lazy susan type bearing? thrust bearing?

[Dick Linn]

In your case, the trailer hub would have to be stationary, just like the upper bearing in your picture. It's probably overkill anyway.

The Magliner hand truck bearings should be 5/8" inside diameter, like most hand truck axles.

In your illustration with the tube, you could use two oil impregnated bronze bearings if you can get a good fit. They are cheap and a flanged type will support the end load. You can get them at McMaster-Carr or MSC.

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=3742

[jspatz1]

The reason the 3-piece thrust bearing in your original post does not have mounting features is that they do not really require mounting. Get one that fits your shaft closely, and it is simply guided by the shaft itself, doesn't need mounting. There is nothing wrong with your original sketch, just need a thrust bearing that fits your shaft. Move the pillowblock bearing up to a high position just under the thrust bearing, as that is where all the side loads will be, and just guide the lower end of the shaft with a loose-fitting bushing.

If you really want a low-profile, lazy-susan type bearing without having a verticle shaft, these ring bearings from McMaster are pretty nice (http://www.mcmaster.com/#catalog/116/1110/=94ojgg), but may be more than you are wanting to spend

[jspatz1]

Originally Posted by sneakyimp

I haven't had much luck finding hubs for shafting over 3/8" -- which is a problem if I use the tapered roller bearing because those are all for 3/4" and higher shafts. Threaded hubs, splines, and keyed shafting are probably not an option because of my inability to machine the shaft or the bearings. Ideally this would use a set screw or clamping mechanism and would have all the holes already drilled in it.

COUPLING SHAFT TO SPEED REDUCER
I've seen shaft couplings and I'm guessing this is what will be needed to couple my shaft to the speed reducer, but they seem so pricey -- $10 at least for such a simple thing. If anyone knows of some alternative, I'd love to hear it. Also, the speed reducer looks to have a shaft diameter of 6mm so we need to couple some larger shaft (10mm? 3/8 inch?) to it.

Here are some aluminum hubs that might be suitable http://www.andymark.biz/hubs.html AndyMark has many hubs, bearings, shafts, collars, and bearing holders that might suit your needs. FRC robot builders rely heavily on AndyMark for parts.

For a cheap shaft coupling, with the low torque you are dealing with, a short piece of stiff rubber tubing and hose clamps might be suitable. The flexibility will allow for a some misalignment in your assembly.

Be careful of "sealed" vs. "shielded" ball bearings. "Sealed" bearings have some friction from the seal and are not free-wheeling. "Shielded" will keep out most dirt and debris, but are low friction. I assume with a wind application you are looking for as low friction as possible.

[Tom Line]

Originally Posted by jspatz1

Here are some aluminum hubs that might be suitable http://www.andymark.biz/hubs.html AndyMark has many hubs, bearings, shafts, collars, and bearing holders that might suit your needs. FRC robot builders rely heavily on AndyMark for parts.

For a cheap shaft coupling, with the low torque you are dealing with, a short piece of stiff rubber tubing and hose clamps might be suitable. The flexibility will allow for a some misalignment in your assembly.

Be careful of "sealed" vs. "shielded" ball bearings. "Sealed" bearings have some friction from the seal and are not free-wheeling. "Shielded" will keep out most dirt and debris, but are low friction. I assume with a wind application you are looking for as low friction as possible.

I was going to point him at the andymark hubs as well.

He can get ground aluminum bar that will fit in them from mcmaster. I would used flanged roller bearings to support the longitudinal loads, with a single thrust bearing at the top to ride on. Picture included.

For the speed reducer I would consider gates belting and pulleys, or 25 chain and andymark sprockets.

In addition, don't we get some dandy pillow-block jounted bearings that are self-aligning from igus that would work perfectly for this that he could bolt to a 2x4? I believe we used ours this year in a prototype shooter design, but if someone has them laying around that might be an easy way to do this too.

Thrust bearing: http://www.mcmaster.com/#thrust-bearings/=94uhvf
Flanged Bearing: http://www.mcmaster.com/#ball-and-ro...arings/=94ujic
1/2" aluminum precision ground shaft: http://www.mcmaster.com/#aluminum/=94uk75

Use andymark hubs. Attach by drilling a hole through the hub and the shaft and pinning (can be done with a drill press so you dont' have to do any broaching for hex shaft or milling for keyways). Andymark has 25 chain sprockets that will bolt up to the hub directly for power transfer.

Use a hole saw to drill holes for the linear bearings then press them in. Put everything on the shaft before screwing in the short 2x4 portions to make sure it's lined up and freely rotating.

[sneakyimp]

J@GMFlint, I tried one of those 6" square lazy susan bearings that I bought at True Value hardware and i really liked the lateral stability and simplicity of it, but It doesn't spin as easily as I'd like and it's far too noisy. Those large-diamter ring-style turntables look pretty interesting.

Dick, I tried finding the sleeve bearings / bushings at my local hardware store and they didn't have any. Home Depot didn't have any bearings at all as far as I could tell so I went to Grainger Industrial supply. Thanks for the link on those bushings/bronze bearings. Those prices look good and I'll probably be buying some here shortly.

I broke down and bought two 2-bolt flange mount ball bearings and a 5" aluminum pulley with 1/2" bore.

jspatz1, thanks so much for the advice about the thrust bearings. I kind of thought they might work that way. The problem I'm having is that only a few of the flange bearings and pillow-block bearings I've seen have an extended inner race -- I worry about the lower thrust washer rubbing on the outer race of my flange/pillow block bearing and causing friction. Of course, it is a thrust bearing? Not really sure how it works. I suppose I'll have to just watch the dimensions carefully.

Thanks for the tip about the andymark hubs. I had seen some on a couple of the robotics sites I stumbled across but the lack of a set screw looks like trouble. I'm not really sure how I would couple these to the shaft. I'm not using keyed shafting or hex shafting.

Thanks for the tip about shielded/sealed bearings and yes I'm looking for very low friction. The bearings I bought at Grainger (which appear to be sealed) seem pretty stiff and the inner diameter is too small to fit the 1/2" steel tube I bought. They were also fairly pricey (@$16) so I think I might take them back and get some flanged bearings (and a thrust bearing!) instead.

The 5" pulley I bought looks like it'll make a nice hub. It's nice and wide and I've drilled 4 holes in it. I'm a bit concerned about the shape of it though as the part containing the set screw is precisely the shape that would scrap against the outer race of a bearing [see attached image].

Truly excellent suggestion about coupling to the speed reducer. I was considering trying to have the shaft machined to 6mm at the end. I'll figure that out once I've costed out the options. Thanks also for bushing suggestion, I'll probably get one of those recommended by Dick.

Tom, thanks for the drawing! And thanks for the suggestions about pulleys and belts. I had originally looked into that and decided that it was going to be difficult to get spin ratios high enough. I probably need 20 or 50 to 1 unless I want my entire song playing several times per second. That's pretty tough with pulleys.

Thanks for being sensitive to my inability to key the hubs and bearings. I'm going to look for some flanged bearings tonite and see what I can find.

I'll also be looking for shafting that will actually fit into the tolerances I get from grainger. Is it safe to assume their 1/2" shafts will fit into their 1/2" bearings or do manufacturers expect customers to machine these parts after purchase?

EDIT: Forgot to attach picture of my hub. Note the set screw bulge and the holes I drilled.

[sneakyimp]

BTW, the Dayton flange mount bearings from Grainger are SO QUIET. I'm kind of excited about using a good bearing. Really hoping for some really quiet, sturdy, low friction results. I'll be using 1/2 inch shafting so I expect it will be pretty sturdy.

[PAR_WIG1350]

You could use epoxy to attatch the shaft to the hub.
Just don't get any anywhere you don't want it. (like on/in bearings/bushings or any part of the shaft that thet passes through these.)

[jspatz1]

Don't worry if the bottom thrust washer contacts the other bearing. It is a bearing, eliminating this friction is its job. (If you are still trying to picture how the thrust bearing works, it is a 3-piece sandwich...washer - rollercage - washer. They are not connected, just aligned together by the shaft.) You should however make sure the bottom thrust washer is relatively well supported, not just by its very inner or very outer edge. If in doubt, add a another plain washer between the bearings.

A tapped setscrew hole is very easily added to any hub or coupling you encounter that needs one. A tap at the hardware store is < $5, and you'll have it for next time. If you need a lesson on tapped holes, we could do that.

[jspatz1]

Originally Posted by sneakyimp

[b] The bearings I bought at Grainger (which appear to be sealed) seem pretty stiff and the inner diameter is too small to fit the 1/2" steel tube I bought.
I'll also be looking for shafting that will actually fit into the tolerances I get from grainger. Is it safe to assume their 1/2" shafts will fit into their 1/2" bearings or do manufacturers expect customers to machine these parts after purchase?

You will find that plain steel or aluminum rod or tubing will not fit in a bearing of the same nominal size, such as "1/2 inch." Bearing bores are made to very close tolerance, and plain rod or tubing is not, and is usually slightly oversize or out-of-round. If you are only inserting the rod into the bearing a short distance, you can sometimes grind or sand down the diameter until it fits. Not pretty. To get a shaft that fits the bearings you will need true "shafting". It is made to close tolerance and is slightly undersize. If you buy stock called "shafting", "machine shafting", "ground shaft" or "precision shaft", it should fit your bearing. Grainger should have some, it will cost more than rod or tubing.

[Tom Line]

Using anything other than precision ground from mcmaster will result in getting bar that is over your required dimension and it will NOT fit (we had this experience the past year). The precision ground is a little more expensive, but will fit perfectively.

On another note, imagine my chagrin to discover that the pages I thought I was linking to linked to only the intro page and not the product I had looked up. Grumble. Do a search at Mcmaster for each one of these.

Ball Bearing:6383K241
Thrust Bearing:6655K17
Precision ground 3 foot 1/2 inch dia. bar: 9062K313

[Dick Linn]

You can get bronze thrust washers which can also be used as spacers ;

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=3743

Drill rod is a cheap source of precision ground stock, though you still have to watch the tolerances. ENCO has drill rod on sale quite often.

[jspatz1]

Despite all this discussion of ball bearings, thrust bearings, and pillow blocks, I would have to say that I agree with Dick's preference for plain bronze bushings for this job. Much cheaper, much simpler, and adequate for the light loads in this application. A simple flanged bronze bushing at the top, maybe an additional bronze washer under the hub, and a bronze sleeve bushing and the bottom. Would last a long time, and could be replaced several times for the cost of bearings and pillow blocks.

Also not mentioned yet....if this is an outdoor application, steel bearings and ground shafting will quickly rust out in the weather. Some stainless shafting through bronze bushings will work well and be fairly weather resistant.

[sneakyimp]

Amazing advice guys. Thanks.

I'm definitely going to try Dick's suggestion with oil-impregnated bronze sleeve and thrust bearings. They are just too cheap not to try and the argument about corrosion is a really compelling one. I also expect they'll be very quiet.

I can also get the flanged ball bearing and a thrust ball bearing for under $10 so it's definitely worth getting those too for comparison.

Dick's also right about enco's drill rods being cheap. They have product #409-0029 which is under $6 for a 3-foot length. Tolerances are +/-.001 so I'm not sure if they would fit with some of the bearings/bushings I linked above. Those tolerances are better than the +/-.002 that McMaster lists for #86705k411 Wear-resistant stainless steel (type 410, $6.50, 12" long) but it'd be nice to order everything from one place to maybe save on shipping. Plus I don't need the full 3' length. Any thoughts on whether I might get away with these tolerances for the bearings I plan to use?

If the shaft tolerances are important, I might forego the stainless steel shafting for the 12" Unhardened Precision Steel Drive Shaft #1346K17 (about $7). OR I might splurge for the 12" Easy-to-Machine Stainless Steel (Type 303) Precision Ground #88915K221 (about $13). The extra $6 is pretty cheap insurance to get something that is
* precision tolerance
* stainless steel
* easily machined

Since I'm using set screws I was wondering if I should maybe use a D-profile shaft (round shaft with one flat side). The have a 12" Type 303 Stainless Steel #8632T87 for $16.40 and a 12" AISI 1045 Steel #8632T7 for $9.27.

jspatz, Thanks for the additional info on the thrust bearing. I know how they work, I'm just a bit concerned about the diameter of the lower thrust washer and the shape and diameter of the races of the flanged ball bearing upon which it rests. I'm guessing it's bad if the lower thrust washer contacts the outer race of the flanged bearing. And what do you mean about a tapped set screw hole? Am I to understand that a local hardware store might drill a threaded hole in some arbitrary hub for $5 so I can put a set screw in it? That would be awesome as then I'd only need to find some hub stock.

It's beginning to look like I can get all my bearings, bushings, shafting, and shaft collars for under $30. I hope to place an order tonight or tomorrow on this. I hope you guys might weigh in on the shafting before I do. Is stainless important? Is drill rod enough or do I need precision shafting? Should I get D-profile or regular shafting?

THANKS so much. I'm getting pumped for this.

[Dick Linn]

Don't worry about a D-shaped shaft. You can easily file or grind a flat spot where it matters.

As far as tolerances on the shaft and bearing, I'd say it's a crap-shoot. Getting pieces-parts from various sources is hit or miss and you may have to do some fitting.

Stainless may be a good idea if you want to leave this thing out in the weather. Do consider some makeshift baffles/seals to keep stuff from blowing onto/into the bearing surfaces.

[jspatz1]

One nice thing about bronze bushings, if your shafting doesn't quite fit, you can easily ream it out with a drill for an working fit.

As Dick said about D-shaft...you only need a setscrew flat in one spot so just grind that in, or drill a small crater with a drill point. Doesn't need to be precise. With bronze bushings, it would be best not to have the edges of a D-shaft turning in your bushings.

On tapping a setscrew hole...what I meant was that you can buy a tap (small cutting tool that turns a drilled hole into a tapped hole) and drill and tap a setscrew hole yourself. Easily done with a drill and vicegrips. Don't let lack of setscrew hole keep you from using a part that is otherwise perfect, you can add it.

Regarding the thrust bearing contacting the race of the flanged bearing...you do NOT want the thrust bearing resting on the inner race of the ball bearing. This would mean that the ball bearing is supporting the weight of the system, and the thrust bearing is doing nothing. The whole point of the thrust bearing is to bear the weight and keep side-load off of the inner race of the bearing. You want the thrust bearing supported by a stationary surface. Add a big washer under it if necessary to make it rest on the outer race or housing.

Yes, drill rod is perfectly good enough if it is cheaper for you. Note the tolerance to be sure it will go in the bearing.

As to whether stainless is necessary, that only depends on the environment it will be in. If it is outside, ground steel will rust pretty quickly. If you really want to avoid the expense of stainless, you can try to wax, oil, or clear-coat the steel shaft, but that will be somewhat temporary. Plated shaft with a rust resistant surface is sometimes available, but I don't recall McMaster having it.