Game on!

[Voicecoil]

After some lurking, quite a few questions, a lot of sums and some FEA I've just started building my first machine. It's not as big as I really need (I want to cut out large loudspeaker cabinets amongst other things), but I'm having a lot more difficulty finding larger premises than I thought I would. So having kind of got the bug and wanting to get on and do something I thought I'd make a small (but capable) one anyway, the experience will do me good, it will be useful for machining up metal parts and a lot of it will be transferable to the big machine design when I get the space.
Sorry I've not shared any of the initial drawings, but I don't really do 3D CAD and without being able to turn layers on and off and have the thing in your head, the 2D drawings are a bit of a nightmare to interpret. The design ethos is:
1) To try to keep all individual deflections of the gantry extrusion/side beams/bed to less than 1um for a 50N cutting force - this has been determined by calculation (thanks @routercnc for the spreadsheet) + FEA
2) Minimise twisting moments by keeping all assemblies as compact as possible - no massive spindle overhang please!
3) Keep the number of bolted joints to a minimum.
4) Try to get a good price performance compromise
It's being made out of aluminium extrusions/plate simply because I'm able to machine that better and more accurately - and you can anodise it to a nice finish

Not having any CNC machining capability until it's made, I'm having to "bootstrap" the process, apart from one or two pieces that I need to get laser cut, it will all be done using the trusty Elektra Beckum chop saw, a drill press (Axminster ED16B2) and my little lathe. First job was to fettle up the saw and make a decent clamp for it:

With a new blade fitted and a few minutes true-ing it up it goes through 15mm plate like a knife through butter. Squareness is about 0.25mm across a 125mm cut, and with a wee drop of WD40 to help the cutting, the cut ends are smooth as a b******s bottom.
First parts to make were the carriage plates for the Y axis (please note I denote X & Y from the point of view looking down at the front of the machine i.e. the X-Axis runs L to R along the gantry):
here's marking them out using the trusty optical centre punch: