taper roller bearings vs deep groove ball bearings

Gents,

I roughly know what the differences are and that taper rollers are better for combined axial and radial loads, at least according to this:

Roller bearings

but I'm wondering whether there's a difference between the two at low loads? I've got a shaft mounted on two taper roller bearings, which will be subjected mostly to radial load (rough torque at around 10Nm) and I'm contemplating using ball bearings, simply for ease of use. With taper rollers you need preloading with lock nuts and oil seals as the bearing is in two pieces. Ball bearings can be preloaded with the aid of springs and are pre-sealed, so no worries about crap getting inside.

Any info on the above is greatly appreciated.

Regards,
dsc.

Provided you are within specs for whatever bearings you plan on using, there isn't much difference.

Double Row Angular Contact Bearing ZZ 3200 5200 Series | eBay

these are worth a look at, they come already preloaded so are a nice easy reliable way into the advantages of angular contact bearings without all the head aches of implimenting the preload

Hmmm, looking at the specs for ball bearings I can say it will work, but...as usual there's a but. The shaft goes through two ball bearings, one in the middle, one on the end. I was thinking resting the middle bearing on a circlip and locking the end one with a cap via a bolt. The main idea is to have zero axial play on the shaft, so the dimensions of the shaft and the space between the bearings need to be spot on, super precise, otherwise I get play or I preload the bearings, neither of which is good. Anyone knows of any ideas on how to solve this?

Taper rollers don't have this problem as you need preload anyway, which then takes care of any axial play.

Regards,
dsc.

There are various ways it could be done.
Proper way would be to shim, but can be problematic getting shims the correct size/thickness.
You say the end one will be held on via bolt. Could you use this bolt to adjust the preload? A bit suitable loctite will stop it from slackening (you could add lock wire or a locking tab for extra security)

Yes, shims, it's been suggested, although problematic as you say. I could make the shaft slightly shorter and then use the bolt and 'cap' to tighten the top bearing, but aren't ball bearings suppose to run with no preload?

As for tapper roller bearings, I've found out that I would need around 3.3Nm of torque for correctly preloading the bearings and this will get rid of the zero-shaft-play problem.

Regards,
dsc.

Ideally yes, but you're not running them in an ideal application.
To set this up how you want, you'll need to use a DTI (Dial Gauge) set-up to measure the end float, then you would gradually tighten the bolt until no end float is measureable.

Would it not be simpler to use double row angular contact bearings as mark mentioned?
That way the preload is preset, however it does mean you need someway to secure the outer into a housing.

Taper roller bearing preload depends on lots of factors. Are they mounted facing or back to back, what part is likely to warm up/expand the most, is expansion an issue, how fast are they turning, what's lubricating them...

What exactly is the application?
(feel free to PM if you don't want to say publically)

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:

Attachment 7993

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.

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I don't know the deep groove ball bearings.