Potts milling spindle max rpm

Hi everybody,

some months ago, after a long search, I purchased on Ebay a Potts milling spindle; I was wondering about the maximum rpm it can handle safely (bronze or brass plain bearings).

On the web there are formulae to compute this, but perhaps somebody in the forum knows the exact value.

Many thanks,

Massimo

I would imagine that there are too many factors involved for anyone to give a difinitive maximum RPM.

A few I can think of include, rubbing materials, lubricant, clearance. surface finish, axial/radial loads, ambient temperature, quality of construction.

You are probably best running it at increasingly higher speeds whilst monitoring its temperature. as long as it does not cook the lubricant you should be OK. Its a similar process to finding the correct torque settings for important bolts (tighten them until they shear and back off half a turn!)

Ian P

Massimo,

For comparison, the Cowells lathe headstock is similar in size to the Potts milling spindle. Cowells give a maximum speed for their lathe with a soft steel spindle in cast iron bearings as 2100 rpm and for a hardened steel spindle in bronze bearings as 4000 rpm. The Arrand ball bearing milling spindle has a stated maximum speed of 8000 rpm. I think 3000 rpm would be as fast as I would want to go with a Potts.

Hope all this helps,

Rod

An intresting question Massimo,

I made a Potts from castings (I think the main body was the legendary meteoric iron fantasy heroes get their swords forged from). There was no mention of service speeds.

Like Rod I would imagine it is not suitable for speeds abovea couple of thousand RPM, and would suggest a ball raced spindle with adjustable preload for high speeds.

Apparently the Workshop Practice Series 'Spindles' book by Harprit Sandhu has some good designs in it.

Neil

Ian, Rod and Neil, thanks for your replies.

My spindle seems to have been built from a kit, so the spindle shouldn't have been hardened; I think I'll keep around the speeds you suggested and take a great care of lubrication, As the spindle will be used for fairly quick jobs, it should have a rather long life expectancy.

Cheers,

Massimo

If its from the same kit as mine, I think the spindle material is a medium carbon steel, it should last a lifetime at reasonable speeds and model engineer levels of use.

Neil