68 - Our All-New Router Jig, страница 14

FEATURE PROJECT

Tapered Bed

OVERVIEW

Hie mortising machine can be broken down into three main com-ponents: a tapered bed, a sliding table, and a carriage. These three miter components work together in such a at 75⁰ way that they allow you to easily ^ adjust the length and depth of the / mortise, as well as its location on the thickness of the workpiece.

The bed is the foundation of the mortising machine, so I built it first. It's made up of two tapered sections, just like the bed on a jointer. Turning a knob at the end of the bed causes the upper section to slide against the lower section, raising or lowering \ the overall height of the bed and the workpiece (see photo at left).

Base - Before making the tapered sections of the bed, I cut out

ADJUSTMENT^ BLOCK \

hole locations for hooks

UPPER SIDE

NOTE: to-i.....

channel is snug against outside face

aluminum channel

LOWER SIDE

#12 screw hook

⁵/i₆"-dia. hole with counterbore (refer to ^ fig. 10a)

k Height Adjustment.

Turning a knob at the end of the tapered bed will raise or lower the sliding table.

NOTE:

all pieces are ³/₄" plywood

a piece of ³A^U plywood for the base (A), as you see in Figure 1. Then you can cut an opening near the front of the base and lay out and drill the screw holes that are shown in Figure 1. (The opening in the base is to allow you to assemble and make adjustments to the sliding table that will be added later.)

The tapered bed sections are made by cutting four identical tapered sides (B) from ³A" plywood. In Figure 2 you can see how I used a simple jig on the table saw to cut the tapers. (The jig is also shown at left in the margin drawing.) After the

pieces are cut, you'll also need to drill a hole in each one for an adjustment block that is added later.

To allow the tapered sections of the bed to slide smoothly against each other, I used some aluminum channel. The channel is attached to the bottom edge of the upper tapered section so that it fits over the edges of the lower section, just as you see in Figure lb.

The aluminum channel also helps to keep the upper and lower halves of the bed flush and aligned. But in order for this to work, the channel needs to be accurately positioned on

the edges of the upper sides. To do this, I used the top of my table saw as working surface, as you see in Figure 3. Carpet tape is used to hold the channel in place while you drill pilot holes and screw it down.

Adjustment Blocks - Each pair of sides is connected with an adjustment block (C). These are just a couple of rectangular pieces of plywood. Each block will be held in place by just two screws, one on each side. This allows the adjustment blocks to pivot as the two tapered bed sections slide against each other (Figure 6).

FIRST:

drill six countersunk holes in channel

channel rests on lower side

SCOND: tape

and screw channel to bottom of

upper side

^ ^_/

#6 x Fh woodscrew

NOTE:

drill pilot holes

for screws

^ Vie" x⁹/16" x alum. (I6V2"

mitef slot

V_

14

ShopNotes

No. 68