# Router bit bearing using 16th" instead of mm



## Marco (Feb 21, 2009)

The short version..... The inside diameter of my router bit bearing is 8mm and want to know if using a 5/16" ID bearing will work and or any trick to snug it up a hair.

Thanks


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## PhilBa (Sep 25, 2014)

That's kind of on the edge. It's 2.7 thou off - a tad less than 1% (0.79%) larger. Given that a router runs between 12K and 24K RPM, even a small imbalance get's magnified. You might be able to wrap the shaft with 1.35 thou thick something - maybe two turns of aluminum foil but the trick is keeping it on the shaft when putting the bearing on. Anything that thin isn't going to be very stiff. Personally, I'd probably try it bare but I can't recommend others do it.


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## Stick486 (Jan 4, 2013)

Marco said:


> The short version..... The inside diameter of my router bit bearing is 8mm and want to know if using a 5/16" ID bearing will work and or any trick to snug it up a hair.
> 
> Thanks


no...
save the possible anguish and get a set of metrics...
you'll see more and more off shore coming in metric even though they are listed as imperial..


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## Nickp (Dec 4, 2012)

The larger ID of the bearing will make it spin to one side of its hole and create imbalance to the router when it spins up.

Definitely NOT...and don't try taping the shaft to make it fit...it will spin the tape...not a good idea.

I would suggest that nothing you put in there will keep it centered...

Can you use a guide bushing instead of a bearing...?


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## Marco (Feb 21, 2009)

Nickp said:


> Can you use a guide bushing instead of a bearing...?


For the purpose no. I had planned to use the 1/4" slot cutting bit on the table cutting a slot in a dry fitted box joint box as Phil had suggested. The bit I am wanting to use was bought a few years back for a different application and assumed I could get different bearings later on as needed. A 1 1/2" bearing brings the depth of cut to a 1/4" and a 1 5/8" bearing to an 1/8" depth.


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## Nickp (Dec 4, 2012)

Marco said:


> For the purpose no. I had planned to use the 1/4" slot cutting bit on the table cutting a slot in a dry fitted box joint box as Phil had suggested. The bit I am wanting to use was bought a few years back for a different application and assumed I could get different bearings later on as needed. A 1 1/2" bearing brings the depth of cut to a 1/4" and a 1 5/8" bearing to an 1/8" depth.



Would the fence not work for you to adjust depth of cut...? Maybe I'm missing what you're trying to do...?


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## Marco (Feb 21, 2009)

I had planned to use the 1/4" slot cutting bit on the table cutting a slot in a dry fitted box joint box as Phil had suggested. Cutting the slot in that manner prevents the slot being over cut and able to be seen on the exterior of the box. If the joints were mitered the easy way would be the fence and just run your 4 sides through and adjust the depth with the fence. With a box or dovetail joint it can be done using a fence but would be a P.I.T.A. starting and stopping each side at the right point.


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## Nickp (Dec 4, 2012)

Marco said:


> I had planned to use the 1/4" slot cutting bit on the table cutting a slot in a dry fitted box joint box as Phil had suggested. Cutting the slot in that manner prevents the slot being over cut and able to be seen on the exterior of the box. If the joints were mitered the easy way would be the fence and just run your 4 sides through and adjust the depth with the fence. With a box or dovetail joint it can be done using a fence but would be a P.I.T.A. starting and stopping each side at the right point.



You could put two stops or two marks on the fence...then push the box into the bit at the starting point, run the box along the fence until you hit the stop point and pull the box away from the bit...


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## Marco (Feb 21, 2009)

Well the 1-1/2" bearing came in and there was no noticeable difference between the 8mm id and the 5/16 id in hand or on the router at 8 to 
10,000 rpm. It cut a nice 1/4" slot a 1/4" deep. The problem with using such a big bearing with this application is it doesn't cut far enough into the corners of the box. My solution was undo the dry fitted box and hold each side and each end up to the bit and run it up a little so that a squared piece will fit. I'm not suggesting anyone to do this but for me there was not a safety issue.

Make note "Don't Try This In Your Shop" as stated by others have the exact size bearing to fit the bit and don't hold a piece of would with your hand to make a cut as stated above.


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