Aluminium Profile Type Router - Initial questions

[JAZZCNC]

On the dual plate, to be honest I did think of it earlier on, but at the time I was going in circles with the design and if I could physically make it so opted for a simple single plate. Jazz - I see what you are saying, essentially the ballscrew is fixed square with the frame, but the gantry may need slight squaring.

Yes and no.
What you are doing when squaring the gantry is setting it perpendicular to the MASTER RAIL and NOT the frame. Infact forget the frame because unless you have built it perfectly square and aligned the Master rail perfectly parallel to it then you CANNOT measure from it. The MASTER rail is the ONLY reference point you work from.

So the ball-screw must also be perfectly parallel to the MASTER rail. Likewise, the Ball-NUT is set parallel to the gantry side.

So if you have set your ball-screws perfectly parallel to the MASTER rail, which you should have done. Then any angular adjustment on the gantry in respect to the MASTER rail means there must be an angular twist between the Ball-NUT and Ball-SCREW and this will cause excess wear and binding.

The goal is to get the gantry perpendicular in respect to the MASTER RAIL and the ball-SCREW perfectly parallel to the MASTER rail. This will then put the Ball-NUT perfectly parallel to the ball-SCREW.

When all this is done then this will show you how much Shimming and spacing is needed at various places around the machine in relation to the Frame. If you have built a perfectly square frame then it should be easy.!!

You may find the best place to shim to get square without impacting the screws/nut relationship too much is between the Gantry plates and profile at each side.
This is where building in lots of adjustment points comes into play and helps with setup and fine tuning, don't be surprised if this takes you many weeks to get right with lots of strip downs.

Edit: I've just done a quick sketch in SW to show how much just 1deg of misalignment translates across the length of a gantry or machine.
The measurement show the numbers except one and that is the twist of the ballnut in relation to the ball screw but the number is 0.70mm of twist which would wear a ballnut out in no time and cause lots of binding.

I'm hoping I can get slight adjustment if I have to go there, from shimming either ballnut or the gantry side/ballnut fixing. I have built in a very slight tolerance by using a 1mm thick piece of rubber between gantry side and ballnut fixing, which can compress 0.5mm ish to accomodate a slight twist.

The Rubber is BAD idea, your basicly building in Back-Lash. The rubber will allow it to float even under compression. Don't underestimate the forces and the amount of inertia that will be applied to ballnut which transfers to the ballscrew which pushes on the Endbearings which will be sat basicly on rubber engine mounts.!!

Jazz - looking forward to your machine unveiling, maybe I can swap it with mine..

Oh don't be getting too excited I've not re-invented the wheel and the design is nothing special or new. It will just be built properly and strong compared to all the Cheap offerings on Ebay etc.