My prefered way is to use adjustable top rails and shims as it's more foregiving and can be better tweaked. It's does take longer much longer than epoxy with lot of time needed to get perfect but when done thats it. Also if the machine frame releases any stresses overtime you can adjust this out if need be which you can't with epoxy.

I'll repeat for the million'th time but build in has much adjustment as possible and brace the hell out the frame and you'll have very very strong machine that's foregiving to those with limited means or engineering abilty. Silyavski as said everything regards welding except spread the heat around and don't weld in one spot for too long. Take breaks and it's a bit like eating an Elephant.? Lots Small bites.! . . . .. This goes thru out the build take it in small bites don't rush just to get it done or the machine will suffer for it.!