BuildingAfloat

[Jonathan]

Opted for 12mm steel for strength ... I thought I'd keep the aluminium down to a minimum for stiffness.

20mm thick aluminium would be just as strong. You will save the difference in price between aluminium and steel from the relative machining difficulty.

I'll see what the 20mm gains me in reduced overhang, it might be worth a drop in stiffness over 25mm. What size do people tend to go for?

I think we're talking on cross purposes - I was referring solely to steel plate, not the rails. However since you've mentioned it - the 25mm rails are much better than 20mm since in addition to being a bit stronger due to the size they also have one more row of ball bearings in the blocks.

I had considered that, may look at the drawing again, I have to mount limit switches yet and thought the space could take the mountings for them, that was all.

Having the machine as strong as you can is far more important than having a convenient place for a limit switch. You'll find somewhere to put them.

1) A simple MDF bed with 2 layers, support and spoilboard
2) Aluminium (or maybe even steel) drilled and tapped
3) Open to allow a 4th axis to be mounted
4) A removable T Slotted Steel bed across the front cross member
5) Open to allow me to mount motorcycle engine casings on the bench beneath for engraving

Although clearly 1) is the weakest it's not a bad idea to use MDF to start with as it will be adequate for most things, makes clamping easier and doesn't kill the tool if you make a mistake.

take a look and see if you can spot the mistakes..lol

[...]

Thats better..

Your dimensioning still doesn't add up. Mine is definitely different to that drawing - size, aluminium piece on front is a different shape, smaller connector.

There's also now 4 bearing spindles readily available - these are 215mm long instead of 200mm.