Don't quote me, but I think you need a gas welder, but you can also use a tig welder. Not sure
http://www.weldingtipsandtricks.com/welding-4130.html
They are welding 4130 chromoly with a tig, but idk. Just google it....
Why would you need an aluminum welder for chromoly pipe? That wouldn't make sense. Anyways, you want it to be Tig welded. Tig welds are cleaner and much stronger. Heliarc machines work good for this. But if your dad is making them and he knows what he is doing, he will know what welder to use.if you have chromoly pipe can you weld it with just a normal welder or do you need an aluminium welder?
TIG WELDING didnt you guys go to metals class?