Normally the controller will enable the torch height control (THC) after a delay to allow the voltage to subside (1.5 seconds is fairly safe). Then if the material warps while cutting, the THC will adjust the height so the voltage is kept stable. There is a very strong linear relationship between torch height and arc voltage so this is a fairly precise method of controlling torch height.

[racerunner]

Thanks for the explanation. I now have a picture of the circuit the ohmic clip is part of.
Then after a bit the THC takes over the height control by monitoring voltage. Nice.
Thanks again.
Peter

[Rick_B]

Peter,

This is all I could find, dont have any good picture of the one that was on my old machine.
This is what come with my machine when I bought it
The one with the ring around it is the one I bought of US ebay when I changed from a hand torch to a machine torch Attachment 446736
I bought the plasmacam back in 2008 and sold it in 2016 is was a good machins. Somedays I wish I still had it, the one I now uses a air ramp to sence the steel and has a 7mt bed but it can can be a REAL prick to use someday.

[racerunner]

Thanks for finding those pics Rick. Much appreciated.