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darryl
02-18-2005, 12:03 AM
I have two pieces of aluminum that need to rotate relative to one another. Not a full rotation, and no speed involved. The catch is that this assemblage can't take up much height, or I could use some kind of ready made thrust bearing.
If I were to turn a groove in each piece and fill that with steel balls, assembling it pancake style, I'd have what I need, except that aluminum is going to dimple from the balls. My option is to use an insert that is a more suitable material, and secure that into a groove in the aluminum pieces. This will all be under some pre-load, so I don't see a problem keeping the inserts in place. I could either cut some rings out of steel pipe and machine the ball race in them, or use some other type material to form the ring shape out of, like maybe 3/16 square key stock. There would be a gap in a ring made this way, but for this I don't think it will matter. An estimated maximum rpm this thing would turn at, if it were to be rotating, which it isn't, is about 30 rpm.
There's very little room for this, but if I use 1/8 inch balls, lots of them, and the rings aren't more than 3/16 high, I could make it fit. This assembly will have an estimated 100 lbs of static load on it, with impact loads probably triple that. The load will be offset, so one side of the race will be taking the bulk of the load, as will one side of the opposing race which is part of the sandwich structure.
I am kind of partial to parting off these rings from steel pipe, since I have it on hand, but if there's a better material to use to start with, then I would do that. I'm mostly concerned with the balls hammering dents in the material if it stays in one position for any length of time, which it probably will. Each race would hold about 75 balls, so there will be a considerable bearing surface in contact between races, hopefully enough to let me use mild steel for these parts. This assembly will basically be a caster, and as far as I can tell, castors are stamped from ordinary steel and they do take the punishment. One thing I thought of using is music wire, silver steel, or drill rod. If that material was available in square cross section, I could use it. Anybody got a lightbulb going off in their head?

precisionworks
02-18-2005, 12:25 AM
Darryl, thrust bearings & matching races are available at all the large bearing supply houses. The races are availabel in "heavy load" (thicker) & "light load" (thinner). These races are hardened & ground, and you could easily machine a wide groove for the races to seat in. The thrust bearing matches the race, and is avialabe in different load capacities to match your application. With this setup, you could reduce your part-to-part clearance to almost zero.

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Barry Milton

Dr. Rob
02-18-2005, 01:27 AM
Yeah, and needle bearings (series AXK IIRC) are even flatter than balls. The races (series AS washers really)provided are only 1 mm thick even at diameters of 80 mm or more. They're also really inexpensive.

Not sure what diameter you had in mind. (Low profile = thin wise, right?)

Randy
02-18-2005, 01:31 AM
Take a look at needle thrust bearings & hardened washers. Cheap, easy to use, high loads and small stack heights are possible.

Evan
02-18-2005, 01:46 AM
Babbitt

precisionworks
02-18-2005, 02:32 AM
Babbitt -- ??? Perhaps you meant Rabbitt!

Sort of like rebate, debate, I'm late, don't wait.

radish1us
02-18-2005, 04:38 AM
Go get hold of a buggered battery operated drill and pull it apart. There is a needle thrust bearing fitted in most of these drills, this bearing is about 3 or 4mm thick and about 15 mm across with a hole in it about 8mm. Now that I have said that, you most likely will have to pull a couple apart to get hold of one of these bearings.

bikepete
02-18-2005, 07:52 AM
How freely do they have to rotate? If that's not critical, might consider just a disk of slippery plastic between them. Or even better, sandwich a disk of stainless between two disks of plastic.

Techtchr
02-18-2005, 08:10 AM
i purchased some very thin thrust bearings for my CNC project from McMaster Carr. Very inexpensive.
Matt

Herb Helbig
02-18-2005, 04:30 PM
darryl -

The latest Rockler woodworkig and hardware catalog showed up today. On page 41 they list a slimline lazy suzan bearing 12 5/8" diameter, 220 pound load, 1/16" thick, black plastic with metal rollers, $10.59.

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Tom CPM10V
02-18-2005, 11:21 PM
Modern needle thrust bearings are stunningly: thin, accurate, inexpensive, capable of high loads and speeds.

wierdscience
02-18-2005, 11:42 PM
Needle thrust bearings all the way,amazingly cheap and carry a hellacious load.

darryl
02-19-2005, 12:43 AM
thanks for the responses. I will definitely look into those needle thrust bearings. I actually have some I've forgotten about, but none 3 inches diameter. This sucker has to handle a fair amount of radial load also, but it's likely I could handle that with a bushing, even plastic, just to keep the parts in alignmemt. If I can keep the plates no further apart than a quarter inch, I'll be laughing. The main requirement, besides fitting in the available space, is to be able to handle a constant static load, but be very free to turn with no stiction. A needle thrust bearing will do that. Thanks.

zl1byz
02-19-2005, 01:12 AM
Hmm, is it a secret what your building. There are a lot of other considerations other than load & speed when it comes to a bearing type. Like providing lubrication & preventing ingress of dirt etc. If these points are not taken care of then any steel thrust bearing is not going to last long. Personally if is open to the enviroment I would use a oil impregnated plastic machined up to suit. But don't know what your doing so could be way off track.

John.