1/2" ID ball bearing interference fit

[DaveD44]

I'm machining the axles for my 7.5" gauge locomotive tender trucks and I'm using ball bearings mounted outside of the wheels in journal boxes. These ball bearings are USA made by Nice and have an nominal ID of .500, supposedly varying from .4995 to .5000. (I'll try to get some accurate ID measurements of some of the eight bearings, but haven't done so yet.) I want an interference fit of axle to bearing ID and I may supplement the fit with an anaerobic shaft retainer when I do final assembly, but in the meantime I need to disassemble/reassemble the axles and bearings from time to time during construction. The bearing to axle fit must be fairly tight since this connection will provide part of the truck dimensioning stability in operation. So I have a couple questions:

1. What would be the best fit in terms of axle OD to bearing ID to make it fairly easy to disassemble/reassemble yet remain solidly pressed on and unmoving in operation?
2. I will need to press these bearings that are designed for an radial load, but the inner race will be behind the larger diameter of the axle. I understand these bearings can take an axial load up to 30% or so of the designed radial load of 1850 lbs. dynamic. Can I safely press the bearings off the axles with pressure on the outer part?

Thanks guys. Great forum here!

[Doozer]

Think electric motors.
The ball bearings are press fit on the rotor shaft
and the races are a slip fit in the motor end bells.
I am sure if you look at the literature available from
NICE that they tell you a press fit, but for a .500"
shaft, I would go with a .0002" to .0004" press fit.
The standard of .0005" to .001" press fit per inch
of diameter is a good rule. So .0004" would be
on the tight side and .0002" would be on the loose
side. These numbers are not too easy to hit.
Keep in mind, that surface finish is related to size.
With press fits, even more extremely so.
If you have a coarse finish and do your measuring
and you think you have everything right, just
remember that you are measuring the peaks of
the surface. Once you press on the bearing and
press it off again, you will have knocked the peaks
down into the valleys, and it will measure smaller.
Most electric motor manufactures cylindrical grind
their bearing seats on their rotor shafts. And for
good reason. I figure most home shop guys will
turn it oversize on the lathe and then polish the
shaft to side with emery cloth. It hurts me pride
to do this. So I have purchased some good
lathes and even a few cylindrical grinders. That
makes it easy with a cylindrical grinder. It actually
makes it fun. A lot of fun running a cylindrical
grinder and being able to take a tenth of a thou.
I even bought an ID grinder because it titillates
me so. But anyhow, your ideals might be different.

--Doozer

[Toolguy]

Lots of good information, Dooz. Additionally, do NOT press the bearing on or off a shaft by pressing the outer race. That will damage the bearing. Maybe you could make your axles with a threaded hex nut part on the back side of the bearing to press them off by unscrewing the nut?

[eKretz]

I would agree with Doozer except that you wrote "frequent assembly and disassembly." I would not recommend that. Try to work around that so you don't need to do it or your fit will gradually loosen. Assembly is best done with a little heat. Warm up the bearing to ~200°-220° F and it will slip right on by hand. (Wear gloves). As previously noted, do NOT push or pull on the outer race while the inner race is held by a press fit (nor vice versa) - unless you plan on tossing out the bearing and replacing it.

If you absolutely must retain the ability to frequently disassemble and reassemble the axle and bearings for fitup purposes, since this is so small I would recommend making a quick mockup axle with slightly smaller journal diameters so the bearing can be easily slipped off and on. Then when everything is all done, use the axle with an interference fit at assembly. For that size bearing, I agree with Doozer that .0002"-.0004" interference should be plenty. I'd shoot for the lower end if you're capable.

[SVS]

Would an extended race bearing with eccentric lock collar fit your plan?

[MikeL46]

If you really need to take it apart several times, you might want to sacrifice a bearing set. Grind the ID oversize for a slip fit. For final assembly use the real bearings.

[Rich Carlstedt]

Keep it simple--if you want to assemble/disassemble multiple times, just make it to size -.0002" (ie) and then use
Loctite bearing retainer when doing final assembly of your R8 bearing.

Rich

[Tim Clarke]

I'd consider making a set of dummy bearings for easy disassembly, and use the ball bearings at final assembly

[Doozer]

If you harden the shaft to Rc 35-40 then it can take many pressings on
and pressings off. Or you can buy half-hard 4140. Even 1144 is Rc30
to Rc34. If it is bugger soft 1018, you are not going to enjoy the experience.
And Loctite in my mind is a good engineering solution. Just don't let it wick
into the bearing. Ask me how I know. It will even enter a rubber sealed
bearing. Baaahhh ! ! !

-Doozer

[Sparky_NY]

If you harden the shaft to Rc 35-40 then it can take many pressings on
and pressings off. Or you can buy half-hard 4140. Even 1144 is Rc30
to Rc34. If it is bugger soft 1018, you are not going to enjoy the experience.
And Loctite in my mind is a good engineering solution. Just don't let it wick
into the bearing. Ask me how I know. It will even enter a rubber sealed
bearing. Baaahhh ! ! !

-Doozer

All great advise you are giving ! You can tell its not your first Rodeo.

[oxford]

And Loctite in my mind is a good engineering solution. Just don't let it wick
into the bearing. Ask me how I know. It will even enter a rubber sealed
bearing. Baaahhh ! ! !

-Doozer

I’ve done that before.

[Mcgyver]

IF you do use loctite, use the right stuff.....the low strength one that gives it up with a bit of heat. I forget the number, but fail to heed that and there's a chance the parts won;t survive disassembly. Personally I favour the bearing co's recommended interference fits, but I get its not always easy to machine to those tolerances

[DaveD44]

Thanks for a bunch of useful responses. Before I comment, some background. I've been building this locomotive (and now, tender) for many years, after finding a good set of castings that were for the most part untouched. But the one group of castings that had been messed with were the tender side frames and journal boxes, and the work had been done poorly. First, since wheels and their carriages (main driver boxes, trucks) on locomotives and tenders have to deal with quite a bit of unevenness and misalignment because of the tracks they have to traverse, I used Cagerol bearings--with barrel-shaped rollers that allow a fair amount of lateral runout. But whoever had messed with the tender trucks used these standard electric motor type bearings, so unless I had new journal box castings made (or went through a lot of trouble sleeving the ones I have) I had to go with what was already done. And since these ball bearings are in general use on live steam railroad cars, they should work.

The bearings were present and never used, but since they were at least 30 years old and some had visible rust and didn't turn well, I replaced them all. That's a thought for going forward, like MikeL46 suggested. I could use those until final assembly if it would not be too much trouble to grind the IDs.

But the journal box castings were also machined for a fairly tight fit on the bearing OD and since they are somewhat rectangular It would be difficult to chuck up eight of them individually to open up the bore. Perhaps someone has suggestions about how I could make that happen, perhaps by hand with emery cloth spinning with a wobble that would not matter? Then I could leave the bearings on the axles and pop them in and out of the journal boxes, finally giving them a dose of Loctite retainer when ready to roll. (Yes, I know that the outer bearing races should be a slip fit, but remember, these bearings have to help with truck dimensional stability.)

. . . for a .500" shaft, I would go with a .0002" to .0004" press fit. The standard of .0005" to .001" press fit per inch of diameter is a good rule. So .0004" would be on the tight side and .0002" would be on the loose side. These numbers are not too easy to hit. Keep in mind, that surface finish is related to size. With press fits, even more extremely so. If you have a coarse finish and do your measuring and you think you have everything right, just remember that you are measuring the peaks of the surface. Once you press on the bearing and press it off again, you will have knocked the peaks down into the valleys, and it will measure smaller. Most electric motor manufactures cylindrical grind their bearing seats on their rotor shafts. And for good reason. I figure most home shop guys will turn it oversize on the lathe and then polish the shaft to side with emery cloth. It hurts me pride to do this. So I have purchased some good lathes and even a few cylindrical grinders. That makes it easy with a cylindrical grinder. It actually makes it fun. A lot of fun running a cylindrical grinder and being able to take a tenth of a thou. I even bought an ID grinder because it titillates me so. . . .
--Doozer

I didn't mention this but yes, I plan to grind the axle shafts, both the wheel fit and the bearing fit, with my tool-post grinder. Like you, I love doing this as it best satisfies my appreciation of precision machine work. (Even better with my surface grinder and my DoAll cylindrical grinder that glues itself to the surface grinder chuck and even has a built-in sine plate--but these shafts are too long for the DoAll.) so with the tool-post grinder I can swing the compound rest over to a large angle and get mighty close to a tenth at a time additional metal removal. So it will be around .0003 over the ID. Does a nicely ground shaft bearing seat change the recommendation above to not assemble/disassemble and then reassemble the parts? Plus, the advice of eKretz and others to not press on the outer race to disassemble...

But that brings up a question: How do I accurately measure the bearing ID? I haven't had much success with that, even with some fairly expensive bore measurement tools, all too large. My smallest telescoping gage doesn't get me there with any repeatable measurements. Or can I assume that these "Made in USA" Nice bearings will all be close to an even 0.500 ID? The specs do state ID Tolerance -0.0005" to 0".

Rich Carlstedt (and others): Should I really trust a slip fit with Loctite retainer to hold up to heavy usage? And yes, the shafts are and will be 1018.

[Doozer]

... How do I accurately measure the bearing ID?...

Deltronic pins.

-Doozer

[Doozer]

...I didn't mention this but yes, I plan to grind the axle shafts, both the wheel fit and the bearing fit, with my tool-post grinder. Like you, I love doing this as it best satisfies my appreciation of precision machine work.

Killer dude!
You are doing it right.
Bravo ! ! !
A cut above.

-D