Being kind of tired of electrode sticking when trying to scratch-arc-start, how about adding say 5-20 Ohm wirewound high-wattage (nichrome) resistor in series with either electrode, to get tungsten hot and arc start and then shorting the resistor ?
Assuming working voltage of 40V, 20Ohm would limit current to 2A - which should be enough to get tungsten hot w/o sticking and initiate the arc and this is where you'd release the foot swith and eleminate in-series resistance ...
SPST momentary switch rated for high amperage ?