So without further adieu... I present the finished DIY Plasma Cutter!!
The torch tip was a eBay special I picked up a few years back when I saw the auction ending and couldn't resist the $15+5 shipping for it! It was a foolish bet, but it paid off!
I have since upgraded it to a ESAB unit. A PT-31 (now using the long tips) to be exact, and I highly suggest you don't skimp here if at all possible. It's worth a few extra bucks for the accuracy of the cuts and quality of the handle!
The indicators on the cover have never been finished (maybe after the cars done) but it's operation is so simple they are not really necessary!
The tip is the heart of this beast and tends to generate the most issues besides the supply voltages.. let me cover both...
I ran the HV Arc Start line inside the protective sheath, into the handle and simply drilled a little hole on top to exit. It then wraps around the head to where I have it zip tied in place. I wrapped it around a piece of SS TIG filler wire which I bent around the tip. This works AWESOME! The only thing to watch for is shorting out the HV Arc Start. You'll notice that it's UNDER the head? Because when it's on the side and you use a piece of steel as a guide, it shorts out and you can't start the cut! Yeah... took me a little wile to figure out just WTF was going on there! After I moved it under the head (simply rotated it) I haven't had any more issues!
BE AWARE: if you are playing with it and do not give the HV anywhere to ground to... it will bite your butt! Ask me how I know! That is why it's in the sheath and doesn't exit till the very top!!
OK, Power Supply concerns..... VERY VALID CONCERN... but simple to dispel.
Yes... I left out the isolation transformer. I have played with and built Tesla Coils (1.5 million Volts - 34" arcs) so I am fully prepared for voltage concerns. Leaving out the iso didn't worry me. I was intending on putting it in, but I found something odd. It makes sense now... but only after you see it happening.
I have actually touched the work... while cutting... without any ill effect. Do I suggest you do this... NO WAY.. not without an isolation transformer... but it got me thinking and looking at just what was going on.
You are converting AC to DC with the Bridge Rectifiers, right? In full wave, there is no direct path to the mains if all the components are working.. Electronics 101. I have measured the frequency of the work clamp (positive) in reference to earth ground.. I get 0 Hz. I have measured the tip (negative) to ground.. yep 0 Hz.. there is no measurable AC voltage at any point past the Rectifier. DC doesn't jump and needs a very conductive path (sweaty wet hands...) to move.
I have touched the clamp to earth ground.. NADA! The tip, unless arcing, is internally isolated by the design of the head, but when disassembled.. it won't short to ground either! Does this mean it's safe to lick the ends... I would advise against it. My rule of thumb here has been to treat it as I treat a arc welder. Yes.. the tips are live and can zap you, but won't unless you do something abnormal.
It's your decision as to how you build it.. do I suggest you forgo a portion of the safety in this circuit.. NOPE! Can it work and be acceptably safe without it.. I believe so.. but you make your own choice!
Well, that's it for my lecture... I present this to you in the spirit of LOCOST!!! If you do build one.. be safe and smart about it. I kid you not.. the caps can store several kilo-joules worth of energy.. plenty to blow a hand off without even fully discharging! And they will self generate... recharge themselves without anything attached to them!!! BE SMART AND BE SAFE!!! If you don't know HV equipment.. find a friend that does before you start! I can't stress that enough!!
Any questions or help required to figure something out.. Just let me know! Happy to help!