Thanks for the comments - got me thinking again .

The idea of the 4th axis along the side is very interesting. But I don't think I have either the physical space to extend the machine or a design for the Y axis that can pass the X axis linear bearings. So I think I will stick with the current layout and look at the option of possibly removing part of the bed, especially as I had not planned on a 4th axis (but now getting interested).

The ability to machine the edges of boards with a small changes to the design does seem like a good idea. What sort of overhang should I aim for ? I was trying to keep any overhang as small as possible to stop any possibility of ringing.

I have been considering having an adjustable bed, but can't decide if it is better than raising the work piece with a secondary bed.

I think I should start a build log for this design so that I can start asking the questions that are still needing answers. I can then post some more detailed pictures with better perspective and dimensions.

Thanks for the complement JAZZCNC, I hope my research has been along the right tracks (as most of it came from here). As a beginner it is very hard to decide if the available information is relevant to my requirements and if it is also good advice from someone who has real experience. This usually means more googling to see if it makes sense to me.

Thanks again for the encouragement and comments, much appreciated.

G