[Robin Hewitt]

I'm just remaking my bench sized mill a bit, want to get it right this time.

I have a notion that the best way to hold a ball screw is under tension between two axial bearings. The most compact way to get that tension is with Belleville washers.

From somehere in my dim and distant past I also have a notion that 560 lbs of tension is about right, a quarter ton. Does that sound credible or am I way off the mark?

To gauge the tension I'm thinking 2 washers with different rates facing each other. One crushes flat at around 560lbf and acts as the gauge, the other is altogether stiffer and still has some way to go.

Bellevilles don't exactly appreciate being crushed flat so guess I'd have to replace the lighter one whenever I wanted to recalibrate.

[LeeWay]

I personally don't think bellvilles are needed in a drive bearing setup. Thrust washers are more important. You can use a pair of those, one on each side of a standard good quality bearing and apply preload with the nut. You can locktite the nut or back it up with a locknut to hold the assembly.
I did something similar on my lathe and got great results. Bellvilles just aren't needed for this.

[Robin Hewitt]

I personally don't think bellvilles are needed in a drive bearing setup. Thrust washers are more important.

What is a Belleville if not a thrust washer?

I started without any intentional spring in the system then added a die spring PDQ.

Now I'm remaking it (with the benefits of CNC and hindsight) I want to make it pretty and do all the things I didn't realise I needed last time around. Things like double ball nuts, more iron, less aluminium etc. Also I won't restrict the X,Y movement when I can so easily extend it. I have even remembered a conduit attachment point on the X.

Bellevilles it must be, only thing is choosing the right Bellevilles

[RICHARD ZASTROW]

Robin, Have you also considered wavesprings? www.smalley.com

Just something else to add to the confusion. lol

Dick Z

[Robin Hewitt]

Just something else to add to the confusion. lol

and I'm quite easy to confuse I'll give you that

Isn't the wavespring designed to put a long spring in to a short space? I rather liked the enormous rate to be had from a Belleville for this application.

The price is good to.