Well here goes... Aluminium frame router design

[JAZZCNC]

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.!

[CharlieRam]

I'll repeat for the million'th time but build in has much adjustment as possible

This is why I revisited the frame but what about the rail mounting surface, would it be accurate enough to skim the top face on a milling machine and bolt the rails directly to this or do you still recommend the epoxy and if I go the epoxy route would I be able to seal all the threaded holes by covering the screws in molten wax or will the epoxy melt the wax while setting?
Just to say, I am a competent machinist and I'm quite confident in my skills, it is the welding that I will struggle with but I'm sure it will come good!
Cheers, Charlie

[JAZZCNC]

Yes skimming surface will be fine and all that's needed. Then just shim the rails onto same plane if needed.

Welding at this level is simple just practice on some scrap and you'll be fine. Where not welding oil rigs here so bit of pigeon shit is fine and it all cleans up with a grinder.