Need some press fit bore diameters/tolerances for ball bearing.

Wild West · Nov 8, 2017

I have gone to a few bearing sites but none seem to list the manufacturing tolerances nor do they have a recommendations for press fit tolerances. The bearing is 28mm OD (1.1024") x 12mm ID x 8mm W.. Material to be pressed into: 6061-T6511 alum. Does anybody have any data as I need to purchase plug gages for a production run.

Thanks

sfriedberg · Nov 8, 2017

You're not looking at the right documents. Every serious bearing maker has comprehensive documentation for recommended/required bearing fits, absolutely with tolerances.

You may not find this info just on a Web page. You may have to download the technical catalog or application guides. For example, here's data from NSK. See Section 8, beginning on page A153.

HuFlungDung · Nov 8, 2017

Probably .0005" max interference. But 0 clearance is also tight enough that you need a light press to install. I fit bearings for a living, and you generally can't slide them in until you've got .0002" clearance. I'd think that goes for a pin gage as well, So size your gages accordingly, from .0002" over to .0003" under.
The bearings I've worked with over the years are in the range of 'on nominal dimension' to .0002" undersize on the OD. That is quite a bit of variation when it comes to tolerance stackup but maybe you can acquire a batch of bearings and customize the tolerance a bit according to the batch's OD.

Richard King · Nov 8, 2017

Call your bearing distributor and ask them. They have charts on that. If not they can call the bearing MFG to get that info.

Milland · Nov 8, 2017

Operating temperature as well as surface roughness of the bore play a role in how much hoop stress the bearing will see while in use. Make sure to factor these in if there's criticality to the bearing function.

Also, most deep grove bearing can be purchased in a range of internal clearances to accommodate fitting requirements. A bearing that must be very firmly held can be bought will larger inside clearance, and is brought to nominal by compression after installation.

Wild West · Nov 8, 2017

Ok, these are cheap import bearings that my customer buys by the 10,000's. They are used in wheels for standup scooters for kids. The wheels are machined from billet. The customer doesn't know what he needs so he leaves it to me to figure out and then he'll second guess me.

Erich · Nov 8, 2017

The bearings are still manufactured to industry standard sizes, so another mfgr engineering sheets will work.

You are doing Design work for your customer, make sure you are billing him engineering rates not machining rates for the work.

HuFlungDung · Nov 8, 2017

Wild West said:
Ok, these are cheap import bearings that my customer buys by the 10,000's. They are used in wheels for standup scooters for kids. The wheels are machined from billet. The customer doesn't know what he needs so he leaves it to me to figure out and then he'll second guess me.

Loctite is his/your friend, too. That way you can err on the looser side and still get away with it.

Milland · Nov 8, 2017

HuFlungDung said:
Loctite is his/your friend, too. That way you can err on the looser side and still get away with it.

That usually requires a decent cleaning of the bearing and bore for best adhesion. In the OP's situation, if he's making the billet wheels and getting a good finish on the bore (so you're not getting a "false diameter" reading by measuring only the peaks of the rough surface), I'd shoot for a .0012 to .0015" interference with the bearing. It's a little tight in some circumstances, but should prove reliable and not fall out unless really poor insertion technique leads to shearing away material during pressing.

If the scooter wheels are mounted one-sided, I'd be more nervous about failure modes. If used in a typical fork or otherwise constrained mount, having a wheel fully detach isn't as worrying. Don't want a lawsuit when Junior loses a wheel while cruising down mount McKinley...

AlexO · Nov 8, 2017

Wild West said:
Ok, these are cheap import bearings that my customer buys by the 10,000's. They are used in wheels for standup scooters for kids. The wheels are machined from billet. The customer doesn't know what he needs so he leaves it to me to figure out and then he'll second guess me.

The "cheap" means all bets are off. Some sort of bearing retaining compound is in order. Otherwise, the C classes tell you all you CAN know.

AlexO · Nov 8, 2017

Milland said:
If the scooter wheels are mounted one-sided, I'd be more nervous about failure modes. If used in a typical fork or otherwise constrained mount, having a wheel fully detach isn't as worrying. Don't want a lawsuit when Junior loses a wheel while cruising down mount McKinley...

There surely is some sort of retainer there...

gbent · Nov 8, 2017

Plug gauges are not adequate for bearing fits. You need setting rings and bore gauges.

Sparky961 · Nov 8, 2017

I regularly set up and monitor bores for interference fit bearings with a digital internal mic. Mine is a Fowler branded unit, so nothing fancy or crazy expensive. I've been able to keep them consistent within what I can measure. I own a 0-1 and 1-2, which covers most of the bores I create. Beyond that I make do with telescoping gauges and an outside digital mic, which actually work pretty well and consistently together if used properly.

The "rule of thumb" that I've heard more than once is 0.001" of interference per 1" of diameter. It's worked pretty well for me in cases where I've used it. But also note that my criteria for success is based on the feel of insertion while using a large floor stand arbor press, and whether it spins freely when I'm done.

HuFlungDung · Nov 8, 2017

Sparky961 said:
I regularly set up and monitor bores for interference fit bearings with a digital internal mic. Mine is a Fowler branded unit, so nothing fancy or crazy expensive. I've been able to keep them consistent within what I can measure. I own a 0-1 and 1-2, which covers most of the bores I create. Beyond that I make do with telescoping gauges and an outside digital mic, which actually work pretty well and consistently together if used properly.

The "rule of thumb" that I've heard more than once is 0.001" of interference per 1" of diameter. It's worked pretty well for me in cases where I've used it. But also note that my criteria for success is based on the feel of insertion while using a large floor stand arbor press, and whether it spins freely when I'm done.

That is a pretty heavy fit, more suitable for plain bearings, bronze bearings and sleeves than for rolling bearings. A tapered roller bearing cup could also be installed with that 'rule of thumb', but ball bearings don't need that. If you're that fearful of something coming apart, you need to add a retainer to the design.

An aluminum housing is fairly easily damaged, too, with a heavy press fit. If it is thin wall, it may crack, if heavy wall, it may score and gall up.

Sparky961 · Nov 8, 2017

HuFlungDung said:
That is a pretty heavy fit, more suitable for plain bearings, bronze bearings and sleeves than for rolling bearings. A tapered roller bearing cup could also be installed with that 'rule of thumb', but ball bearings don't need that. If you're that fearful of something coming apart, you need to add a retainer to the design.

An aluminum housing is fairly easily damaged, too, with a heavy press fit. If it is thin wall, it may crack, if heavy wall, it may score and gall up.

Agreed. What I didn't mention is that I err on the lighter side of that "rule". After reading this thread, I'll be seeking out and paying more attention to manufacturers' recommendations.

TedinNorfolk · Nov 9, 2017

I've mentioned this elsewhere on this theme-look up Rok-it gauges. For regular bearing work I wouldn't use anything else.

plastikdreams · Nov 9, 2017

Little ot, what material are the wheels made from?

eKretz · Nov 9, 2017

Sparky961 said:
Agreed. What I didn't mention is that I err on the lighter side of that "rule". After reading this thread, I'll be seeking out and paying more attention to manufacturers' recommendations.

Definitely do not follow the. 001" per inch rule with ball bearings if you want good bearing life. Especially in smaller bearings like you're using, this would be a kiss of death. I understand about not wanting the bearings to come loose while Junior is rolling down Mt. McKinley, but you don't want them to overheat and lock up the wheel either. Junior's mommy and daddy will sue either way. There is a reason that bearing manufacturers provide this data... Use it!

Wild West · Nov 9, 2017

Erich said:
The bearings are still manufactured to industry standard sizes, so another mfgr engineering sheets will work.

You are doing Design work for your customer, make sure you are billing him engineering rates not machining rates for the work.

This customer gives me lots of very profitable work so I throw in freebies. This will turn out to be an order of 1000's for me. I usually make $100-$150 on them with out breaking a sweat.

Wild West · Nov 9, 2017

Sparky961 said:
I regularly set up and monitor bores for interference fit bearings with a digital internal mic. Mine is a Fowler branded unit, so nothing fancy or crazy expensive. I've been able to keep them consistent within what I can measure. I own a 0-1 and 1-2, which covers most of the bores I create. Beyond that I make do with telescoping gauges and an outside digital mic, which actually work pretty well and consistently together if used properly.

The "rule of thumb" that I've heard more than once is 0.001" of interference per 1" of diameter. It's worked pretty well for me in cases where I've used it. But also note that my criteria for success is based on the feel of insertion while using a large floor stand arbor press, and whether it spins freely when I'm done.

Once in production, I'll use XX class Go-NoGo plug gages.

Need some press fit bore diameters/tolerances for ball bearing.

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