Z-axis design - help sizing materials please!

[Jonathan]

Luckily the microwave survived - some pretty impressive flames though!

So do you think the price of those rails implies that they are probably not up to much?

16mm supported rail and bearings works out at £93.60+VAT from Zapp compared with £45+VAT for the 20mm unsupported.

The open bearing pillow blocks are only a few £ more, so that's fine. I hadn't thought of stress in the rails. If it does work I reckon it's worth the effort to save about £40!

I'm currently dimensioning the drawing - I'll post it as soon as I'm done. But basically the 4 bearings are currently spaced as a square, 100mm between centres - hence the rails are also 100mm apart. The rails are 600mm long (the above prices are for 700mm just to be safe) which leaves a nice 400mm or so travel.
Thanks for the help so far - much appreciated!

[Robin Hewitt]

The rails are 600mm long (the above prices are for 700mm just to be safe) which leaves a nice 400mm or so travel.

Do you really need 40cm travel? If you have some specific task in mind that needs it, do it, if not you are seriously weakening the machine for no good reason.

If you are not stuck with 40cm, why not bring the gantry down a foot, then increase the separation on the pillow blocks so you can centre support the rail?