Dumb post about changing ball bearings.

[Dr. Rob]

I feel kind of dumb. You know, "Oooooh..."

I spend a loy of time chasing down ball bearings of special sizes for special applications. It seems a lot of time is wasted, because I always find ones that are just aaalmost right.

Duuh. I just realized that BB's are not like completely permanent...if you don't like their dimensions, it is no problem at all to turn them down in the lathe or add a flange or a circlip. Or cut a recess for o-rings, or taper them a bit. Make them spherical or self-centering...
Slow turning speed, fine feed, light cut with a carbide tip...piece o' cake.

I hope someone remembers this and makes use of it when the need arises; it will save them some trouble.

[Spin Doctor]

I just hope that you're taking care to get any chips and debris out of the bearing assembly. Radial and tapered roller bearings are not expensive and are usually generally available at any bearing supply house. I definetly would not try this with any precision angular contact or precision tapered roller. It isn't worth the potential cost if screw up. Besides the reason that most bearing sizes are oddball is that they are METRIC

[Forrest Addy]

Hm. It's not that difficult to adjust a bearing diameter. Bearing races are machinable using ceramic tooling and of course you can grind and hone them. You do have to be fanatical about internal cleanliness but that's to be expected.

My question is why? My career has stretched over 40 years in heavy industry and in that time I've only once had to machine a bearing race and that was for a second snap ring groove.

Work your local bearing supplier. It's his job to come up with replacement bearings for you. Fetch him a sample: (Bet you can't match this one.) and he'll be all ofer it with his worn out dial caliper and stacks of catalogs. You may not like the price but you can ALWAYS find a suitable bearing if it was made on Earth.

[Uncle Dunc]

>> You may not like the price ...

The price would have to be pretty d*mn scary to make machining an outer race in a home shop the more attractive choice. You may be better equipped than I am, but I wouldn't care to try it in my home shop.

[Dr. Rob]

Whoa, what did I start? Somehow I made myself unclear... I'm perfectly familiar with the manufacturer's catalogs and commercial availability of unusual sizes. I'm also aware that unusual bearings come from unusual places and are not cheap. ("Well yes sir, we found your 3.14 bearing on Neptune, and it costs 9000 bucks...")

The whole point was that I needn't locate the bearing or go to Neptune or spend the bux, when all I want is a flange on one end. An easy quick-fix, that's all.

In this case it was a machine spindle that needed an axle of a specific size, and needed to be crammed into a housing of a specific size. Solution was to just trim the outer diameter a bit. Spent one day trying to work around the problem, another day locating a NASA bearing, and about twenty minutes just trimming a bearing I already had for free. How's that?

[Spin Doctor]

If you had to reduce the O.D. of the bearing to fit just how much was the reduction? If it was only in the range of .005" to .025" it makes me wonder if the bore was right in the first place. And no one's trying to start any arguments here.

[Spin Doctor]

One other thing, i seriously doubt that any of us really have the machinery capable of achieving the level of concentricity needed in a home shop.

[kap pullen]

I worked for an instrument company some time back.

Every thread we cut was a bastard.
It wasn't a 1.000-32, it was a .980-32 thread.

It was done so you would get frustrated making a spare part, and buy their overpriced replacements.

Wouldn't be surprised if some companys skim bearings off in the grinder for that reason.

Whatever works for you.

kappullen

[Spin Doctor]

This may or may not be amusing. It depends on your out look. For several years I was responsible for repairing and rebuilding the machinery in our tool room and cutter grind departments. Well one days one of the T&D apprentices lunched the front bearing in a smaller K&T universal mill. No problem, diassemble the head, order new bearings & seals, fix any dimensional problems on the arbor,,,right. The front bearing would not move. Tried heat, no go. Finally cut the gage off to get at the race. The look on my bosses face when I showed him that the race for the front bearing was part of the arbor was really priceless. When I called the service department at K&T the first response I got was a chuckle and the service rep told me I'd just joined the club. Seems the only way they could get the proper bearing and the tool holder in the arbor was to go that route. We had to send it in to K&T to get ground and then Timken Would grind a special set of rollers to match the corresponding change in taper angle. And thats the primary reason I think modifying bearing sizes is a dumb idea for the most part. Yes it can be done when required but there are usually other solutions to the problem.

[Dr. Rob]

Well sure Spin, of course it's a dumb idea. I would never, ever dream of putting something like this into a production scenario. Of course not- think of all the frustration and added costs it would induce. And when designing a new component, of course I start with the known parameters of available components. Established standards are paramount.

The point was, that in a tight spot with few viable alternatives, this one presented itself very nicely. It's a machine modification, and I am the one & only owner / user of the machine. No harm there. With regards to accuracy and concentricity, I don't have any better equipment than anyone else, and can achieve only what may be deemed normal for the circumstances. Really it isn't that important, since the bearing (outer, newly machined race) lives in a casting on a fully adjustable slide. It still spins perfectly, and would even if I had so made it into some wierd polygon shape.

So from one Doc to another, man...Sorry if this idea somehow got your stethoscope all knotted up, but it was only intended as a simple D.I.Y.-when-you're-in-a-jam-fix-it trick.

And, if the unforeseen should happen, the bearing is labeled with its original number and diametral reduction. So, no future confusion.