Half-Blind Dovetail Procedures

CHAPTER 11
Half-Blind Dovetail
Procedures
80
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
Chapter Foreword.
VERY IMPORTANT …READ THIS!
About Half-blind Dovetail cutter depth, and board thickness.
It's important to understand that you need to select a specific dovetail cutter
for your half-blind dovetail project, depending on the pinboard thickness
you are using. In other words, bit selection is critical. Here's why:
■
Half-Blind Dovetail bit selection is
based on the thickness of the pin
board (drawer front). Choose a bit for its cutting
depth specification. Its specified cutting depth must
always be less than the thickness of the pin board.
■
A dovetail bit used for Half-Blind Dovetails will produce only ONE SPECIFIC CUTTING DEPTH.
You can make small cutting depth adjustments
(±1⁄ 64") to achieve perfect joint fit ...but not to alter
joint design.
■
All Half-blind pins and tails must be routed with the
SAME BIT, and at the SAME DEPTH OF CUT.
■
All Half-blind dovetail bits work with the 7/16" O.D.
template guidebush supplied with your Leigh jig.
■
Only 1⁄ 2"[12,7mm] diameter bits can be used for halfblind dovetails.
The following pages and Appendix II have detailed descriptions of all Leigh
Half-blind dovetail bits.
81
11-1
Half-blind Dovetails:
 Pins h
 Pin sockets
 Half-pins
 Half-pin sockets
 Tails H
 Tail Sockets
The pins fit in the pin sockets. Joints should almost
always end each side with
half-pins.
£
È
Î
x
{
Ó
11-2
Ó
£
Pinboard thickness  determines
the maximum depth of cut ➁
you can use. Select a bit with a
specified cutting depth that is less
than the pinboard thickness. Only
1⁄ 2"[12,7mm]
➂ diameter bits can
be used for half-blind dovetails.
Î
Minimum Pin Board
Thickness
1/2" [12,7]
Cutting
Depth
3/8" [9,5]
Dovetail
Bit No.
No.128-8
9/16" [14,3]
7/16" [11,1]
No.120-8
5/8" [15,8]
1/2" [12,7]
No.112-8
3/4" [19]
5/8" [15,9]
No.101-8
7/8" [22]
3/4" [11,1]
No.80-8
Numbers in brackets are millimetres
Guidebush
Diameter
7/16" [11,1]
Use this chart to select a Halfblind Dovetail bit to suit your
pinboard thickness. For full bit
specifications see Appendix II.
82
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
11-3 Joint Fit and Depth of Cut
1
PIN
3
Remember that a half-blind dovetail bit can
only produce one perfect depth of cut in your
layout. If you want a different depth of cut,
you must use a different bit.
Here’s why the depth of cut  changes the fit
in half-blind dovetails. Increasing or decreasing the depth of cut does not affect the pin
socket width , but does affect the width of
the pin  that goes into the socket .
2
11-4
1
3
Note that decreasing the bit depth  makes
the pin  narrower while the pin socket 
stays the same width, producing a loose fit.
Decreasing the bit depth (i.e. raise the bit
into the router) produces a looser fit.
2
11-5
1
3
Increasing the bit depth  makes the pin 
larger while the pin socket  stays the same
width, producing too tight a fit.
Increasing the bit depth (i.e. lower the bit)
produces a tighter fit.
2
83
11-6 Bit Angle and Depth of Cut.
8˚
Both the pins and tails of a half-blind joint are
routed using the same dovetail bit, with the
same guidebush and at the same depth of cut.
1
The only way to select a different depth of cut
is to use a different angled bit. Leigh provides
five different angled dovetail bits for a range
of cut depths. The lesser the angle, say 8˚,
the deeper the cut ; the greater the angle,
say 18˚, the shallower the cut .
18˚
2
11-7
0
1
2
0
1
3
1
4
2
1
52
3
6
4
7
52
3 8
6
.70
.80
.60
9
.60
.90
7
.90
.70
.80
0
.50
0
.50
.30
.30
.10
10 4
.20
.40
.40
.10
3 8 .20
9
11
10 4
12
11
5 13
12
14
15 6
5 13
14
15 6
1
2
Just as with through dovetails, the cumulative plus
and minus tolerances in the manufacturing processes of routers, bits and guidebushes, makes it
impossible to provide the exact bit depth setting
to provide a first-time precision fit. It is only by
trial and error test cuts that a fine fitting joint can
be attained. This trial-and-error testing is common
to all dovetail jigs. The good news; we provide you
with the starting depth for each bit and the ‘best fit
depth’ is measurable and recordable for all future
first-time fits, by measuring either the depth of
cut  or the bit projection .
11-8 CUTTING A TEST JOINT
You will need a router, the 7⁄ 16"[11,1mm]
guidebush, and the No.120-8, 1⁄2"[12,7mm]
14° dovetail bit. Note: the 80-8 bit cuts too deep
for 3⁄ 4"[20mm] boards (see the HB bit selection
charts on page 161).
You will also need several pieces of 3 ⁄ 4"x 5
1 ⁄ 2"[20x140mm] x 8"[200mm] or so long,
and the plastic bridge piece extrusion. Note:
Half-blind pin boards must be a minimum
½"(13mm) thickness for clamping. Thinner
boards must be packed up from the jig body;
see 11-23.
84
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
11-9
Clamp the spacer board in the rear clamp.
11-10
Mount the finger assembly on the support
brackets in the H HB TAILS mode, flat
on the spacer board, scales set on the thickness of the tail board ( 3 ⁄ 4"[20mm] in this
instance).
The H HB TAILS scale is always set at the
tail board thickness.
(The scale increments above 1-1 1⁄ 2 “[2538mm] are for use on sliding dovetails - see
chapter 16.)
11-11
1
Measure and mark a line on the inside face of
the tail board  to the working depth of the
bit to be used as per 11-2 this chapter. Clamp
this test tail board in the left front clamp,
against the side stop with the top edge flush
under the guidefingers, and the inside face
i of the drawer side away from the jig.
85
11-12
Unlock and raise the finger assembly support brackets slightly so that the finger
assembly is about 1⁄ 16"[2mm]  above the
boards. This will allow easy movement of
the guidefingers.
1
11-13
The following joint design is only a suggestion for this trial. It has a typical and traditional even layout of pins, with half-pins at
each edge. The Leigh jig, however, allows
for an infinite variety of joint designs, and
boards of different thicknesses can be joined
to each other as shown in this illustration.
Before attempting joints of asymmetrical
design, please see chapter 15.
11-14
Ignoring the extreme outer guidefinger next
to the scale (which just supports the router), loosen enough of the adjacent guides to
give the required tail layout. The half-pin
guidefinger position illustrated will give a
half-pin socket profile like that shown (dotted lines).
86
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
11-15
If the gaps between the guidefinger tails are
wider than about 1⁄ 8"[3mm], mark off and
cut some pieces of bridge extrusion  to fit
into the slots in the ends of the guidefinger
tails. Be sure to make them slightly shorter
than the distance between the guidefinger
shoulders , so the guidefingers will not
be forced apart when you put in the bridge
pieces. Squeeze the open side of the pieces
and push into place. They are a friction fit.
After completing a project, save the bridge pieces
for future use.
1
2
2
11-16
1
2
3
4
1
2
1
4
Remember to tighten any loose guidefingers.
Lower the finger assembly back onto the
spacer board and workpiece. It must touch
the workpiece or the depth of cut will vary
and the joint won’t fit. The scale should be
set on the tailboard thickness, in this case
3⁄ 4"[20mm].
25 –38
20
15
10
5
11-17
Attach the 7⁄ 16"[11,1mm] guidebush to the
router securely.
87
11-18
Mount the supplied No.120-8 bit to the
router.
11-19
Remember to follow all safety precautions
when routing.
11-20
1
2

Adjust the bit height until the bit tip is level
with the marked line . For the first light
cut move the router from right to left. Make
sure you control it firmly, because it is driven
in this direction by the bit. Only the tip of
the bit should be cutting on the first cut
. This back or climb routing leaves a very
clean shoulder in side grain.
88
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
11-21
Now rout in and out from left to right following the guides and bridge pieces to rout
out the pin sockets, leaving the tails.
See 17-10 Hints and Tips
11-22
Remove the test tail board, then clamp a scrap
board in the front of the jig so that the top
edge projects above the top face of the jig by
about 1⁄ 8"[3mm]. This will keep the scrap
piece below the path of the bit when routing
the pin board.
Remove the spacer board from the rear
clamp.
1
11-23 If you're mounting Thin Pin Boards:
2
1
The minimum recommended pin board
thickness is 1⁄ 2"[13mm]. If you wish to rout
a pin board less than the minimum thickness , it will be necessary to pack the board
up from the jig body. We suggest using a
piece of 1⁄ 4" to 3⁄ 8"[6 to 9mm] plywood for
this purpose .
89
11-24
Place a test pin board in the left rear clamp
against the side stop, fitting its front end edge
flush against the vertical scrap piece, with the
inside face i of the drawer front away from
the jig body. The pin board is now positioned
with the edge to be routed flush with the jig’s
front face, correctly registered for the scale
readings. For drawers with rabbeted fronts,
see Chapter 13.
11-25
1
4
1
2
3
4
1
2
5
10
Rotate the finger assembly to the h HB
PINS mode and set the HB PINS scale
equal to the tail board thickness (i.e., the
same setting as for the tails: in this example,
3⁄ 4"[20mm]).
Both HB pins and HB tail scales are always
set to the tail board thickness.
15
20
25 –38
11-26
Make sure the finger assembly is flush and
level on top of the pin board.
The guidefingers must be touching the pin
boards or the depth of cut will vary and cause
poor joint fit.
90
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
11-27
If you have difficulty leveling the finger
assembly on a narrow workpiece, place a
board the same thickness as the pin board
under the other end of the finger assembly,
but not in the rear clamp.
11-28

Rout out the waste between the pins. Rout
each space from left to right. Do not back
rout on end grain. If the bit enters on the
right side of the opening there will be a very
strong pull to the left, so...
11-29
Rout each opening in at least three or four
passes, left to right.
91
11-30
Remove the pin board and test the joint for
fit. If the joint is loose, as shown here, you
need to lower the bit by the same amount
as the gap at the bottom of the pins 
(when the pins are pulled against the socket
sides ). If the joint is too tight, raise the
bit slightly. Test again. You cannot rout the
same board twice with a dovetail bit, so use
two fresh board ends for each test.
1
2
90 o
11-31
0
1
2
1
3
4
5
2
40
36
.50
.90
6
8
12
7
.30
16
0
20
56 60 0
.01 4
"
.40
32 28 24
52
48
44
.80
.60
.70
.20 3
8
.10
1
9
10
4
Keep the test tail board that fits well, and
mark it with the number of the bit you used
to rout it. For quick set-up next time, clamp
this tail board in the jig as a depth-of-cut gauge
 to show how far to lower the bit. Better
yet, measure the bit projection from the end
of the guidebush  or guidebush flange 
and record this for fast set-ups in future.
3
2
11-32
≤1/64[0,3mm]
When you have the proper tightness of fit,
check the flushness. The tails should be under
flush to the pins by no more than 1⁄ 64"[0,3mm]
to allow for cleanup (exaggerated here). The
concentricity of the collet and guidebush on
different routers will affect this tolerance.
92
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
11-33
1
4
1
2
3
4
1
2
If the tails stand out from the pins, set the
h HB PINS scale away from the operator by the amount required.
5
10
15
20
25 –38
11-34
1
4
1
2
3
4
1
2
≤1/64"[0,3mm]
If the tails fit in too far past the pins ends, set
the h HB PINS scale toward the operator
by the amount required. These adjustments
for “flushness” are made only in the h
HB PINS mode.
5
10
15
20
25 –38
11-35
To make a box, rout all four ends of the tail
boards, keeping the inside face i of the tail
boards away from the jig.
93
11-36
Rout all four ends of the pin boards keeping
the inside face i of the boards away from
the jig.
Note: When making drawers you may prefer to
use through dovetails on the rear corners.
11-37 End-on-End Dovetails
While you have the router set up and the
cut depth correctly adjusted for half-blind
dovetails, it is a good time to try end-on-end
dovetails. These are made in the same modes
as half-blind joints, but the boards are both
routed vertically in the front clamp. End-onend joints may be up to 3⁄ 4"[20mm] thick.
(See Chapter 14 for end-on-end dovetail
procedures.)   ■
94
H A L F - B L I N D D O V E TA I L P R O C E D U R E S
Chapter 11
User Guide
CHAPTER 12
Quick Reference
Half-Blind Dovetails
96
QUICK REFERENCE
Chapter 12
-
H A L F - B L I N D D O V E TA I L S
User Guide
Chapter Foreword
You haven’t used the jig for a while and just
need reminding of some of the basics. Here
they are for Half-Blind Dovetails.
97
A VERY IMPORTANT REMINDER!
About Half-blind Dovetail cutter depth, and board thickness.
■
Half-Blind Dovetail bit selection is
based on the thickness of the pin
board (drawer front). Choose a bit for its cutting
depth specification. Its specified cutting depth must
always be less than the thickness of the pin board.
■
A dovetail bit used for Half-Blind Dovetails will produce only ONE SPECIFIC CUTTING DEPTH.
You can make small cutting depth adjustments
(±1⁄ 64") to achieve perfect joint fit ...but not to alter
joint design.
■
All Half-blind pins and tails must be routed with the
SAME BIT, and at the SAME DEPTH OF CUT.
■
All Half-blind dovetail bits work with the 7/16" O.D.
template guidebush supplied with your Leigh jig.
■
Only 1⁄ 2"[12,7mm] diameter bits can be used for halfblind dovetails.
If you do not understand these points, study pages 80 and 81 in Chapter 11
"Half-Blind Dovetail Procedures".
12-1
On the Leigh jig, all half-blind dovetails
are routed using a 7⁄ 16"[11,1mm] O.D.
guidebush.
98
QUICK REFERENCE
Chapter 12
-
H A L F - B L I N D D O V E TA I L S
User Guide
12-2
Half-blind dovetails are laid out in the H
HB TAILS mode with the finger assembly slightly raised above a tailboard (e.g.,
drawer side).
12-3
Half-blind ( HB ) tails: Drawer sides
(tailboards) are clamped vertically in the jig.
The inside face i of the drawer side goes away
from the jig body. The finger assembly is in
the H HB TAILS mode, set to the thickness
of the drawer side. Use bridge pieces where
required (see 11-15).
n
12-4
n
Half-blind ( HB ) pins: Drawer fronts
(pinboards) are cut with the board clamped
horizontally in the jig. The inside face i of
the drawer front faces away from the jig body.
The finger assembly is in the h HB PINS
mode, and again set on the thickness of the
drawer side (but adjusted for a flush fit, see
11-32 to 11-34).   ■
CHAPTER 13
Rabbeted
Half-Blind Dovetails
100
R A B B E T E D H A L F - B L I N D D O V E TA I L S
Chapter 13
User Guide
Chapter Foreword
Before attempting rabbeted half-blind
dovetails, first master the techniques of
flush half-blind dovetails in the previous
chapter.
101
11-1
Î
È
Rabbeted Half-blind Dovetails:
 Pins h
 Pin sockets
 Half-pins
 Half-pin sockets
 Tails H
 Tail Sockets
The pins fit in the pin sockets. Joints should almost
always end each side with
half-pins.
£
{
x
£
11-2
Ó
£
Î
Minimum Rabbet
Depth
7/16" [11,1]
Cutting
Depth
3/8" [9,5]
Dovetail
Bit No.
No.128-8
1/2" [12,7]
7/16" [11,1]
No.120-8
9/16" [14,3]
1/2" [12,7]
No.112-8
11/16" [17,5]
5/8" [15,9]
No.101-8
13/16" [20,7]
3/4" [11,1]
No.80-8
Numbers in brackets are millimetres
Guidebush
Diameter
7/16" [11,1]
Rabbet depth  determines
the maximum depth of cut ➁
you can use. Select a bit with a
specified cutting depth that is
1⁄ 16"[1,6mm]less than the rabbet
depth. Only 1⁄ 2"[12,7mm]➂
diameter bits can be used for halfblind dovetails.
Use this chart to select a Halfblind Dovetail bit to suit your
rabbet depth. For full bit
specifications see Appendix II.
102
R A B B E T E D H A L F - B L I N D D O V E TA I L S
Chapter 13
User Guide
13-1
Provided the drawer front lip is 3⁄ 8"[9,5mm]
or less in thickness , you can mount and
rout rabbeted drawer fronts and sides
exactly the same way as flush drawer fronts,
except...
£
13-2 Rabbeted Pins
You will need to clamp a scrap stop block  in
the front of the jig out from the jig’s front face by
exactly the depth of the rabbet ➁.This brings
the pin ends exactly in line with the front
jig face ➂, ensuring that the scale reading
is accurate.
r
Î
r
Ó
£
13-3
£
An easy accurate way to do this is to rabbet the
end of a scrap piece  vertically over a dado
blade or router bit at the same time as you
rabbet the drawer front (horizontally) .
£
Ó
Ó
103
13-4
If the rabbet is greater than 3⁄ 8" in thickness,
the drawer side must be blocked away from
the front side stop by exactly the depth of the
rabbet. So make up a block  and...
£
13-5
Stick the block  to the jig face with doublesided tape, making sure it touches the side
stop.
£
13-6
The drawer side will now be stepped in
from the side stop by the width of the
rabbet, bringing the sockets in line with
the pins.
104
R A B B E T E D H A L F - B L I N D D O V E TA I L S
Chapter 13
User Guide
13-7
Make sure you select a dovetail bit that has a
working depth of cut less than the rabbet height.
Otherwise, you will rout into the rabbet.
13-8
It is difficult to clean up the drawer sides
and front corner after assembling a rabbeted drawer, so make sure the fit is flush
before you complete the drawers (see 11-31
to 11-33).   ■