Chapter
Eight

Fabricating
the Neck and Pillar

This chapter will discuss lumber
selection and various methods for reinforcing the necks.   Then I will outline the process I
use to

-saw out the parts, fair the edges

-precisely mark and drill the holes in
the neck

-attach the knee block

Lumber selection

With larger harps and higher tensions,
lumber selection becomes more critical.   The pillar must be able to resist
the torque of the strings twisting the neck.   The Neck will be cut into a curve and
peppered with holes for the tuning and bridge pins and cannot crack under
load.

If the harp has more than 800-900 lbs
of tension I will be choosier about the wood I use to ensure the longevity of
the instrument.   I like to
make the neck and pillar from a wood that is at least as hard, stiff and strong
as Cherry.

Strength and hardness of several species
used for the neck and pillar

Density

Stiffness

Hardness

Strength

Cocobolo

1

10,067

Wenge

0.87

2.46

1,630

19,500

Bubinga

0.71

2.48

2,690

22,293

White Oak

0.68

1.78

1,360

15,200

Sugar maple

0.63

1.83

1,450

15,800

True Mahogany

0.59

1.5

800

11,500

Black Walnut

0.55

1.68

1,010

14,600

Black Cherry

0.5

1.49

950

13,250

Bigleaf Maple

0.48

1.45

850

10,700

Density = Specific Gravity

Stiffness = Modulus of elasticity,
Million lbf/square inch

Hardness = Side Hardness, lbf

Strength = Rupture Bending Strength,
psi

Sourced from Chapter Four of the US Forest Products Laboratory Wood Handbook
and http://woodworkerssource.net/onlinewoods/

The local DIY home center sells maple,
but it is commonly a soft red maple.
It is not as suitable as Sugar maple or the other hard maples.   When you go to purchase wood, you
may want to bring a copy of the tables from chapter 4 from the Wood handbook
(available for free on the internet).    Don’t be bashful about
asking questions.   If they
can’t answer them, the wood may be a softer inferior species.

I will build harps from Mahogany or
Walnut if the client requests it, but modifications have to be made to the
design - thicker parts, reinforcing around pin holes.  I still fret about the longevity of the
instrument.

I live near Washington D.C.
and am fortunate to have a number of well stocked lumberyards within a two hour
drive.   The best ones will
stock 40-50 types of wood, rough sawn in 4/4, 6/4 and 8/4 thicknesses.

Lumbering
Semantic

In North America, “8/4” is a nominal size for
lumber.  Logs are cut into planks
2” thick.  After the plank has
dried and been planed smooth, it will be 1.5-1.7 inches thick.   Smaller harps can be made from 6/4
stock.   If the harp is going
to be more than 30 strings I get 8/4 stock.

The width of the plank required will
depend on the design, and I will often take a plywood template of the neck and
pillar to allow me to arrange parts on the plank.

If you have
trouble finding the right kind of lumber, you may have to laminate two or three
layers of thinner stock to get the thickness specified in the design.

Three Ways to Reinforce the Neck

When necks break, the fracture usually
starts on the underside of the neck near the treble end.   I have found three effective
strategies to prevent the neck from breaking.  If the harp has a strong harmonic curve,
or more than 400-500 lbs of tension, I use one or more of these techniques to
preserve its integrity.

The neck is in tension along
the bottom, the neck is usually narrow at the

treble end, and cracks start there on the
short grain, usually near a pin or screw hole.

Reinforcing with Splines

Slots
can be cut into the underside of the neck, using a router or table saw and
splines are glued into place.
This effectively turns the underside of the neck into plywood which
prevents the stress crack from forming there.   Because the slot for the spline
usually extends up into the area where the bridge pin holes are to be drilled,
I usually put the splines into place after the blank is cut out, but before the
pin holes are drilled if the knee block is attached.

To cut the first slot for the splines,
I crank the blade on the table saw so it extends 1½” above the
table.  I set the rip fenced on the
table saw so it is ¼“ from the blade and run the neck along the
fence, stopping short of the knee front corner.   I shift the fence about an inch
over and cut the second slot.

I
cut the splines out of hard maple with a zero clearance insert on the blade and
the grain of the spline runs along its length.    The spline should slide in
easily but not be too loose.  One
end of both splines is cut to an arc that matches the slot made by the
blade.    I slather the
splines and slots with epoxy and push them into place.

Necks with a strong curve or arch at
the treble end for the player’s thumb will preclude cutting spline slots
on a table saw.  Splines can be cut
with a router bit and slot cutter, but it is more tedious to fabricate the
spline and most slot cutters will only cut ½” deep.

Reinforcing with a Carbon Fiber patch

This is usually
done after the neck and pillar have been glued together, and they have been
fitted to the sound box.   I
clamp the neck and pillar upside down in a vice, and cover the sides of the
neck with masking tape which makes epoxy clean up easier.   Carbon fiber usually comes in
rolls that are 6” wide.  I
prefer unidirectional tape, but have not had any failures with woven tape.   I cut a strip that is as wide as
the neck, and long enough to cover the short grain running out – usually
6-12”.

I mix a small
batch of epoxy (15-30ml), and paint the wood with epoxy then apply the Carbon
fiber.  I spread just enough epoxy
on top of the patch to ensure that the patch is wetted out.   Two tips to make it a neater job
;  Excess epoxy can puddle and
creates a more uneven surface, so remove excess pools.  Second, the less I  mess with the cut edges of the tape, the
neater the job will be.

At one time I
covered carbon fiber with a piece of veneer to hide it.   I found the   patch is in a pretty inconspicuous
place, and no one noticed it unless I pointed it out, so I rarely try to cover
it up now.

The bottom of a neck that
has been  reinforced with a Carbon
Fiber patch.

After about 2-3
hours the epoxy will gel, and I remove the masking tape from the sides of the
neck.  After the epoxy has cured for
8 hours or more I will scrape the patch so it is smooth, rounding the corners.

Laminate the neck

Most builders recommend skewing the
grain from one layer to the next by at least 15 degrees.  Even when I used a sizeable collection
of wood hand screws and C clamps, it proved surprisingly difficult to keep
everything aligned and to generate nice tight glue line across the entire
surface of the neck.  I built five
or six harps with triple laminated necks, and none them have required
subsequent repair work.

I prefer to use splines or carbon fiber
on solid timber because it is quicker and looks better to me without the glue
lines.

Another alternative is to use piano pin
block or die makers plywood for the neck.
Do not use fir core plywood.
I tried this on three harps and each eventually split along the soft fir
core.  I’ve seen some
Paraguayan harps made from birch aircraft ply (with thin, 1mm laminations), but
these harps were strung lightly with only 700-800 lbs of tension.

Saw Out the Parts, Fair the Edges

I mark the outline of the neck and
pillar from full sized plywood or paper templates clamped onto the lumber.    As I cut that line on the
band saw, I pay close attention to each line and how accurately it needs to be
cut:

Joining surfaces
(JS) mate the neck, pillar and sound box to each other and need to be cut
accurately – go slow.

Bottom of the neck
– stay outside the line to ensure you will have space to mount the levers

Sides of the pillar, top of Neck
should be smooth fair curves (SC) - I focus on making a cut that does not have
unnecessary bumps or wavering.

After the pillar and neck have been cut
to shape, I smooth the outside curves with a hand plane.  The inside curves are trickier.  I can usually do the pillar with a short
smoothing plane at a skew angle, but the sharper curves on the neck are done
with a spokeshave or sanding drums.

Areas NOT so smooth - I refrain from
smoothing the joining surfaces till it is time to assemble the parts
together.   These need to stay
accurate, square and true.   If
the neck and pillar are to be fitted to a stave back or round back sound box, I
don’t smooth the area near the knee block.  This will be ground to shape then
they  are fitted to the sound box.

Precisely
Mark and Drill the Holes in the Neck

One of the hallmarks of a well built
harp is the two rows of precisely placed pins in the neck.    My first three harps worked well
enough, but I was not able to replicate the clean precision I saw on many
commercially made harps.  Convinced
the makers were using a special bit, I asked Mark Hillman, a finicky machinist
and bagpiper maker what he thought they could be using.   He explained that many amateurs
cannot drill straight holes because they overload the bit, especially in the
hard woods frequently used for harp necks.

As the operator pulls the hand feed
lever down and the bit enters the stock, a dome of compression forms around the
drill tip, increasing the likelihood that the bit will bend and wander.   If an overloaded bit is about to
pass through the other side of the neck, it will burst through, tearing large
splinters from the edges of the hole.

Most harp builders strongly recommend a
drill press, mainly to ensure the holes are perpendicular.   Two other advantages are equally
important.   A drill press
provides precise depth control and controlled feed rates.  A careful operator will prevent the bit
from becoming overloaded, frequently lifting the drill bit or reamer out to
clear the chips.  The result is a
clean straight hole.   My
fourth harp neck looked as clean as any commercially made harp.    Here is how I do it:

Drill the hole in a series
of plunges clearing the chips from the flutes each time.

During the first plunge, the bit does
not have to lift the chips too far out of the hole.  Subsequent plunges have to be
shorter.  Really hard woods may take
5 plunge/retract cycles.  The key is
to realize when the chips are no longer being lifted from the tip of the
bit.   If the final plunge is
only removing the last few millimeters of wood, you will not get much tear
out.

It takes me about two hours to drill
the holes for the bridge pins and tuning pins for a five octave harp.    It is helpful to have the
tuning and bridge pins you will be using in hand.  That way you can be sure you are using
the proper sized bit and drilling or reaming to the proper depth.

First, I drill the holes for the bridge
pins.   I set the depth stop so
that ¼“of the bridge pin head will remain above the surface of the
neck.  I find I can get a nice clean
hole (with no tear out) if I drop the bit very slowly into the work for
the first 1/8” or so.

<pic showing neck with bridge pins
and tuning pins inserted>

The final bridge pin height
can be set  with a block to work
with the harp levers.
Depending on the hardness of the wood, the tuning pin will move up to  ¼“ deeper as the harp is
brought up to tension.   As the
hole wears over the years, the pin will move farther into the hole, so I tend
to ream just enough to allow the strings to wrap nicely below the hole, leaving
room for wear down the road.

Next, I drill the holes for the tuning
pins through the neck using a 3/16” bit.    Each hole may take 3-5
plunge/retract cycles on a full sized harp neck that is 1¾” thick
.  Before I ream the holes, I flip
the neck over.   If you
find yourself reaming a neck on the same side that you can see the bridge pins,
you have made a mistake.  I ream all
the holes with a #4 reamer, setting the depth stop so the tip of the reamer
barely penetrates the neck.
Here too, you want to watch to make sure that you are not jamming the
flutes full of shavings.  I usually
cycle the reamer two or three times into the same hole.   Reaming goes a lot faster than
drilling the initial hole because I don’t have to stop the spindle to
clear flutes clogged with shavings.
Finally, I ream the holes on the bass end with the larger #5
reamer.   I usually use  a #5 reamer with any wire core strings
and nylon strings that  are greater
than .050 in diameter.
Again, I set the depth stop on the drill press so the tip of the reamer
barely penetrates the neck.

Attach the Knee Block

Most harps have some kind of knee block
that helps resist the torque of the strings.  These are usually glued into place after
all the holes have been drilled in the neck for the pins.    Most of the carving and
shaping is done before the block is permanently attached.

I had to repair
one or two knee blocks that had popped off when the harp was dropped or banged,
so I usually reinforce this joint using one of two methods.  You can reinforce the joint with two
3/8“ dowels in the joint.  If
the harp is a round back, the dowel on the back of the joint (nearer the
player) is cut shorter.   I
usually make a blind dowel joint (one where the dowel will not show once the
neck and knee block are glued together) using centerpoints to mark the location
for the holes to be drilled in the second piece of wood.        The
other method is to laminate a fiberglass or carbon fiber patch on the underside
of the neck after it has been trimmed to fit the top of the sound box.  It is quicker to do than the blind
dowels and can be done concurrently with reinforcement on the underside of the
neck.

Placement of the dowels to reinforce
the knee block

Copyright ©
2007, Rick Kemper

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