Unless you plan to butt weld your stainless steel exhaust pipe tube without achieving full penetration (on a 1.5mm wall thickness), you need to back purge the tube ie drive out the oxygen / air from the inside. Failure to do so will result in a shitty black oxide eruption from the back side of the weld. It's called "sugaring" and is best avoided, if only for cosmetic reasons.
The usual requirement is for some form of simple bung to wedge into the end of one of the tubes with an argon supply. Any other openings are covered, usually with aluminium foil, allowing some means for the purged air and argon to escape.
I have dual argon regulators and 2 hoses, so I should be able to adjust the flow of the torch and purge gases independently. It's a little bit crowded / messy up front here but I'm trying to run both gasses through the solenoid of the welder so that I can't accidentally leave the purge running - or forget to turn it on.
The bottle has a sort of master flow regulator feeding the welder, so I'm hoping to be able to set the total flow rate above the sum of the individual flows and/or use the master regulator to achieve the required balance. Time will tell if that is a workable concept in practice. The individual gauges have simple needle valves, whereas the master regulator actually regulates the flow at a constant level, up a maximum (but modest) back pressure. You can see how that might work....
So tonight's challenge is to make a simple tapered bung (in black ABS again, certainly for the moment) that will accept one of those male plugs. They are 6mm and 8mm - and given that I have 2 of the 6mm, I will use that.
This should work for both 32mm and 38mm tubes. The 6mm plug should be a nice push fit into the 5.5mm hole.
Corners rounded off:
That one can join the (growing) queue to be printed.
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