3. Under string tension, lay a straightedge across the top
behind the bridge. Measure the "belly up" of the top at the
edges. This measurement will allow you to reproduce the
efforts of string tension by placing a padded screw jack
(Fig. 3) inside the instrument under the bridge plate and
jacking the top up to this measurement. This step will help
to ensure a flat bottomed slot when the guitar is strung up,
as well as supporting the top and reducing flutter and
excitement (yours and the guitar's) during machining.
Figure 3 - JACK-Internal jack used to prevent
movement of top during critical routing of saddle
slot prior to pickup installation.
4. No end mill or router bit is capable of cutting a slot width
identical to its diameter. All rotary cutters will shake,
bounce on their own chips, etc. and produce a slightly wider
slot. One way to beat this is to send a set of bits to your
local cutter grinding shop. For a couple of dollars they will
reduce the diameter of your standard 1/8" and 3/32" cutters
by about .010". These reduced cutters can be used first and
followed by full size bits to kiss off the final few thou-
sandths, resulting in a beautiful "wall" surface that will be
very close to being "on size". In lieu of a reduced cutter, I
like to use a 7/64" (.109") two flute spiral end mill.
5. Single flute bits will perform best in a router. There's lots of
chip clearance, lots of positive rake to cut cleanly, and less
tendency to bounce around in the slot full of chips.
6. Speaking of chips, the best cut will be had by directing
compressed air right at the bit to keep the slot clear and
the but cutting freely.
7. We recommend Ekstrom-Carlson bits, available from your
local E-C distributor (call 815-968-0961).
3/32" x 9/32" long x 1/4" shank PART # 011-0309
1/8" X 3/8" long x 1/4" shank PART # 011-0412
(Also their two flute downcutting bits are unsurpassed for
general {chipping free} routing chores in the shop.)
8. 5 - 8 DEGREES: What about these few degrees? Well, we
think you should tilt the saddle back by this amount when-
ever you cut a saddle slot. Here's why:
a. The backwards tilting saddle will be much better at resist-
ing the tendency of the center strings to bow to the saddle for-
ward and create a long "D" shaped saddle slot and its accom-
panying space between the back of the saddle and the back of
the slot.
b. The pickup will "see" more downbearing force and will
sound better.
c. As a result of better force distribution between the saddle
and bridge, the bridge will remain more stable, resist distortion
and bending, and sound more solid. (Remember Objective II?)
Even though it's more trouble and it ain't historic, etc., we're
convinced that it does really improve the pickup installation
and often, the acoustic response. Further, it's not so much
angle that it looks objectionable.
As a bonus, this technique often helps us move the string
take off point a little further back on the bridge, when needed
to help correct "folding-up-sharp" intonation.
a - ROUTING A SLOT
You will need a small plunge router to do the job. Make a
base for the router with a 5-8° angle to achieve an angled slot.
Make a routing jig to fit on top of the guitar. Cover the bottom
of the jig with a cork or rubber gasket. The jig bottom should
clamp to the guitar's edges only, and not tend to squeeze out
the belly shape in the top, thus accommodate the aforemen-
tioned screw jack. The guide for the router base must fit pre-
cisely to avoid slop in the cut. Make adjustable endstops for to
the length of the cut.
A nice way to locate the existing slot is with an undersize
pin chucked in the router. Dropped in the slot, the pin is a
quick set up tool for slot angle and ends. (Fig. 4)
FIQURE 4 - PIN LOCATES SLOT
WITHOUT RISK OF DAMAGE.
UNDER SADDLE PICKUP INSTALLATION ... Continued
1/4" diameter shank for use
in standard router chuck
Turned smooth
to .090" diameter
Top swivels and tilts
(ideally a ball joint)
to match interior angle
of guitar top.
Knurled collar to adjust
vertical height of jack.
Notched to clear back
reinforcing strip.
Threaded to allow
vertical adjustment.
