Rotating Ballnut - design ideas

[JAZZCNC]

Reading this thread with interest (as I may need to go this route on my "big" machine soon), I noticed the concerns over rotation speed of ballnuts. This made me recall some stuff I read in the TBI catalogue some months back about different types of ballnut (differing mostly in the configuration of the return paths) and their relative speed capabilities, worth a read and maybe doing the sums they outline there.

Certainly worth a read but what helps with rotating nut is to get shortest length Nut possible.
It's also critical that the Shaft as a Flange which is machined perfectly concentric to the Nut otherwise concentricity to the screw is misaligned so causes big vibrations.

[Voicecoil]

Certainly worth a read but what helps with rotating nut is to get shortest length Nut possible.
It's also critical that the Shaft as a Flange which is machined perfectly concentric to the Nut otherwise concentricity to the screw is misaligned so causes big vibrations.

What's the thinking behind the shortest possible nut please?

The concentricity is an obvious thing and might rule out some of the cheaper offerings if my experience on the machine I've just completed is anything to go by. Having set everything up and got it working smoothly I thought I'd spin one ballnut through 180deg to get better access to the lube nipple. Major fail, that side of the axis got really stiff, it turned out that the casing/flange of the ballnut was something like 1 or 2 degrees out of alignment with the axis of the screw.

[JAZZCNC]

What's the thinking behind the shortest possible nut please?

access/interference and balance/inertia mostly, it's no big deal and depends on the design to some degree but shorter is better in my experience.

The concentricity is an obvious thing and might rule out some of the cheaper offerings if my experience on the machine I've just completed is anything to go by. Having set everything up and got it working smoothly I thought I'd spin one ball-nut through 180deg to get better access to the lube nipple. Major fail, that side of the axis got really stiff, it turned out that the casing/flange of the ball-nut was something like 1 or 2 degrees out of alignment with the axis of the screw.

It's not always the case obvious to everyone that's why I mentioned it. However most ball-nuts, even the cheap ones, have a machined reference surface on the outer body which you can chuck upon and skim flange if needed. Thou I've not had any issues if honest.