you can use a mig welder without gas but you need flux core wire. thats what i used on my linclon 175 until i got my miller 251. the difference is that in mig welding the IM (inert gas) is a sheilding gas and in flux core you dont use gas so there is no sheilding gas, so the flux core wire has flux in the middle of the wire the acts as a sheilding gas. in the begining it was hard to use the flux core wire on my 175 but after alittle practice I could use it like any other mig welder with gas. the welds dont look as good and is spits alot but they are definatley strong. the whole front frame rails of my truck are welded in using flux core welding. just my 2 cents.