taper roller bearings vs deep groove ball bearings

[dsc]

Well to start with this is all vertical, so anything hanging off the ball bearings will be adding to the overall axial load. In normal running conditions the axial load is low, so I had a 'bright idea' moment today and came up with this:



ie. single circlip and a bolt from the top which attaches the shaft to the top bearing, the low one is simply for support and to add more stiffness. Great right? wrong. I think the shaft hanging off a single ball bearing (shaft is SS, weighs a few kg), the additional axial load from running the thing and simply any play in the bearing will most certainly not give me zero axial play.

I like the idea of preloading, as it fixes some problems, but looking at the above you can see that adding two lock nuts to the top will be problematic as well. Normally a preload is applied by tightening one lock nut and locking two nuts against each other. I will have no access from the sides so that operation will be tricky or at least no-so-hassle free. Second thing is that tapper roller bearings need to be lubricated (me thinks) and I'd much rather have a sealed unit which simply runs without touching it.

DTI is not an issue, heck I have a prototype with tapper roller bearings which has zero axial play, but I'd rather avoid the problems described above (the prototype doesn't have a whole in the upper horizontal plate and so is easy to preload with lock nuts, although the bearings are exposed). Angular contact bearings might be the answer, but single rows will need preloading (ie. lock nut issue) and double rows will not work that great as I need bearing support 100mm apart.

To answer your questions:

1) Arrangement is back to back, like here, but with 100mm between the bearings:

http://www.skf.com/binary/21-3541/1_...cm_12-3541.gif

2) I'd say warm up/expansion is not an issue really, there will be a puller between the bearings, but most 'cutting' will be done 150mm below the bottom bearing.

3) Speed: 200-300RPM

4) No lubrication

Thanks for your help m_c!

Regards,
dsc.