Router bit sizes

[Amy Leigh Baker]

Hey guys,

Can someone explain to me the difference between router bit sizes? Not the shank, but the profile, such as 1/4" roundover bit versus 3/8" roundover bit? I need a flushtrim bit, and these also list sizes. It seems to me the same flush-trim bit would accomplish it's goal on any size wood, but I guess I am wrong. This is what I will need bits for...


Flush trim bit to trim off the excess trim off the top of a box. The trim is about 1/16" thick, and it is mounted on 3/4" oak ply. Is there a particular size flush trim bit I would need?
What size roundover bit would I need to produce the edge on this tabletop. The top is 3/4" thick... http://sawmillcreek.org/attachment.php?attachmentid=83339&d=1204687844
I need to make a mortise in a 3/4" piece of red oak. The mortise will be about 26"L x 2 1/4"W x 1/4"T. I assume a straight bit would be appropriate, but what size would I need, and would a straight bit cut the wood when I plunge the router?I don't have the money to just buy router bits and experiment or I would. I just need to buy what I need at the moment.

Thanks!

Amy

[Charles McCracken]

Amy,

The size of the roundover you use is largely a matter of taste but here are answers to your questions:

1 Use the largest diameter flush trim you can for the application to get the best results. Usually the limiting factor is for inside radii. They generally range from 1/4" to 3/4" diameter.
2. It appears from the picture that you have a full quarter round on 3/4" material so you will need at least a 3/4" radius roundover to accomplish it. Be aware that a 3/4" radius roundover on 3/4" stock will leave nothing for the bearing to follow so it should be done on a router table with a fence to guide it.
3. For the mortise you should again choose the largest diameter you can find/afford. Some claim to plunge cut but all straight bits work best when "ramped" into the cut to start.

[Greg Hines, MD]

For your mortising operation, you can use a straight bit, but you really need to either ramp in, or use a drill bit first, as a traditional straight bit will not cut a very good mortise. A better choice would be either a "mortising bit" which has extra carbide cutters on the end/top of the bit, or a spiral bit. That is my choice for that kind of work, particularly an upcut shear bit. They leave a good mortise, and clear out the chips good through their action.

As to your round-over, that is a personal choice. a 3/8" or 1/2" radius will leave you a good looking edge. There are also plenty of wavy edge bits specifically for table tops or chair rails that would look good as well.

You mention not being able to get a bunch and experiment. There are plenty of sets out there that have several bits for a good price. You might want to look into that too. Woodcraft also sells good 1/2" shank bits every now and then for $5 a piece, and their sets can be had for the same price from time to time.

Doc