Router mk1 - First dip into CNC

[Jonathan]

is 50x50x5mm aluminium box strong enough or should i be using a solid alu billet for the riser off the linear rails?

I'd go for something stronger.

I don't like ballscrews running along side of rails on flat horizontal surface because they become chip traps. With screws on side chips fall away

If moving the ballscrew doesn't comprimise the strength of the axis, then I agree you should try to avoid letting chips collect on them. However, as I mentioned in this build log, it's very easy to just put 15mm rubber shaft seals either side of the ballnut and they'll take care of the chips.