Hi George,

Another popular option is to put the motor at the back, as you have done, but at the top driven by a similar belt arrangement. In moment terms, since the weight acts straight down, this is the same as you have drawn and still gives a 'balanced gantry'.

This avoids the problems mentioned by Irving, and still keeps the C of G further back than it would otherwise be, which might be kinder to your side rail bearings, depending on where they are.

I chose this arrangement for my mk2 router, see my post 'time for mk2 upgrade'.

You might also want to consider swapping the Z axis bearings and rails around, with the bearing fixed and the rails on the moving bit, so that there is always a bearing at the lower part of the stroke, giving better support. What you have drawn is the idea that I think most people have at first, and is fine, but the other way has some advantages. Again you can see this idea on my post. By the way, I take no credit for this idea - I read about it somewhere and have borrowed it!