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 proc= ess I use to

-saw out the parts, fair the edges<= o:p>

-precisely mark and drill the holes= in the neck

-attach the knee block

Lumber selection<= o:p>

With larger harps and higher tensio= ns, lumber selection becomes more critical. The pillar must be able to r= esist 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 l= bs 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 st= rong as Cherry.

Strength and hardness of several speci= es used for the neck and pillar

	Density	Stiffness	Hardness	Strength
Cocobolo=	1=			10,067
Wenge	0.87	2.46	1,630	19,500
Bubinga<= /span>	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<= /o:p>	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<= /o:p>	0.48	1.45	850	10,700

Density =3D Specific Gravity &= nbsp;

Stiffness =3D Modulus of elasticity, Million lbf/square inch &n= bsp;

Hardness =3D Side Hardness, lbf &= nbsp;

Strength =3D Rupture Bending Streng= th, psi &nbs= p;

Sourced from Chapter Four of the US Forest Products Laboratory Wood Han= dbook and http://woodworkerssource.net/onlinewoods/<= span style=3D'mso-tab-count:1'> =

The local DIY home center sells map= le, 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 hand= book (available for free on the internet). Don’t be bashful= about asking questions. If th= ey 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 o= f the instrument.

I live near = Washington D.C.<= /st1:place> and am fortunate to have a number of well stocked lumberyards within a two = hour drive. The best ones wi= ll stock 40-50 types of wood, rough sawn in 4/4, 6/4 and 8/4 thicknesses.

L= umbering Semantic

I= n North America, “8/4” is a nominal size = for lumber. Logs are cut into pla= nks 2” thick. After the pla= nk has dried and been planed smooth, it will be 1.5-1.7 inches thick. Smaller harps can be made fr= om 6/4 stock. If the harp is g= oing 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 t= hree layers of thinner stock to get the thickness specified in the design.

Three Ways to Reinforce the Neck

When necks break, the fracture usua= lly 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. =

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The neck is in tensi= on 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 spl= ine usually extends up into the area where the bridge pin holes are to be drill= ed, 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 splin= es, I crank the blade on the table saw so it extends 1½” above the table. I set the rip fenced o= n 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 i= nch 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 slid= e 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 sl= ots on a table saw. Splines can b= e 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 pat= ch

This is usual= ly 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.<= span style=3D'mso-spacerun:yes'> I cut a strip that is as wid= e as the neck, and long enough to cover the short grain running out – usua= lly 6-12”.

I mix a small batch of epoxy (15-30ml), and paint the wood with epoxy then apply the Carb= on fiber. I spread just enough e= poxy 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 tap= e, 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 inconsp= icuous place, and no one noticed it unless I pointed it out, so I rarely try to co= ver it up now. =

The bottom of a nec= k that has been reinforced with a Ca= rbon Fiber patch.

After about 2= -3 hours the epoxy will gel, and I remove the masking tape from the sides of t= he neck. After the epoxy has cur= ed for 8 hours or more I will scrape the patch so it is smooth, rounding the corne= rs.

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 collec= tion 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 f= iber on solid timber because it is quicker and looks better to me without the gl= ue lines.

Another alternative is to use piano= pin block or die makers plywood for the neck.&= nbsp; 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.<= span style=3D'mso-spacerun:yes'> As I cut that line on = the band saw, I pay close attention to each line and how accurately it needs to= be cut:

<= /o:p>

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

Bottom of the neck – stay outside the line to ensure you will have space to mount the le= vers

Sides of the pillar, top of Neck should be smooth fair curves (SC) - I focus on making a cut that does not h= ave 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. &= nbsp;

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 bo= x, 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 w= orked well enough, but I was not able to replicate the clean precision I saw on many commercially made harps. Conv= inced the makers were using a special bit, I asked Mark Hillman, a finicky machin= ist and bagpiper maker what he thought they could be using. He explained that many amate= urs 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 abou= t to pass through the other side of the neck, it will burst through, tearing lar= ge splinters from the edges of the hole.

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

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

During the first plunge, the bit do= es not have to lift the chips too far out of the hole. Subsequent plunges have to be shorter. Really hard woods ma= y 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 plung= e 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 u= sing the proper sized bit and drilling or reaming to the proper depth.

First, I drill the holes for the br= idge pins. I set the depth s= top 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.

The final bridge pi= n height can be set with a block to wo= rk with the harp levers. Depending on the hardness of the wood, the tuning pin will move up t= o 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 te= nd to ream just enough to allow the strings to wrap nicely below the hole, lea= ving room for wear down the road. =

Next, I drill the holes for the tun= ing 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” th= ick . Before I ream the holes, I = flip the neck over. If y= ou find yourself reaming a neck on the same side that you can see the bridge p= ins, you have made a mistake. I re= am 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 us= ually cycle the reamer two or three times into the same hole. Reaming goes a lot faster th= an 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 str= ings and nylon strings that are gr= eater than .050 in diameter. Again, I set the depth stop on the drill press so the tip of the rea= mer barely penetrates the neck.

Attach the Knee Block

Most harps have some kind of knee b= lock 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 repa= ir one or two knee blocks that had popped off when the harp was dropped or ban= ged, so I usually reinforce this joint using one of two methods. You can reinforce the joint with t= wo 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 loca= tion 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 under= side 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.

<= /o:p>

Placement of the dowels to reinforce the knee block

Go on to Chapter 9<= /o:p>

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