have had another think, about if i can use the same principals used in making a jig for the top, in the overall machine design and i have had an interesting thought and wander what you think. ?

am using 100mm by 5 at 1200mm high, for 4 main legs at the machine corners. with very accurate bolting patterns pre cut. and patterns drilled for threaded bar. For the lengths (x,y), i was looking 2 lenghs per side of oblong profiles, like 80,160,4mm, cut at 2500mm and 1500mm.

And hers is were the idea come when considering plans for getting the frame as dimentinaly perfect as possible with simple tools. and an easy to build jig/vice.

I can build a simple jig for the bolt patterns, small, and very accurate, Lay out the lengths of 80,160. Accuratly place/fix/drill the jig at set intervals don the X and Y lengths. Doiong it like this, i can initialy ignor any twists in the metal, becuase i only need the 200mm long section were the Jig is to be accurate, so the angle of the bolt holes are perfect ( 5 pattern ). Do this for all the cut lenths and supports, accuratly mesureing were you place the jig..

Lay out the first 2 X sides, on top of 2 lenghts of 100mm/4m at 1200, with the accurate bolt patterns in, Put one bolt in each far corner to get your first square-ish, If any of the other bolt patterns line up perfect, fabulas, but not expected at this stage, Take one of you central struts, put a bolt in the top right, and if you can, bottom left, slight movement of the frame should allow this, Then, use the cheep threaded bar, to do you frame adjustments, dropping bolts in as you work outwards, at this stage, most but not all bolt points will fit.

Do this to both X and Y sides, Dont force ANY of the bolts in, only the ones that fit.

Assmble the sides and cross struts with the same principal, each accurate bolt fitted will pull the hole frame into shape, useing simple threaded bar and nuts to ajust. i should be able to get the frame very close to perfect within reason.

I would be relying on accurate mesurments over small areas, not long lenghts.

I also think there are some other good reasons for this,

1. your using shorter lengths of metal, its easer to pick out or cut reletivly straight lengths, and you still only relying on the small areas of 200mm long being dimentonly accurate, any you could probably pick them out by eye and simple tools.
2. You use the smaller lengths to pull/push the longer lengths into perfect shape, adjusting with threaded bar and nuts.
3. It would make the assembly process at lot easer that wielding, and take out any chance of the wield putting a twist in
4. could be done with pillar drill, £ 40 micro-measure from maplins, basic desk top printer.
all the bolts will only fit when it is,

It will cost a bit in bolts, but, can not see many other problems but can see lots of benefits, like stronger machine, more bolt points, simple