Quote Originally Posted by CraftyGeek View Post
I had previously been planning on using steel box - I think we exchanged messages about it ages ago.
I like the convenience that ally profile offers - I also have concerns about getting a frame built with steel box square...although since looking at the supported rails I did think it could be easier to attach them to a frame made from box rather than profile.
What makes you think you'll get it any squarer using Profile than steel.? To be honest it's actually harder to get and keep square than steel.!
With steel (presuming your welding) it's just case of tack it up knock square then when happy finish up the welds while keeping eye on it moving. After that it will never move again.
With profile your messing around with corner diagonal braces and shims etc then first time you move it or shaking thing about a bit while cutting it's moved again.!!!

Like Birchy says with steel it's strong and doesn't need to be micron square. The rails are what matter and steels much more workable than profile so more flexible regards alignment etc.

By the time you have bought the profile and all the T-nuts etc which can cost has much has the profile you'll be into £200 plus with steel you'll do it for £60-80 and still have some left. That's £150 towards your rails.!!!

Meant to ask this before.? What you doing regards screws etc . . Your not thinking threaded rod are you like lots of DIY rail folks do.?
If so then again don't waste your time and go straight for balls screws and get them at same time has rails to keep costs down £300-£350, can get you a set of rails and screws with all end fixings and machining. Wouldn't or Don't even consider Lead screw has again it's not worth the small difference ballscrews cost.
You'll have a proper machine that can do some serous work all day long and will be worth at least double the cost you put into it if done right.

Steel is the way to go IMO Esp if your on budget. Profile looks bling but that's about the only thing it's got over steel all the rest that matters it's behind on.!!