Wobblycogs CNC Mk2

[JAZZCNC]

P.S. I was thinking the gantry back plate would have to stay because the screw is mounted to it but now I think about it I could mount the screw on one of the gantry beams. I'm tempted to still lock the two beams together vertically but with a small plate in the middle of the span. I'll have to have a think about the cover idea as I'm not clear how it would work (I think I've seen what you're talking about in another thread though).

No you misunderstand here I think.? The plate on the Rear of the moving Y/Z axis carriage I meant. It does very little in adding strength, think of box with no sides.!!
Often this way causes more hassle than it's worth because if the edges are not machined perfectly 90deg then when tightened it twists the assembly on the bearings and locks up solid.!!

The slotted front way works great, you've probably seen I have design that uses it so know it works fine but it does cost more. It does offer some nice advantages thou like ball-screws are protected and every thing is neatly out the way. The way I do it the motor and belt are all inside the Gantry and covered up.

The other design which would suit your machine nice and is cheap and easy to build is the L shape gantry using 45x90. I've made few machines with this design and it's proven design which is very strong and reliable. Has some of the same benefits the Slotted design does in that the screw and motor is placed behind the Gantry out of the way. It does put the screw back a bit further than is considered ideal but again It's proven to be no issue in real world use.
If this design interests you then tomorrow I will have hopefully put the final touches to a gantry I'm building so can show the real thing with cable chain, Z axis covers etc instead of 3D model.