[stokestack]

Hi all.

I'm not a mechanical engineer, but occasionally I need to build something.

Currently I want to attach a wheel assembly (truck) to a piece of tubing that rotates in a pillow bearing, so it can spin. So I bought a bearing with a 1-inch inner diameter, and a 1-inch-OD piece of metal tubing. Well, the tubing won't fit into the bearing. I guess that makes sense.

My caliper shows the ID of the bearing to be up to .999" (hard to measure accurately), and the OD of the tube to be 1.003".

Attachment 311902

Do people just grind down the tubing in a situation like this so it fits? I guess this is kind of a silly question, because what else is there to do? The next-smaller size tubing would not sit centered in the bearing, obviously.

I don't have a proper workshop, because I live in an apartment in L.A. Considering that situation, I have a lot of tools I suppose (drill press, table & miter saws, X/Y table). But for something like this, it means manually grinding away metal with sandpaper I guess. Any insight appreciated.

Gavin

[A_Camera]

Hi all.

I'm not a mechanical engineer, but occasionally I need to build something.

Currently I want to attach a wheel assembly (truck) to a piece of tubing that rotates in a pillow bearing, so it can spin. So I bought a bearing with a 1-inch inner diameter, and a 1-inch-OD piece of metal tubing. Well, the tubing won't fit into the bearing. I guess that makes sense.

My caliper shows the ID of the bearing to be up to .999" (hard to measure accurately), and the OD of the tube to be 1.003".

Attachment 311902

Do people just grind down the tubing in a situation like this so it fits? I guess this is kind of a silly question, because what else is there to do? The next-smaller size tubing would not sit centered in the bearing, obviously.

I don't have a proper workshop, because I live in an apartment in L.A. Considering that situation, I have a lot of tools I suppose (drill press, table & miter saws, X/Y table). But for something like this, it means manually grinding away metal with sandpaper I guess. Any insight appreciated.

Gavin

I don't know if this helps, but I'll try.

Have you tried to put a thin layer of some kind of lubricant on the inside of the bearing? That's what I'd try first, because it might be a measurement error when you measured the diameters. Be careful, once the pipe starts to slide in, make sure you don't have to force it too much because once started to force, you might not be able to push it all the way without hammering and you not always want to hammer on bearings. If you use a hammer, try using a rubber mallet or a piece of wood between the bearing and the ordinary mallet. It is important that you only hit the tube of the bearing, not the house.

If the above would not help then the way I'd do it is I would put the pipe in the freezer over night. That would shrink the pipe probably enough so that it would fit. After it is fit, if you leave it in room temperature it would expand again. Tight fit is good and normal, if you grind the pipe you might not get it round enough so it will not fit that well. I don't know what to do if the pipe is too long or you can't put it in a freezer, but another option would be to use a can of freeze spray at the end of the pipe and spray it until it shrinks enough. A third option is to put the end of the pipe in a bucket full of ice.

Heating the bearing would be another option but it might cause damage to the ball bearings or might melt the lube inside, so I would not do that if I could avoid.

Good luck.

Edit: Note that it is the pipe you have to cool down, not the bearing. If you cool down the bearing you will get the opposite effect and will make the inside diameter of the bearing even smaller, so the pipe will definitely not fit. Of course, in that case just wait a few hours and in the meantime, cool down the pipe and redo the process. If you use spray, be aware that you might need quite a large tube and you must use gloves, not spray on your hands because you might get some injuries.

[Wrat]

Do people just grind down the tubing in a situation like this so it fits? I guess this is kind of a silly question, because what else is there to do? The next-smaller size tubing would not sit centered in the bearing, obviously.

Every situation exists, but I've just never seen this one.

That's because mating a heavy-duty pillow block with a lightweight tube is pretty uncommon when compared to say, using a ground shaft.

So, straight off, i'm guessing concentricity and lateral loading is not a big priority. The question is "how far up the tube is this gonna go?" If you're just holding on by the ends (like with another pillow block), this is easy.

Get yourself some sandpaper and do the freezer trick.

Overnight in the coldest freezer you can find. See if it'll go in, even with some pounding. You could warm the bearing, but not with torch. Just slightly too hot to handle. 200F oven. Electric blanket. Something you can hot-soak it in.

Whether you sand it perfectly is beside the point. You're looking for a tight fit between the tube and inner race, is all.

So it goes something like this:

Deep freeze the tube overnight.

Give the bearing a few hours in a heating pad on high or oven on crazy low.

Test fit. Yes/no?

Start stroking the sandpaper. Clean off all the little bits of grinding.

Back to step one. Repeat until it goes in.

Landlord never has to know you've created machinery in your apartment ;-)



Wrat

[ger21]

Pretty much any steel shaft that needs to fit into a bearing needs to be precision ground. If not ground, then chances are the shaft will be oversize, or not even truly round.

Otherwise, due what the previous poster said.

[stokestack]

Thanks for the suggestions, guys. The freezer idea is, of course, sensible. But I'll wait on that until I'm done building the rest of what I'm making before trying it, since I don't think I'll get it back out once it warms up.

The easiest thing to do is show you what I'm making. I built a camera dolly that rolls on PVC pipe with skateboard wheels. After initially making it so the wheels were attached to one rail on each side, I realized that I might want to use curved track someday. So I cut the rails and made four independent trucks that can rotate. At the time, no amount of Web searching turned up the magical term "pillow bearing." So I ended up having to use small lazy-suzan bearings. So far the dolly works great, but now I'm going to make it three-legged (so it can't teeter on uneven surfaces) and I'd like to replace the somewhat flimsy bearings with proper ones for this application. Here is the situation:



As Wrat supposed, lateral loading isn't a big concern. Concentricity is desirable, but we're not talking about high precision here. The tube just needs to be long enough to go through the dolly platform, bearing, and truck. My main concern is how to attach the tube to the truck. There may be quite a bit of weight pressing down on it, but the truck can press against the race of the bearing (if that's the correct term) underneath the dolly; thus slippage of the shaft in the bearing isn't a big worry.

Any suggestions welcome!

Gavin

[awerby]

Why are you using a tube instead of a solid shaft? Given that you may need to remove some of it, the tube may be fatally weakened by the time you get it into that bearing. A solid shaft wouldn't have that problem.

[vegipete]

Since your loads aren't very high, you could perhaps change the 'precision' shaft to a cone and a bolt. The big size of the cone must be bigger than the hole through the bearing. This will center nicely when the bolt pulls it tight against the rest of the structure.

Note also that the bearing you pictured is self aligning. The outside shape of the bearing is spherical and it will rotate, like a ball and socket, in the cast iron pillow block if a sideways load is applied to a shaft (or equivalent) protruding from it. Normally such pillow blocks are used in pairs and the ball shape allows the bearings to align with each other.

[stokestack]

Since your loads aren't very high, you could perhaps change the 'precision' shaft to a cone and a bolt..

Thanks guys. First, I'm using a tube because I have to cut it by hand! And a solid bar would be tremendous overkill. A 1/8"-walled steel tube is more than string enough, especially since the load is applied to it lengthwise and divided among at least three assemblies. In fact, the bearing will support the load; the tube is only to provide the axis of rotation.

So I searched for "cone and bolt" but got a broad variety of results. Is there a particular "cone-and-bolt" assembly I should consider?

And considering what you pointed out, I don't think this is the type of bearing I need. I don't want play that allows the deflection of the shaft to align with another bearing; I just want to use the one bearing and have the shaft spin in a rigid position. Looking at this further, I can probably use a much smaller flange-mounted bearing and just dispense with the tube altogether in favor of a bolt. Something like this. Thoughts?

[G59]

My caliper shows the ID of the bearing to be up to .999" (hard to measure accurately), and the OD of the tube to be 1.003".

Firstly, you will never be able to shrink a total of 4 thousands of an inch by just cooling the pipe down(unless you cryogenically freeze it). Not on a 1" diameter overall. Secondly, overnight in the freezer, is exagerated. 1 to 2 hours is good enough for steel pipe. Even less for Aluminum.
Sand the end that the bearing will mate to (remove any burrs and reduce the diameter of the shaft to within 1 or two thou), depending on how tight of a fit you want. Once you are ready to assemble, push or press the bearing on in 1 stroke. Any misalignement and you will have to hammer or pull the bearing off.
Good luck.

[vegipete]

The alternate bearing you found: Attachment 312494 is also a self aligning bearing, just using a 2 part (2 mounting hole) stamped shell instead of the cast iron piece of the previous version. (If you look closely at the zoomed version of this image from the original site, you can see that the bearing is slightly twisted in the housing - which is quite normal.)

If you went with a 1/2 inch or 5/8 inch bore flange bearing, then a 3/8 inch flat head bolt would provide the 'cone and bolt' all in one:
Attachment 312498Attachment 312500
My junk happened to include a 1/2 inch bore 2 bolt flange mount bearing so this shows what it would look like. The max diameter of the this particular bolt head is a tiny bit under 3/4 inch.

The self aligning feature could be very useful to get the truck spacing to match the track, and even compensate for irregularities. The stamped steel housing could be extra useful because some creative tweaking could lock two bearings so they don't swivel, and allow the third to move to follow the track around left and right bends and straights.

[john-100]

Hi Gavin

for inspiration , have you looked at how camera dollies like this from Vinten are made ?

Vinten | tracking dolly | tracking dollywww.vinten.com

each rail has a conical socket on one end and a conical pin on the other end
so the joints between two pieces of track are always aligned

Attachment 312504


John

PS

here is a DIY dolly

DIY Track Dolly for under $50

[stokestack]

Thanks for digging up those pictures, guys!

To join track lengths, I use short bars of 1" PVC pipe. They fit almost perfectly inside 1 1/4" pipe. I wrap a bit of packing tape around the middle to make them snug. Very nice because for $25 I can add another 10 feet of track at any Home Depot. I have been pondering how to use metal conduit in situations that require more rigidity, and for that I would indeed need conical joiners of some kind.

I have seen dollies like that. Mine is heavier duty, more than sturdy enough for me to ride along with the camera. I also have large solid-wheel casters on the other side, so I can flip the dolly over and use it without track if the floor is perfectly smooth. I plan to keep this level of construction, but probably go with a T arrangement to simplify its design and allow me to break it down for transport in a bag. Unless I'm overlooking something, Pete, I don't think it would be necessary to lock any of the bearings in place to follow a curved track.

I considered whether the "self-aligning" bearings would be helpful for this application, but I don't want them splaying outward when weight is applied, or allowing the platform to shimmy from side to side (although they're probably too tight for this to be a real issue).

So my question is: What flange-mounted bearings do NOT have this sort of deflectable bore? I haven't been able to figure out what the magic word is in product descriptions. Is it "pillow" that describes this action? How can I ensure that the bearing is one that rigidly holds the shaft perpendicular to the mounting plate?

[plasmamatt]

Is it pipe or tubing that you are using? Pipe is rarely round and would present this type of problem. DOM tubing is very accurate and should fit into a bearing of like size. Cold rolled solid round is also very accurate and should fit Generally a 1" bearing is slightly larger than the specified size. The steel dimensional tolerance should go under and not over. I would also cut a little bit off the end if you haven't done so already. Often times the end of the bar stock is not as accurate. I would also chamfer the end a bit to make it easier to install in the bearing. I install DOM and CR shaft in bearings all the time without the need of grinding.

[rockcliff]

Yes, tubing is probably not the best choice for bearing shaft, unless it's absolutely needed, you can easily purchase ground shafting, or sometimes it's called superior shafting, from most metal distributors, or as mentioned, DOM

0.003" is not much, normally for this amount of oversize, we would use a lathe, to file, or use some sandpaper to bring it down to size. just remember because it's seamed pipe, it can be out of true, and might wobble a bit, even if it fit's the bearing.


As for bearings, most flange or pillow block bearings have a spherical for alignment, so you always need to mount them in pairs, to have stability on the shaft

[stokestack]

Thanks, guys. It's not pipe. It's steel tubing from onlinemetals.com. It is DOM:

1" OD x 0.065" Wall Mild Steel A513 Type 5 DOM Tube - 12"

If I had a lathe, it would be a lot easier to sand it down to size.

Anyway, the question I can't seem to get answered is: What is the name of a flange-mounted bearing that will hold the shaft perpendicular to the bearing base (and mounting surface)? If "pillow block" means NON-rigid (self-adjusting, to be used in pairs), what is the term that means rigid (which doesn't need to be used in pairs)? How can I determine, from a product name, whether the bearing is rigid or not?

I have posted this question in forums, and I've asked bearing vendors... but no one has answered.

[rockcliff]

Thanks, guys. It's not pipe. It's steel tubing from onlinemetals.com. It is DOM:

1" OD x 0.065" Wall Mild Steel A513 Type 5 DOM Tube - 12"

If I had a lathe, it would be a lot easier to sand it down to size.

Anyway, the question I can't seem to get answered is: What is the name of a flange-mounted bearing that will hold the shaft perpendicular to the bearing base (and mounting surface)? If "pillow block" means NON-rigid (self-adjusting, to be used in pairs), what is the term that means rigid (which doesn't need to be used in pairs)? How can I determine, from a product name, whether the bearing is rigid or not?

I have posted this question in forums, and I've asked bearing vendors... but no one has answered.

fixed, supported, are some of the terms used for what I " think " your looking for, they normally have two opposing taper bearings inside the housing, and are generally much more expensive, sometimes you can get better answers if you actually post a picture of a rough sketch of what your overall design is going to look like,

Pillow block, flange is only the mounting, both can be found in fixed or self adjusting

[stokestack]

Thanks. I did post a couple of pictures on the first page, and the new design is simply to replace the lazy-suzan bearing that attaches those trucks to the dolly platform with a more robust bearing. I can just run a half-inch bolt through a bearing and the truck and the platform, if I can acquire the right kind of bearing.

[rockcliff]

Normally what I would do, is use 2 of the self aligning flange bearings you have shown in your photo, mount them back to back, (one on the top side, and one under the plate) and you will have a fixed bearing that won't swivel

[stokestack]

Yeah, was considering that, but was hoping to minimize bulk, weight, and expense by just getting a rigid one.