First time build - Steel Frame CNC Router

[Clive S]

Thanks guys, to confirm, it's just the green bits in the last post its being used for (2x bed supports and some braces).
Only place it needs to be tapped is on the bed supports, so that I can bolt down the ply wood bed onto there. Any options for this with the 3mm box section? Maybe drill through and use a nut/bolt setup?

You don't say what size bolts you want to use. If you drill through the box without a spacer in the box you have the chance of squashing the box of course you could use self tappers.