Accurate Strong Gantry

[vargai]

Looks good but you might need a bit more triangulation. The thin gussets only work in one direction so ideally you need them in equal amounts in all 3 planes.

Why is there a bit gap in the middle?

What rails are you using? There are different types and some can handle 4 way loading and others cant so are best mounted on top of the rail. Especially if you are using a heavy moving gantry.

Yes some corrective action should be done .

The gap in the middle just represents the place of the single ball screw in case of narrower machine

regarding the rail I would use one like this which is regular type now
The problem is as you pointed to it at my case only the upper row of ball hold the load but the moment resistance is good that occurs at start-stop and direction change
I have no experience using it but suppose it works -the catalogue also mention it as possible mounting arrangement

Because of my 100kg+ heavy moving gantry I have drooped this design and go with fix gantry where the moving Z will be balanced

[Boyan Silyavski]

The Hiwin HGR are double row bearing blocks and there is no difference how you mount them, so don't worry about that.

For a router HGR20 is enough and even a bit overkill, depending on the design. So no worry here also.

[Ross77]

Ok, I'm a bit confused. You keep saying fixed gantry but then you show a bed with rails on the side.

Is this the bit that will be moving? If so I would have said that it is not the best way to do it. Moving beds should have the rails underneath and at approx. third points or a quater in.

That way the rails are supporting the load better and are closer together so you can get away with one ballscrew.

As you have drawn it the bed can bend in the middle under load.