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  #1  
Old 05-22-2010
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Basic machinery questions ...

I'm trying to understand some basic machinery and parts that are sold at a nearby store and I need a little help from you smart people.

1) The store sells bearings, they are round on the outside, on the inside, and come in little plastic packages. Some of the bearings also have a second piece with them that is black and looks like it has some kind of an allen bolt on it, but I have no idea what that part is for, it looks like it may fit on one side of the bearing ? No idea. So that's the first question, what is that part for, maybe it is some kind of seal, or used for lubrication ? Don't know. It is a ring and is smaller than the bearing itself, about halfway between the inside diameter and outside diameter of the bearing.

1a) Using bearings, I don't understand how the bearing "attaches" to whatever axle or shaft is going through it ? It isn't keyed in any way, just a smooth surface, maybe it doesn't matter whether the axle slips on the metal or the bearing turns so long as there is low friction ?

2) The store also sells something called a pillow block housing. Now what this looks like is something you put bearings into so that you can attach them to things, but it isn't obvious how the bearing stays in them, do you just hammer the bearing in ? (Hitting the outside ring of course).

2a) These pillow block housings have a grease fitting on them and a channel around the inside where grease can go, but it looks like if you just hammered a bearing in there the grease fitting would be completely useless, how would it lubricate a sealed bearing ?

2b) Is there an easy/standard way to seal the bearings in a pillow box housing so that they don't get dirt in them ? It looks like if the bearing just fits into the pillow box housing that for the most part it is completely exposed with no cover over it.

3) The store also sells something it calls a hub, essentially a ring that you can fit sprockets and/or pulley wheels to. Those hubs are keyed, and they don't seem to fit any standard sizes of pipe, so I am guessing that there is some kind of an axle or special pipe that you buy that those hubs fit on. If that is the case, do they come in standard sizes, and where do you get them ?

3a) This isn't so much a question, but related to the above, if you have one of these axles and you put a hub on it, the hub as an allen bolt type of screw on it that appears to be for tightening it down on the axle, am I right in assuming that the key is held in between the hub and the axle by the pressure created by tightening this bolt so that they key doesn't slip while the axle is turning ?

3b) How do the sprockets and pulley wheels attach to the hubs ? They seem to spin freely. Do you just tack weld them on ?

3c) The sprockets have two numbers on them, the first I don't know what it is, the second appears to be the number of teeth on the sprocket. Is it safe to assume that the first number is a chain size ?

In general I am also interested in knowing if there are any standard sizes of all of these components that are readily available pretty much anywhere on earth, especially the axle and chains, it did seem like most of the hubs were designed to fit just a few axle sizes.

Thank you for any information.
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Old 05-22-2010
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Okay, what are you building, a go kart or a minibike?
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Quote:
Originally Posted by bljones View Post
Okay, what are you building, a go kart or a minibike?
Well, it is a good guess, but what I am really trying to do is to spin a shaft or axle with a 12vdc motor for no specific purpose at all. It'll be used as a bench tool to drive various belt driven contraptions, possibly thread the pipe or axle to use it as a lathe, etc.

What I want to end up with is an axle supported by two bearings with some of these hubs on it and various sizes of pulley wheels and/or sprockets depending on what I am doing at the time.

I would like to use something like these pillow box housings the store has to mount the axle bearings to a surface.
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Old 05-22-2010
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Get a pillow block with the bearing installed.



McMaster-Carr
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Sprocket info:

McMaster-Carr

Mcmaster-Carr's site is great for this stuff.
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Originally Posted by bljones View Post
Mcmaster-Carr's site is great for this stuff.
Thanks for the link, yes, that is the same kind of things that the store has, I am just trying to understand how it all works (see original post).

I think I figured out part of it. It looks like the axles come in kind of standard sizes and you just get the one that is the right size of the hubs and for the bearings and they all fit together. The hubs are keyed, and from the reading I was doing I get the feeling that what you do is take your round axle to a machine shop with the hub and tell them where on the axle you want to put the hub and the machine shop will then machine the shaft so that you can fit a key into it and then tighten the allen bolts down to seize the hub on to the axle. That answers one of my questions at least.
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exactly. Shafts are standard diameter, cut to the length you want, get a keyway machined in the shaft, slide the shaft through the corresponding pillow blocks, install a sprocket and key, and you are good to go.
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exactly. Shafts are standard diameter, cut to the length you want, get a keyway machined in the shaft, slide the shaft through the corresponding pillow blocks, install a sprocket and key, and you are good to go.
Great, I think I can handle that.

Thanks for the help!
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Wow,
If I tell you all this stuff I'm going to have get tenure, and free health insurance for life!

The bearings in pillow blocks have spherical outer housings. The pillow block housing is spherical on the inside to match. There are two grooves on the sides of the housing that let you puch the bearing in when it is oriented at 90 degrees, then you twist it to the normal position and it can no longer come out. The inside of the housing has a groove running around it. The bearing has a small hole for grease that lines up with the groove. So grease pumped into the housing goes around the groove until it finds the hole into the bearing.

There are many ways to hold bearing on shafts. Set screws,taper-lock bushing, split collars, etc.

Hubs come in all kinds, some are in fact welded to the sprockets or gears, some are keyed, and have snap ring.

Shafting is not pipe, and solid round rod is not shafting either. Bearings are very precisely made. The shaft needs to be exactly the right size to fit properly. So they sell shafting which is ground to exact size, typically a very samm amount undersize so it slides right in. The tiniest burr and it gets stuck, so putting machinery together requires a bit of skill and patience.

Spend some time in the McMaster Carr catalog on their website and you'll have a much better idea of all this.

I take cash, checks, and Visa, keep those questions coming!

Gary H. Lucas
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Wow,
If I tell you all this stuff I'm going to have get tenure, and free health insurance for life!
Ha! Now you've done it, you've shown you know the answers so I won't stop asking questions now!

Don't know about tenure, but the Democrats just gave you health insurance, haven't you heard ?

Quote:
The bearings in pillow blocks have spherical outer housings. The pillow block housing is spherical on the inside to match. There are two grooves on the sides of the housing that let you puch the bearing in when it is oriented at 90 degrees, then you twist it to the normal position and it can no longer come out.
Okay, that makes sense, I did see on the pillow block housing that it had slots on either side, I had no idea what that was and imagined that they were to help remove the bearings if they went bad, like you needed some kind of a tool or something. I understand what you are saying, when I was running my fingers along the inside of the housing I did notice that it was sort of spherical and I imagined that the bearing would be damaged if I just hammered it in, and then it would be loose inside, which made no sense to me. I also wondered why some of the bearings were rounded on the outside instead of being flat across the width.

What you said also makes sense in another way, if the bearings are spherical on the outside and the housing is spherical on the inside then maybe there is a little bit of freedom for it to adjust itself in the housing so that the housing doesn't have to be lined up exactly 100% perfect. It would be hard to get that housing exactly right with the large bolt sizes involved.

Quote:
The inside of the housing has a groove running around it. The bearing has a small hole for grease that lines up with the groove. So grease pumped into the housing goes around the groove until it finds the hole into the bearing.
I didn't notice any holes in any of the bearings, but I wasn't looking for them. I did see where some of the bearings were called sealed, and some I think were called "pre-lube" ?? or something like that ?

Quote:
There are many ways to hold bearing on shafts. Set screws,taper-lock bushing, split collars, etc.
The bearings seemed to all be smooth on the inside.

Quote:
Hubs come in all kinds, some are in fact welded to the sprockets or gears, some are keyed, and have snap ring.

Shafting is not pipe, and solid round rod is not shafting either. Bearings are very precisely made. The shaft needs to be exactly the right size to fit properly. So they sell shafting which is ground to exact size, typically a very samm amount undersize so it slides right in. The tiniest burr and it gets stuck, so putting machinery together requires a bit of skill and patience.

Spend some time in the McMaster Carr catalog on their website and you'll have a much better idea of all this.

I take cash, checks, and Visa, keep those questions coming!

Gary H. Lucas
Thanks Gary for all the great information, that really helps a lot!
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