Quote Originally Posted by routercnc View Post
On the overall design it will work fine, but do think through if the underslung ballscrews will be easy to set up and align. Imagine that the base frame cross members (which the ballscrew blocks mount to) is not perfect, and end up on a different plane to the rails. It will tend to bind the ballscrew at some point and you will have to shim something in the system.
If you go the more traditional route with the ballscrews mounted down the side, driving the side members of the gantry directly (no underslung part), I think all the connections can be made with the appropriate 'slip plane' to get it aligned. This will quicker, cheaper and simpler to build and would be my preference.

Up to you but just make sure you can visualise the adjustment process for any scenario if it is not perfectly built.

If you are going underslung just to stiffen the gantry I'd put the efforts in on the gantry itself, e.g. plating across the back etc. (Not saying it needs further stiffening mind).
Thanks for the advice. The way i imagine it is the screws first need to be on the same plane as the gantry travel. With the current design this can be achieved just with shims. Then the screws need aligning to the axis. Hopefully there will be enough play in the holes in the BK supports to allow enough adjustment. If not i can simply drill over sized holes in the underside of the frame, and use either nuts inside the tube, or if i cant get a spanner in there make a small plate with 4 threaded hole. This will give me plenty of adjustment to compensate for the inevitable poorly assembled frame!