# Advice on press-fit bearings



## Drhender (Dec 11, 2018)

I am mentor for a high school robotics team and need some advice on of fitting bearings.  Our drive and wheel shafts run in a 1-1/8" flange bearing, housed in either the wall of 1x2" aluminum rectangular tube (1/8" wall) or in a 1/4" aluminum plate.  We recently purchased a CNC router table and have been getting really good results/precision.  We'd like to buy a reamer to perfect the fit of our bearings-- the CNC gets it really darn close, but I know a ream would really bring it home.  What size reamer should we be looking for?  1.126, 1.124, or dead on 1.125?

Also, same question for a smaller bearing: I am told it's a 7/8" OD, but my guess is that it's really 22mm.


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## Mitch Alsup (Dec 11, 2018)

http://www.bearing.co.il/FITS06.pdf

For a 1.125 shaft:: a JS5 slight interference fit wants 0.000,2" interference.

Bearing fits are not done in thou they are generally done in tenths.


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## Drhender (Dec 11, 2018)

Ok, but can I buy a 1.1248 or 1.1252 reamer? We’d rather not spend hundreds on a couple of reamers. 

Is 0.0002” 2 tenths larger than the bearing diameter?


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## mmcmdl (Dec 11, 2018)

Bore them to size . Or , buy the nominal size reamer and stone the edge in a lathe . If you knock .0001 off each edge you have your 2 tenths press fit .  They also sell adjustable blade reamers !


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## mattthemuppet2 (Dec 11, 2018)

2nd bore to size. I wouldn't even consider reaming at that size.


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## dulltool17 (Dec 11, 2018)

mattthemuppet2 said:


> 2nd bore to size. I wouldn't even consider reaming at that size.


Yeah 1-1/8, regardless of the tolerance, is a pretty big reamer for hobby-shop work.

Hate to phrase it this way, but I'd be boring.


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## Mitch Alsup (Dec 11, 2018)

dulltool17 said:


> Hate to phrase it this way, but I'd be boring.



Machinists are always boring something!


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## Drhender (Dec 11, 2018)

Wow, I appreciate all of the advice!  

Boring requires a lathe or a mill. We don’t have either. I was hoping to get away with reamers in a drill press. However, our drill press isn’t a particularly precise piece of machinery. Is attempting to ream beyond our capabilities?


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## Alexander McGilton (Dec 11, 2018)

It's easy to get caught up with the professional documentation and be preparing tolerances intended for precision machinery. Stay away form high 
ABEC number as a few microns of bearing play is nothing to worry about for your purposes. 
I don't know if you have a milling machine with boring head or should your parts be small enough to to be turned on a lathe face plate, so reaming may be your only option.  

Go for the ABEC-1 or non rated bearings in inch sizes. Measure the bearing, set the reamer to size .001  under and use precision ground shafting or drill rod for you shafts.  Looking at the generic flange bearing, the tolerances of the bearing are way too loos to warrant the tolerances mentioned above. https://www.mcmaster.com/6383k234

Adjustable reamers would be the easiest way to go
http://www.grizzly.com/products/Grizzly-11-pc-Adjustable-Reamer-Set/H5942
These you can set to size with the aid of a micrometer. Tighten a tap handle at the stub, set a presision square to the blades and the work, then ream by hand.


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## P. Waller (Dec 11, 2018)

The press fit that a radial ball bearing will tolerate, (I assume that you are using ABEC 1 off the shelf radial bearings, assuming is never a good idea however) is dependent on it's size and internal clearances.
You will find that an ABEC1 annular ball bearing of say 1/2" OD will have a visible clearance if the outer race is held in one hand and the inner race is wiggled by the other hand, try it.

On a practical note if the press fit does not exceed the internal clearance then you are good to go. If you are trying to create an annular ball bearing bore using circular interpolation in a CNC router pressing the outer race into a bore with the typical 12,3,6 9 o'clock deviations will often cause the outer race to become out of round.


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## Forty Niner (Dec 11, 2018)

Other options:
1) Go ahead and buy the 0.001 undersized reamer, then hone the fit to size.  It won't take much to get it to the size you want. 
2) Buy the on size reamer and mount the bearing with loctite.
3) Buy the 0.001 undersized reamer and press a bearing in and see how it turns.  My hunch is that the aluminum you are mounting the steel bearing in will give more than the steel and you will be OK making that bore .001 undersized.


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## mattthemuppet2 (Dec 11, 2018)

Drhender said:


> Wow, I appreciate all of the advice!
> 
> Boring requires a lathe or a mill. We don’t have either. I was hoping to get away with reamers in a drill press. However, our drill press isn’t a particularly precise piece of machinery. Is attempting to ream beyond our capabilities?



without either a lathe or a mill you're best off using the nearest holesaw/ annular cutter you can get, then using tolerance rings or Loctite bearing retaining fluid.


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## 4ssss (Dec 11, 2018)

Sweat the bearing on the shaft


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## Drhender (Dec 11, 2018)

@mattthemuppet2 I am sure we can do better on the CNC than we can with a hole saw. 

@4ssss , the shaft to bearing connection was never in question. We use hex shaft, so I am not concerned about that.


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## Drhender (Dec 11, 2018)

@P. Waller your concern about out of round holes due to interpolation on the CNC is another reason we were considering using a reamer. 

I think what I am hearing is that a spot on reamer should work pretty well but may require a touch of locktite. Another promising alternative is a reamer a thousandth under and  hope that the press fit works. In the aluminum rectangular tube with 1/8” wall, I think it’s unlikely that the press would create enough pressure to over compress the steel bracing race. The 1/4” plate aluminum might be a different story. 

Again, thanks for all of the advice!


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## mattthemuppet2 (Dec 12, 2018)

Drhender said:


> @mattthemuppet2 I am sure we can do better on the CNC than we can with a hole saw.



right, forgot about that. Same applies, but now with more precision


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## mikey (Dec 12, 2018)

Interesting discussion. Bearing fits can be tricky, depending on the precision of the bearing especially. If I understand correctly, you are trying to press fit a flanged bearing (the kind with just the flange and no external flange with bolt holes) into the end of a square aluminum tube or a hole in 1/4" plate.

I suspect that the bearing will not stay in place in a tube, loctite or no, if all you're relying on is a press fit. You only have contact with the bearing at four small contact points and I don't think it will stay in place. Could be wrong but I wouldn't try it.

You might get away with it in plate. Probably the best option would be either a line-to-line fit (bore size = OD of bearing) or perhaps 0.0002" under at most if you want to minimize the impact of the bore on internal bearing clearances. Here, you are talking about a bore with really tight tolerances and I'm not sure you'll do that with a reamer in a drill press. There is a good deal more to reaming with accuracy than it might seem. I'm attaching a doc below that might shed some light on this.

If I had to do this, I would contact the bearing manufacturer and discuss it with them. If internal bearing clearances are pretty loose then I would try to use your CNC router to get the bore dead on size at 1.250" and try for a line-to-line fit and use loctite to lock it in. A precision reamer of this size would be expensive so unless your budget allows for it and some experimentation, I would not do that.

Another option is to take your stuff to a machine shop and see if they will bore the plates for you because that is really what you need here. Explain that its for the kids and I bet they will be most cooperative.

A final option is to buy flanged bearings with external plates with bolt holes. This eliminates the need for a precision press fit, is stronger and changing the bearings is simpler.


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## middle.road (Dec 12, 2018)

If it's not mission critical or going to Mars, this is after all aluminum. If the CNC router is any good, setup a test plate, try sneaking up on it and then see what the results are.
As mentioned above, Loc-Tite can be your friend here if you're not shooting for super high precision.
Heck #660 can fill quite a gap.


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## Drhender (Dec 12, 2018)

Just for clarity, I've added an image showing the mounting of one of the bearings in the rectangular aluminum tube.  (As you can see, we anodize all of our aluminum in a nice blue color .  Additional clarification-- the flange bearings are a standard part in the competition robotics world - FIRST Robotics Competition (FRC).  We _could_ go looking for a similar flange bearing with a larger mounting flange and screw holes, but the likelihood of finding them that match both the outer and internal hex dimensions for a reasonable price is low.  For that reason and for the sake of staying with a standard part, we will probably no change.

From all of your comments and advise, I believe the biggest take away is to use loctite. . We will probably get as close as we can with the CNC and then press fit with loctite for insurance.  I still may try to find a reamer we can use to hand ream to ensure that the holes are round and consistent in diameter, but we will likely have to do some practicing to see if we can learn to hand-ream with some precision.

Thanks again for all of your advise!


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## TQA222 (Dec 13, 2018)

What about trying a shrink fit? Rule of thumb says 1 thou per inch.

Or look it up in "Machinery's Handbook" 

Ali in the oven Bearing in the fridge.


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