# Bearing Press Fit Tolerance



## LJP (Mar 4, 2015)

Hello All, have been away from machining for a while but looking to get back. Cabinetmaking pays the bills.

I am planning to build a 2" x 72" belt grinder for knife making (as well as general grinding). My plan is to use 1.375" OD x .625" ID bearings. 
On the  idler wheel (Aluminum) my press fit will be .0002 - .0004"  (bearing into wheel). This wheel will slip fit onto the shaft and be held in place with a flange and machine screw into the end of the shaft.
On the 10" contact wheel, I am making a housing to hold the 2 bearings. I will press the same bearings into each side of the housing, with the same tolerances. My instinct is that this shaft should have an interference press fit into the bearings as well. Then the contact wheel (slip fit) will be held on with the same arrangement as above.
My 2 questions:
Are my tolerances correct for press fit bearings?
Should the shaft be pressed into the bearings, that are pressed into the housing? At the same tolerance?
 Thanks, Larry


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## f350ca (Mar 4, 2015)

The interference sounds about right for the press fit, but if you go for an interference fit on the shaft as well you will need a spacer between the inner races to ensure you are not putting axial load on them while your pressing the shaft in.

Greg


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## LJP (Mar 4, 2015)

Thanks Greg, yes I see what you mean. I planned on pressing the bearings in, up to a shoulder. But I would have made the shoulder only the size of the outer races, Glad you mentioned the inner races, that does make sense! 
Larry


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## randyc (Mar 4, 2015)

All major bearing manufacturer catalogs specify the dimensions and tolerances for the bore and the shaft.  Having said that, as Greg indicated, your interference allowances seem reasonable.  (I don't know how you're going to measure the bore diameter accurately - that will be the tricky part.)


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## Plas62 (Mar 4, 2015)

I have never done any machining for bearings, but I have built a Grinder in a Box for my knife making hobby. All of the wheels I've bought from the knife maker supply houses the shafts, typically a bolt are slip fit and .500" .

Below are couple pics of my 2x72 it's setup for vertical or horizontal grinding.

There are two knife making forums I frequent  Knifedogs and Blade Fourms. If you go to those sites and search for grinder builds there is ton of information on the subject.

Good Luck with your build. Watch out knife making is an addictive hobby

Jim


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## LJP (Mar 4, 2015)

Jim, thanks for those pictures. I will check out those forums as well.
I have been designing this thing for a few weeks. It will be pretty much scratch built.
Grizzly sells a 10" contact wheel for only $76, it may be the only manufactured part I will buy.
I do like the horizontal, as well as the vertical version. 
The biggest problem is the floor space it takes up. 
I will start a build thread when I have something to show.
And yes, I may all ready be addicted.
Larry


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## outback00 (Mar 8, 2015)

Hello! I have a question. Everyone build 2" belt grinders, why not 3"? I am going to build a 3" but because all I see is 2" maybe I have miss something?


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## Plas62 (Mar 8, 2015)

I believe it is because there is a wider grit range available in the 2" x 72" belts. The 2" x 72" grinders are pretty much the "industry standard" for knife making from what I've seen.


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## Downunder Bob (Apr 2, 2017)

LJP said:


> Hello All, have been away from machining for a while but looking to get back. Cabinetmaking pays the bills.
> 
> I am planning to build a 2" x 72" belt grinder for knife making (as well as general grinding). My plan is to use 1.375" OD x .625" ID bearings.
> On the  idler wheel (Aluminum) my press fit will be .0002 - .0004"  (bearing into wheel). This wheel will slip fit onto the shaft and be held in place with a flange and machine screw into the end of the shaft.
> ...



generally bearings should not be fitted with interference fit on both ID and OD. in your application where teh bearings are fitted into wheels that are rotating, I'd suggest press fit the OD into the wheels, given that its in aluminium i'd give it a full thou even 1.5 thou  and have a neat sliding fit on the ID using a spacer as suggested by Greg, and a nut to nip the bearings up on the ID only. Think in terms of car front wheels.


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## StuNY (Apr 2, 2017)

When I built wheels for my 2x72 I press fit the outer bearing and slip fit the 1/2" shaft (bolt) and made a spacer from steel tube between the bearings as recommended above. I also used the 10" Grizzly wheel bored for bearings and recommend this approach highly- great value! I use this wheel a lot and it really can hog out steel fast with a coarse ceramic belt. One note, if you by chance miss measure a bore and it ends up more a slip fit than a press fit as I did on one of my 2" aluminum wheels, a little loctite 680 applied will work fine too- mine has held up for a couple years now.

FWIW I picked up these bearings on ebay and they have held up well on all wheels from 2" to 10", haven't replaced any yet.

1621 2RS Premium Sealed Bearings,1/2 x 1-3/8 x 7/16


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## mikey (Apr 2, 2017)

I would suggest you contact the manufacturer of the bearings you intend to use. The fits matter because they impact on internal bearing clearances, which in turn impacts on longevity. You will need to bore accurately to obtain the proper fits. As mentioned, you meed to install them so that pressure is applied to the race only to avoid brinelling.


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