Need 6' x 4' bed, 4 axis router design.. Help..!

[routercnc]

We're deviating from Steve's original topic, but you need to compare like with like diameters. If you start with a solid 16mm dia ballscrew, and compare it to a 16mm dia hollow ballscrew (theoretical) with say a 10mm dia bore, you will find it has less inertia. The reduction is only small because you are taking it away from the middle, where it has less effect.

In your equation R is fixed at 16mm and r varies from 0 to 10mm (in this example). So R^4 - r^4 gets smaller, and the inertia goes down.

[Jonathan]

In your equation R is fixed at 16mm and r varies from 0 to 10mm (in this example). So R^4 - r^4 gets smaller, and the inertia goes down.

Yes, of course. I was tying to compare like with like stiffness not diameter since I was assuming you'd use a bigger screw to compensate.