MY 4`x 4` table

**m_c** · 09-09-2008

THC does sound quite simple in theory, but I'm guessing it's more complicated than what it first seems.

Basically you need to know when the plasma is active, so you can then measure the torch voltage (doesn't campbell's use a suitable placed inductor, rather than direct monitoring?), smooth that voltage/signal to remove spikes/dips, then compare that to a reference voltage. Then depending on voltage, either signal the torch to be moved up (increase voltage) or down (decrease voltage).

Sounds quite simple, and I'm sure you could design a crude set-up to move the torch up/down, but getting something on the level of one of the commercial/pro-hobby boards would take quite a bit of work.
Would certainly be an interesting project for someone with the electronics know-how...

**Robin Hewitt** · 09-09-2008

As I understand it...

1: Drop the torch till it touches metal.

2: Back off to pierce height

3: Establish an arc, wait for the pierce

4: Drop down to cut height and start moving X Y

5: After a short movement, measure the volts and save that as the benchmark.

For torch height I used 4mm studding with a 2:1 reduction pulley off a zippy DC motor. There is a chopper disk on the motor shaft for initial position and a digital voltage regulator to control the speed. I plan to measure the torch voltage many times a second then switch the motor speed/direction/brake accordingly. Not much of a plan but it's all I've got :D

**Steve-m** · 09-09-2008

Hi

Well Robin the idea originally was bolt together aluminium 60 x 60 for the bridge, that's what all the holes are for in the plates, I can change at a later date, every thing is only bolted. I rang some one in Yorkshire abut some they said they had it in stock, I drove 150 miles there one way, only to be told sorry they made a mistake, I said ****** ***** **** off! and made it in steel.

I plan on making the table then setting the whole thing up with a dumpy laser level and shims, the bridge bowed when I welded it but only by .02mm, I set it up on the mill put the center bolt in the linear rail and a DTI in the chuck and clocked it parallel then bolted it, I then assembled the Z upright, put the DTI on that and clocked the gear rack 2 ways so that's parallel to the rail. all the slots are for setting up gear racks and reduction belt adjustment, I may pivot the motor and belt plate on springs to "track" the gear rack if I have problems

As for cutting thick material, I mostly want 5-6mm occasionally 10mm, so I have plenty of spare capacity, its not for work only another tool for my "Play pen"

My plasma has all the CNC connections on a plug already, "okay to move" "torch on" "power" and dose not have the HF start, so no damaging spikes, Its real strange it will fire in the air, and with out the earth it will gouge 10mm plate 4mm deep ( I could not work out why it would not cut, DOH!!) I can also touch cut at full power, 60A, running the shroud tip directly on metal, so it is possible to simply rest it on the metal and drag

Unfortunately electronics and I dont get on, Im colour blind and resistors are a nightmare, so I dont do any circuit boards at all, unless its plug and play. I played with a osiloscope, when I did my degree, no matter how hard I tried I could not find ITV and the picture was rubbish all spikes and wavy lines, and it was so small LOL

Steve