Initial thoughts on new build

[EddyCurrent]

Neale,

I used 50x50x3 for my frame, I knew from the outset this was a bit thin for tapped holes required to mount the profile rails. My intention is to mount (epoxy glue probably) a piece of 6mm flat strap into the upper box section so that my threaded holes will then be 9mm deep.

I don't see any triangulation on your frame looking at the end view.

Chai will machine the ball screws to your specification, I asked him to extend the plain area at the end in order to mount a pulley with the shaft going right through, as you say it was cheaper and easier to get these from Chai already machined. I also could not see that he sold profile rail so I bought it in the UK because it was quick and easy. I used 20mm and 15mm as you mention but I believe 15mm would have been okay all round.