[QUOTE=grumpygrady;...how about showing how you did the welder[/QUOTE]
OOPS! Untill all this time later, I didn't reqalize there were more posts and a question.
The welder is neanderthal technology, but it is extremely reliable and consistent. A battery powered hankscraft motor rotated a wood disk with a copper contact plate attached to it, The plate has notches cut out of it at random widths and spacing.
The pogo pin (little spring loaded plunger) brings `12 volt power from a transformer on to the plate. The 2 wipers pick it up. One wiper goes to one light bulb. the other goes to 2. That way the intensity of the flash varies, anywhere from none, one, 2 or 3 bulbs flashing at rapid random appearing intervals.
This is always hidden behind the subject being welded on for obvious reasons.
An AM radio tuned to no station is placed next to this mechanism and picks up static from it, resulting in a nice zapping welding sound. All this stuff is in the diorama's control box, and is connected to the dio by wires about 2-3 feet long. The speaker is removed from the radio and placed in the bathroom of the dio, with the door sligfhtly open, so the noise comes from in the shop.
Control box. Contains the welder unit, light circuits, fan circuit, and an FM radio that is also piped into the "bathroom" so the sound is in the shop. I don't have a picture of it open showing everything inside at once.
Radios
Attaches to the bottom of the shop floor thru a DIP connector (custom made computer plug, parts avail at radio shack)
Sorry I was so late in replying to this question. I recon there are better hi tech ways to accomplish this effect, but this was easy for me to build 13 years ago, and it has been reliable. It sure goes over well at shows! Dan