thrust bearings

Sounds like a job for opposed angled roller bearings:

--Winston

Normal ball bearing pillow block bearings can carry thrust loads. If the thrust is less than 20% of the dynamic load rating of the bearing you probably don't have to worry. If it's more than that you should go thru the procedure in the bearing mfr's catalog to calculate the equivalent load using your anticipated radial and thrust loads.

You can get tapered roller bearing pillow blocks, but they're larger and much more expensive.

When applying thrust loads to a pillow block you do need to consider the strength of the housing, its mounting, and the means for transferring the thrust between the shaft and bearing.

How much load, radial and thrust, are we talking about?

On Wed, 13 Jan 2010 18:42:34 -0800 (PST), the infamous mark scrawled the following:

Is this loading perpendicular to the shaft? If so, the standard ball bearings in the pillow blocks should handle it easily, if loads are within their normal range.

Non-perpendicular loads would require different bearings, maybe tapered rollers like a wheel bearing setup.

-- What helps luck is a habit of watching for opportunities, of having a patient, but restless mind, of sacrificing one's ease or vanity, of uniting a love of detail to foresight, and of passing through hard times bravely and cheerfully. -- Charles Victor Cherbuliez

s Victor Cherbuliez

I am building an airboat, the prop shaft will be above the engine driven by belts. I was planning on using a 2' long 1.5" shaft supported by 2 1.5" pillow block bearings and then making a hub to mount the prop to on the end of the shaft. The side load of the bearings would come from the prop pushing the shaft. I priced the tapered roller pillow block bearings and they are $350.00 each, not an option. The other idea I thought of was using a 1 piece rear axleshaft from a pick-up as the prop shaft. Make an adapter for the prop to hubface and the tapered rollerbearing on the other side should take the load. Mount the shaft with 2 pillow block bearings. The boat will weigh about 1500lbs and we are using a stock chev 350 at 2500-3000rpm max.

I did some checking and it seems the HC208-24 bearing that these pillow blocks use have a dynamic C load rating of 30000 (N) and a static Co load rating of 20000 (N). What does this mean?

C is the load that 90% of the bearings in a sample will support for 1 million revolutions before failure. Life and load are linked by an inverse 3rd power relation. In other words, if you reduce the load by half, the life will increase 8 times. (2x2x2=8)

Co is the load that will permanently deform the bearing some very small amount. I don't remember the amount off the top of my head.

I for one (and I'm assuming many others here in RCM), would really like to see some pictures of the project.

Thrust bearings can be bought as an assembly, but I've never had a need to find any in the sizes you're needing, so I can't recommend a source. A bearing distributor should be able to help with some recommendations, check your yellow pages to see if there are bearing distributors in your area.

Applied Industrial Technologies is a nationwide USA vendor, which I go to locally.

So if they will handle 6700 lbs of force each then 20% of that as somone above mentioned is acceptable for side load come in at at 2600 lbs side load. That should be fine and I could install a 3rd one for extra strength.

OK so you will have way more thrust load than pillow blocks normally see, but maybe comparable to truck cornering forces, so I like the idea of adapting an axleshaft. But, cornering forces are only intermittent. So I think it might be worth doing some simple design sums. Do you have a prop in mind; if so, presumably you can find out the thrust force at typical revs? Even if you don't have bearing catalogues to hand, post the load and speed here, and someone will help you size your thrust bearing for a given service life.

les Victor Cherbuliez

Take a look at the W.W. Grainger catalog. Not because it has the best selection of bearings. But because they only stock tapered roller bearings that in common use. And the bearings in common use are less expensive. You might note that they stock 1.375 inch bore, and 1.750 inch bore , but no 1.5 inch bore roller bearings.

Dan

I threw out the 20% figure as a quick and dirty place to start. It's more complicated than that and, now that I see this project involves large objects swinging at high speeds near your head , I'd urge you to go thru the bearing manufacturer's procedure to calculate the equivalent load for a combined axial and radial load. Once you have the equivalent load you can figure the bearing's predicted life.

Do *not* assume that the axial load will be shared by the bearings. Do the calculations assuming that one bearing will carry all the thrust.

I now have a new idea. Same as above but I will turn down the end of the shaft (opposite end that the prop is on) from 1.5 to 1.125 and just a bit less than the thickness of a shielded integrated steel ball thrust bearing (mcmaster part # 60715K16) rated at 7000 lbs thrust load. This will be pushing on part of the framework and I was thinking of "bedding the end of the bearing with JB weld or something similar so it will be evenly seated.