Quote Originally Posted by brman View Post
Maybe that should have been the question? How best to make a steel frame that is accurate enough?
Tack weld opposite points. Progress slowly and methodically, setting up as accurately as you can and measuring as you go. All you need is a stick welder, a grinder, and a tape measure.

Then level with epoxy. It's completely doable, loads of people on here have written about their experiences and how to do it. If you screw it up (like I did my first time) chip it off and try again.

Alternatively, skip the hard stuff and use aluminium profile. You'll be bolting your rails on in minutes rather than days or weeks (or you know, in my case, months).