Hi Andy,

Your machine is starting to look really good. A suggestion (from a non-plasma expert!) is to consider running a simple bearing from the back of the Z axis plate onto the top and bottom of the upper 40mm rail. This would give a bit more support to reduce the sag, and possibly help with the resonance (if that is due to the round unsupported rails vibration). Just a thought . . .

In terms of running the x axis rails on top, rather than on the sides, I've always wondered if this was easier from a build point of view. As drawn the gantry has to be very precisely made so that it is a nice fit onto the rails. The rails or gantry might need to be shimmed to achieve this. If you put the rails on top then everything can be bolted together and settled before finally marking the holes into the frame. Maybe there is another way but this seems a bit easier to me.

Good luck with it,
Barry