WOOD Magazine – October 01, 2019

woodmagazine.com 65

Bushing types and sizes

Guide bushings are short tubes (or barrels)

of various diameters and lengths, mounted

to a metal plate that fits in your router’s sub-

base and through which a router bit extends.

The bushing serves to space the bit a fixed

distance from a template or straightedge.

Most router subbases accept either univer-

sal bushings, also known as Porter-Cable

(P-C) bushings, or a proprietary bushing

[Photo A]. Universal bushings fit into a stepped

hole that’s 1^3 ∕ 8 " in diameter at the outer face

and^13 ∕ 16 " in diameter on the inner face. A

threaded ring locks it into the subbase.

Most guide bushings are referenced by the

outside diameter (O.D.) of the barrel. Uni-

versal guide bushings range from^5 ∕ 16 " to 1"

O.D. (Bosch has a guide bushing in one of its

kits with an O.D. of 1^3 ∕ 8 ".) The most used

bushing in my shop is a^3 ∕ 4 " O.D., but having

a full kit provides plenty of options. You also

need to know the inside diameter (I.D.) to

ensure that your selected bit will fit through.

Bushing barrel lengths run^3 ∕ 16 " to^5 ∕ 8 ". T he

barrel needs to be shorter than the thickness

of the template or straightedge so it doesn’t

rub on the workpiece. Because bushings are

brass or steel, you can grind them shorter, if

needed [Photo B].

If your subbase—and consequently your

guide bushing—sits off-center of the bit,

the gap between the bit and bushing is

larger on one side than the other, leading

to inconsistent results as you move the

router. To properly align the subbase, use

a centering cone, which is often included

in a router kit [Photo]. You can also find

accessory cones at most woodworking

stores, or use a chamfer bit if you stay

mindful of the bit’s sharp edges.

Buy a centering cone.

woodmagazine.com/centercone

Guide bushings come in three types. Most routers have or provide subbases that accept P-C bushings.

Bosch and Festool bushings fit only those router brands, but both manufacturers offer adapters that accept

universal bushings.

If a barrel projects too far, grind it down. Firmly grip the bushing with locking

pliers as you work.

A

B

Center the subbase on the centering

cone by taking advantage of the wiggle

room afforded by the panhead screws in

oversize counterbores.

SKILL BUILDER

Accuracy requires centering

Porter-Cable

(P-C)

Bosch

Festool