Homemade TIG, AC/DC, HF...

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Hello ,I'm from France, so, sorry for my bad english.A (facebook) friend from usa and i are working on a DIY cheapy TIG welder, w/ AC/DC, HF, and maybe pulse.the idea would be this :First design :A motor driving 1 big (150a) alternator, with the rectifier removed, the power cables  to a switch ( sorry i dont know the name of it, even in french, it is like a Railroad switch, 1 input of 2wires , and 2 outputs of 2wire each that you can select.) one of the output straight to the panel for AC Tig (60hz i guess for a car alt) , and the other one to a bridge rectifier and then to the panel for DC Tig.Then to this i add : HF Box, Gas Solenoid, a device to cut the welding current, a footpedal (sewing machine), wired to a 12vdc device to the field of the alt ( to act as a dimmer, btw what range of welding current we can obtain by variing the field voltage ? )Second idea : Same as the first but using a buzzbox as powersource.I have electrical drawings made by my friend, (in english for sure)  110Vac is the power outlet, i guess its 110vac in USA, here in France its 220vac 60hzM is mototA alternatorGas is Gas solenoisRelay is a solenoid that cuts the welding current ( no slope down, i have another idea of using a dimmer to vary the field current down to create a taper slope,  crater fill if im right)Variac in the pedel is a sewing pedel so its a "dimmer"AC-DC selector is the "switch like a Railroad switch" that i was talking about, just like a Synchrowave AC DC selector.at the bottom you can see the torch and work ground wired on ac and dc at the same time, its to illustrate the 2 pluging options AR is the Argon tank.12V is the 12v supply for field, and 12v components such as gas solenoid, hf box, relay...So wacha guys think about the idea ? is that possible or am i lunatic ? some improvements ? any ideas for diy pulse ? and frequency/balance control ?THX Attached Images
Reply:I think your missing the points or spark gap is what they are called, I think.  Somewhere I saw Tungsten tig rods used for points and a brass bearing I think. Also, for some reason, theres always two spark gaps and the gap width is critical. Other than that, I cant offer you any advice on your current design and my mind is all foggy rite now. One more thing; I think an automotive ignition coil has been used somewhere to make homemade HiFrequency for TIG. Good luck and I would like to see your working unit so that I can copy it.One question: what should the range of HiFrequency be?
Reply:I will take my time on this build.when it will be done (if i can do it for real) i will post the plans and part list.for hf i dunno, im a dick at electrical/electronic stuff, lol
Reply:The spark gap is part of a spark gap oscillator (Google it). Basically a cap is charged until the voltage is high enough to bridge the spark gap. It sparks, draining the current from the cap and the process starts over. When the current is drained across the gap, it is dumped through a coil that serves as a primary winding of an air core transformer. The secondary of the transformer is in series with the welding lead, so a high voltage spike is induced in the lead that bridges the gap from the electrode to the work, starting the arc.
Reply:Hi, I have to wonder in this day and age of cheap small hobby welders why anyone would want to go so far to re-invent the wheel, especially starting with an ungoverned petrol/generator current source.Any problems you have with the weld characteristics will no doubt be voiced here for an explanation and a detailed solution.......nobody blames their equipment.......that's a sign of a bad workman.If you can afford to buy in all the bits and pieces without making a mismatch or mistake, you can afford to buy a complete Tig outfit pre-loved.If the object is to have some fun building a Tig outfit, the end result often gets sold off to some beginner who doesn't understand that you only get what you pay for.I believe the going price for a small complete Tig outfit, sans gas bottle etc, is about $1,000 last I saw one, and it comes with a 12 months warranty.Ian.
Reply:This guy made a home made HF unit but he's got three ark gaps instead of two.  Also, notice hes using TIG electrode for spark gaps.http://www.casano.com/projects/hfstart/index.html