Thank you for your comments and insights.

I agree that a long Y rather than a long X would be more rigid, it is also more expensive (extra rack). I will have another play with it and try swapping it round again and re-cost. Should be cheaper than last time, now that I have dropped profile sides for the Y in favour of Unistrut.

Yes, the Z axis is ambitious, and I have similar concerns, but needs to be if I have any hope of doing anything in the rotational axes, I am also hoping that the X axis is stiff enough to prevent too much flex with the distance between the bearings, it does however have over 400mm of Z travel.

The design is also adjustable in that the bed can be moved up and down manually - probably taking a couple of hours so I can start with it high up and minimal Z travel and then drop it down as I become more ambitious and work out any flex issues.

I also realise that the weakest stress/flex points for my B and C axes will be the joint between the axle and the turntable.

An A/B axis attached to the bed of the machine would obviously be more rigid than attempting to tack it on the end of the Z axis (I have designs for this as well, just not drawn up, although my more rectangular trunion design along with a tail stock would work equally well here).

A spindle would also be less moving mass and torque than a router but I have the router and it was a fraction of the cost of a spindle and VFD.

I am also designing a smaller one for PCB and other small more precision stuff, about A4 size bed, I will post up a thread for this one as well, I am looking to fabricate a spindle for this one from a model aeroplane motor and an ER collet chuck, not looking to do heavy cuts so hoping this will be up to the job (not expensive and easy to upgrade/modify if it is not), Proxxon spindle would be the next choice if this idea fails.

Zebethyal