Quote Originally Posted by Jonathan View Post
If you do add one it needn't be thick - 10mm would be fine as it's only to stop the joint between the plates that the Y and Z bearing blocks mount on bending.
Know this is a bit late 3 weeks after posting but I've been asked for some input by Adil and was looking over the build again and spotted this comment.!!

Jonathan never have understood why you use this rear plate in the way you do because that rear plate on the back add's very little protection against the joint between Y axis bearing plate and Z axis rear plate bending in the vertical.?
The only forces that apply here are vertical force applied from one side and the overhang distance from the Y axis bearing plate to Z axis rear plate is nothing.? possibly few MM's. So the chances of that joint bending are zilch and if the forces were great enough to bend that then the rest of the frame and gantry are in big trouble and 99% sure something else would be bending/breaking much sooner.
Your design is an open ended box with very little strength in the vertical direction and if enough vertical force is applied at one side the other side will deflect in a similar manner.!

If you want to brace for that movement then plates on the side bolted into both plates would be much better and could be much thinner and still give far better bracing support than those backplates.? This back plate just add's weight and cost IMO for not enough gain and isn't required.!