needle roller bearing size/fitment

[z28]

Hello,
I am drawing up a part in solidworks. The drawing is done other than I cant figure out what size bore I need for a 21x27x15 7e-hvs nkn needle bearing. Ive searched all over the web. I assume I need a 27mm bore but Im not sure the + or - tollerence I need for the correct fit. When I have the part machined I dont want to get the part back and not have the bearing fit correctly.

Thanks for any help.

[RICHARD ZASTROW]

Try this for info: http://www.ntn.co.jp/english/product...f/NB-HB_en.pdf

Dick Z

[keebler303]

Whenever I need really close fits, I send the bearing, shaft, bushing, tube, etc. along with the drawing and say "make it fit that". They can make it fit nice without much trouble, instead of having to specify some ungodly tolerance to get what you need.

My $.02
Matt

[RICHARD ZASTROW]

What happens when you must replace the bearing? I'll use the tolerances provided by the bearing manufacturer.

If the grinding source can't hold the tolerances, it's the wrong source.

Just my opinion. Dick Z

[keebler303]

Dick

You are correct, however, if the first bearing is within tolerance, the hole to fit it is going to be pretty darn close for the next bearing anyway. Even cheap bearings are within a few ten-thousandths of an inch. Its a lot easier to get yourself in trouble when you start specifying fits you don't know how to design. If you tell the machinist you want a slip fit or a press fit, that is what you will get, and there will be no question if the bearing fits because it can be checked before it leaves the shop.

Another penny or two
Matt

[RICHARD ZASTROW]

Matt, I guess I'm spoiled. LOL The grinding I get for spindle bearing fits are in MICRONS. Visualize half-tenths. Not cheap but worth it.

You'll find the more precise the bearing, the more precise the fits.

I'm working on the design for a 20,000 rpm grinding spindle right now. It's driven by a 27kw (36hp) motor. It will use ABEC 9 ceramic angular contact bearings.

Tolerances for the shaft and housing are +/- 3.5 microns (.00014"). The grinder guy asked if I'd prefer holding it to the high or low side!!!!!! LOL

I agree this is not for the DIY home shop. Typically you can probably get away with ABEC 5 and then the tolerances for the bearing dimensions open up a bit as well as the shaft and housing dimensions.

Fun stuff.

Dick Z

[keebler303]

Without knowing what the "part" is, one can only assume what its use may be. Could be bearings for a wheelbarrow axle for all we know, I think ABEC9 might be a bit overkill for that. I don't even want to ask how much ABEC9 bearings cost.

Cheers
Matt

[RICHARD ZASTROW]

Matt, you're right,they are EX$$$$$$$$$$$$$$$$$PEN$$$$$$$$$$$$$$$$IVE!!!!!

The other major problem is availability. I can't specify bearings that are made twice a year in quantities of 10 pairs. Client might be a bit PO'd if he has to wait 6 months for a replacement.

Just another compromise. I could order an extra set and keep them on the shelf just in case we need them.

Dick Z

ps; I think I've wandered off the original question.

[handlewanker]

Hi, with a needle bearing of 27mm OD, if you make the bore of the housing tight, that is minus a thou or -.02mm, then you'll get a corresponding reduction in the bore of the needles and this will impact on the spindle it rides on.

It's difficult to measure the bore of the needle bearing, (unless you make a plug gauge) unlike the bore of a regular ballrace, so you'd best get the spec sheet and check the manufacturer's recomendation, otherwise all you can do is to measure the OD of the neeedle bearing shell and make the bore of the housing it's going into a light press fit, e.g. one thou per inch of diam for press fits.

The 21 mm inside diam of the needle bearing must allow for the press fit in the housing, and if the shaft it runs on is 21mm diam, the manufacturer would have to make the needle inside diam bigger by that press fit amount, otherwise the shaft must be made undersize to fit it.

The conundrum occurs when the needle bearing is made a push in fit and is Loctited into the housing, which will make the needle bearing a loose fit on the shaft, unless the shaft is made an odd size (bigger) to allow for that.
Ian.

[RICHARD ZASTROW]

z28, I've tried to find info on NKN needle bearing dimensions with no luck. Then tried other manufacturers but nothing on 21 x 27 x 15 size.

Can you possibly change to a standard readily available size? Sorry, I can't help as is.

Dick Z

[Catfish Dinner]

Originally Posted by RICHARD ZASTROW z28, I've tried to find info on NKN needle bearing dimensions with no luck. Then tried other manufacturers but nothing on 21 x 27 x 15 size. Can you possibly change to a standard readily available size? Sorry, I can't help as is. Dick Z

I found this thread through Google.

Do you have those bearings? 27 bore 21 shaft 15 width

I need that exact size for suspension linkage. I only need 2 bearings but I can oly find a kit that includes everything.


Edit: Ooops, sorry I quoted the wrong post.