WOOD Magazine – October 01, 2019

woodmagazine.com 59

The basic straight bit

Use a straight bit for cutting grooves, dadoes

[Photo A], and rabbets [Photo B]. They come in

one-, two-, and three-f lute variations rang-

ing in diameter from^1 ∕ 16 " to 1". (Small bits

have room for only one f lute.) Larger bits

with two or three f lutes provide smoother

cuts, but at a slower feed rate. You’ll find

these bits in a variety of cutter lengths from

(^1) ∕ 4 " to 1 (^1) ∕ 2 ". Choose longer bits to cut deep
grooves, and when routing with a guide
bushing and template [Photo C].
Upcut and downcut spiral bits
When routing deep grooves or dadoes,
trapped sawdust can cause the bit and router
to work harder, overheating the bit, and
burning the walls of the cut. An upcut spiral
bit pulls out waste, similar to the way a stan-
dard drill bit evacuates shavings from a hole
[Photo D].
Sometimes a clean edge takes precedence
over clearing waste. In these cases, choose a
downcut spiral bit. As it spins, it begins cut-
ting on the top surface of the workpiece and
shears downward, preventing chip-out.
Because it tends to drive waste into the cut,
avoid burn marks by making a series of
shallow passes to reach final depth.
A compression bit combines the best of
upcut and downcut bits. At its tip, it upcuts
material while the balance of the length
shears downward. Use this bit when trim-
ming edges of veneered plywood or
melamine. Because each end of the bit cuts
toward the center of the panel, both faces
emerge chip-out free.
Tip! As a general guide,
make cuts no deeper
than the diameter of the
bit; for example, a
(^1) ∕ 4 "-deep pass for a
(^1) ∕ 4 "-diameter bit.

A

Learn more about

using guide bushings

on page 64. Guide bushing

Rout a groove or dado the width of the bit by making a single pass. Move the
guide, even just slightly, and make additional passes to widen the slot.

An edge guide adds stability when routing rabbets, as more than half of the

router may extend over the workpiece edge. Adjust the edge guide position to

plow wider or narrower rabbets.

When using a guide bushing that runs against a template, a long bit reaches

past the template to the desired cutting depth.

As an upcut bit spins, it

pulls debris up and out

of the cut. A downcut

spiral bit cuts from the

top down, shearing wood

cleanly. A compression

bit cuts from both ends

toward the middle.

B

C

D

Edge guide

Straightedge guide

1st pass

2nd pass