On 4/25/2010 3:22 AM, Bill wrote:
I wish to cut 1/2" wide mortises all the way through a fourbyfour (cutting
from both sides of course). Was just about to order the Amana bit# 45426
which is a double-fluted straight plunge bit, with 1/2" shank, 1/2" cutting
diameter and a 2" cutting height.

Will use a DeWalt 2.25HP Router. Is the above bit adequate for this job
(or do I need to look at spiral-fluted)? Just because the bit has a 2"
cutting height doesn't mean I should plan to try to cut more than 3/16 to
1/4" at a time, right?


BTW, Swingman, you were right--there are more bits than I thought out there!
I assume that since I have a plunge router that I'll be able to extend the
abilities of a single bit a little. For instance, using a bit with 1.5"
cutting height to cut a 1" deep groove. I know, of course, that one should
not use a bit that is too much longer than necessary due to deflection and
vibration, etc. I don't have any router bits at all yet, and my router
hasn't even arrived yet, so I sure I'm destined to learn a great deal! I
can try my hand at chisel-sharpening in the meantime.. Probably should dust
off Bill Hylton's book (on the router) on my shelf...

Just make sure that you have positive control of the router cutting
holes that deep--if you don't, it's easy for the bit to grab, rattle
around a bit, and break.

By positive control I mean a jig that doesn't let the router move any
direction but the direction you want it to, with no play to speak of.
Don't rely on hand pressure against a fence.

Found that out the hard way.

While spiral bits are wonderful in many ways, I wouldn't use one for
deep mortises until I was sure I could do them reliably with a straight
bit--the reason is that they cost a lot more than straight bits and
being solid carbide they're easier to break.

Learned that part the hard way too.

The jig doesn't have to be anything elaborate--you can cobble one up out
of a scrap of plywood and a couple of pieces of 2x4 that will do the
job, but it has to keep the router under control. If you need a mortise
wider than the bit, offset the router in the jig a little bit, then
reverse the jig to get your second cut (and do that for each step of
depth, don't cut all the way through then try to widen it--you may get
away with it but it's asking for trouble).

And as Allan Quatermain said to Tom Sawyer, "take your time, you've got
all the time in the world".