b - MILLING A SLOT
Now here's the part I like. Just walk over to your milling
machine and put the acoustic guitar jig in the vise.
"Say what?"
Oh. Hmmm. Well, can I suggest that you CONSIDER buying
one? There's no end to the utility of a milling machine in any
small shop, especially a repair/builder's shop.
Even the smallest vertical milling machine will bring your
shop's capabilities to a whole new level. Anything that's sup-
posed to be drilled, bored, pocketed, trued, parallel, flat,
square, slotted, threaded, round, tapered, grooved, funked up,
chamfered, sliced, diced, etc., etc. will stand a good chance of
getting that way if you can affix it to the table of your vertical
mill.
I'm well past the point of running my shop or doing my work
without one and I consider it the most important and versatile
tool in my shop.
For this job a sturdy, thick work board with a strong tab for
gripping in the milling vise will serve to support and position
the guitar. Clamp up and indicate the slot true with the
machine travel, insert the bridge jack and tension it, squirt
some air at the cutter and make a pretty slot. The great advan-
tages of the milling machine over the router include:
1. Absolute confidence in control of the cut.
2. The ability to widen, deepen or lengthen the slot in tiny
increments, as needed.
3. Perfect visibility.
4. Control over the angle of the saddle slot (5-8 degrees) as
desired by simply tilting the jig in the vice.
5. Great setup for drilling a clean and accurately positioned
wire hole.
SADDLES
Another great advantage of the mill is the beautiful saddle
blanks it can generate. Whatever your choice of saddle mater-
ial - organic or plastics, the blank will come out square,
straight and parallel - and to size.
Actually, I like to leave just a couple thousandths for sanding
with 500 grit. This makes possible a really sweet fit between
slot and saddle so that the saddle can just slip in and out with-
out friction, but not looser. For example, the saddle should
slide into the slot easily, but not fall out of the slot when over-
turned. This transfers energy from string to bridge optimally.
Even if you make saddles by hand or on a belt sander you
should try for this kind of fit.
Use a micrometer to check thickness all over the blank and
really get it parallel and square. If you err on the tight side and
the pickup response is weak or muffled, it's a quick job to sand
another thousandth off. Too loose, and it's junk. Be sure to
check for flatness and squareness on the bottom of the saddle
again before installing it. There is often a distortion when part-
ing the blank off a larger piece or removing thickness. Also,
LIGHTLY chamfer the bottom corners all around.
TROUBLESHOOTING
1. WEAK STRING OR STRINGS
Try pushing down on the saddle over the weak strings.
Sometimes it just needs a little persuasion when first strung
up. (Tell your customer this.) If this doesn't help, and repeated
pushing yields repeated groans, crackles, etc. (amp on please)
then you can be sure that the pickup is not getting the even
squeeze it needs to get. Remove the saddle, check the bottom
for flatness and squareness, and check for debris in the slot.
Next, sculpt the saddle to equalize pressure on the pickup.
This will only rarely be necessary if you've done a careful job
of jacking the guitar top.
By sculpting, I mean the adjustment of the saddle bottom to
form, under string tension, a surface parallel to the slot bot-
tom. This is done to even out the pressure on the piezo ele-
ments. For example, if the outside strings are low in
output,scrape the saddle hollow to increase pressure on the
outside elements. If you've recut the slot with a bridge jack, as
suggested, and you encounter this problem, it probably means
that the jack should have been adjusted taller.
You may also try placing a .020" cedar shim under the entire
length of the pickup. A cedar shim often will have just enough
"give" to correct string balance problems that result from
minute differences between the saddle and the bridge slot.
2. PIEZO-DECEPTION
Sometimes a string's "low" output can be relative to an
unnaturally "hot" adjacent string which is too lightly loaded.
This can be hard to troubleshoot until you know that an ele-
ment's output when properly loaded is LESS than its output
when loaded too lightly.
Demonstrate this for yourself by loosening and then tighten-
ing all the strings while the guitar is plugged in. You will notice
an increase in output and a change in tone.
With a ceramic pickup, you can usually hear some output
from a string even if the element below it is totally unloaded,
due to "leakage" from adjacent elements. In this case, applying
thumb pressure over the problem string will usually activate
that element and make those crunch and crackle noises. If so,
it's time to check and correct straightness, squareness and fit
again.
A common example of this that can be very puzzling can
occur in guitars with lots of "belly up". In the event that the
bridge slot is being crowned up by bridge tension, the outer
strings might EITHER be too hot or too low depending on
whether they are loaded, respectively, too lightly or not at all.
3. 60 CYCLE HUM
If this is a problem and is accompanied by low output, it is
almost certain to be the result of very little pressure on the
pickup, yielding a poor signal to noise ratio. One common
cause is a saddle that's binding in the slot. Be sure not to get
too carried away when easing the fit between saddle and slot.
Try for the closest slip fit that you can achieve.
UNDER SADDLE PICKUP INSTALLATION ... Continued
