Router bit bearing diameter change?

[David Ragan]

The router is probably one of my most underused tools. Have the handheld, trim, and table variety.

Also have some replacement bearing collars. Never used them. I look @ them and wonder if they will ever be used.

If a bearing seizes, that is a no-brainer. Replace it.

Are there any circumstances whereby you would you change the diameter of the bearing--the outer diameter, of course?

[Jerry Miner]

Most common, I think, would be changing a round-over bit to a beading bit and vice/versa (typically swapping 1/2" bearing to 3/8")

Rabbeting bits use different bearing sizes to create different rabbet depths.

[Robert LaPlaca]

Dave, I change bearing sizes all the time.. The previously mentioned rabbiting bits, slotting bits also, even use them on profiling bits to 'stage' cutting of the profile or slightly change the profile..

[Prashun Patel]

Here's what you have to be careful of with changing bearings on a rabbeting bit:

On some rabbeting bits, using a smaller bearing may cause a gap to exist between the bottom cutting surface end and the bearing. This can result in a torn out edge on the inside lip of the rabbet. I just encountered this when I used an undersized bearing on a 3/8" rabbet bit for a mirror frame I made. I thought I could take lighter passes and compensate for this, but that did not help. I had to use a larger bit.

It would have been fine to use a LARGER bearing on that bit, though (i.e., to make a smaller rabbet), because the bearing would have extended over the cutting surface.

I suppose the same problem exists on other profiles. All I'm saying is make sure your cutting edge extends all the way to whatever bearing you're using.

[Jerry Miner]

... using a smaller bearing may cause a gap to exist between the bottom cutting surface end and the bearing. This can result in a torn out edge....

Prashun--- I respectfully disagree. The bearing has little to do with tear-out. A typical slot-cutter, for example, does not have carbide extending all the way to the bearing. Nor do cope-and-stick bits. Tear-out is more a function of cutter geometry (and, of course, the wood being cut).

[glenn bradley]

I probably have a couple dozen bearings and rub-collars for various bits. If you are only using the original bearing you are correct in that you are not making full use of your router ;-)

- Varying existing profiles to make custom profiles on frames or other edges.
- Add bearings to bits that don't normally use them.
- Enlarging pattern cuts by specific amounts.
- Varying rabbet depths/widths.
- Purfling.

The use of larger and smaller bearings opens up your ability to put your imagination into action.

[Jim Mackell]

...........- Purfling.

The use of larger and smaller bearings opens up your ability to put your imagination into action.

How do you purfle with a router bit?

[glenn bradley]

How do you purfle with a router bit?


I probably used the wrong term. The shallow rabbets that make room for the banding(?) on guitars. A luthier where I used to work had bearings stepped in millimeters for this purpose. All our luthiers are probably laughing about now ;-)

[Prashun Patel]

You may be right. ou

I cannot explain, though why I got tear out when I used the smaller bit on my rabbeting bit but not when I switched back to the larger one.

The geometry of a rabbeting bit and the slot cutting bit should be similar right? I mean, both need to cut deep but leave a clean top surface as well. My bit is relatively dull, but I can't see that this has any 'bearing' on the outcome here... ;)

[Jerry Miner]

The diameter of the bit makes a big difference--changes the "exit angle" of the cut. Fibers are pushed more "sideways" than "straight out.

Sorry for the hi-jack everyone