Chapter Seven

Attach= ing the soundboard

The sound board is under a lot of strain, and if you are building a light and responsive board, it will eventually rupture or start to come off. The goal is to forestall that failure for 15-30 years. A broken soundboard is not the end of the world, but replacement ent= ails about half the work of building a harp from scratch, so I take some pains w= ith this part of the building process.

Many modern builders rely solely on glue to hold their soundboard to the shell. This allows them to create a= very slick modern look and eliminates the labor required for adding edge battens= and mechanical fasteners.

This chapter will describe how to <= o:p>

-prepare the face of the sound box<= o:p>

-glue the board into place

-apply mechanical fasteners and edge treatments to secure the board

This approach presumes the foot of = the pillar will be attached to the string band with a lag bolt (a popular configuration for many folk harp designs). Other designs terminate the = pillar onto the base of the sound box, and this approach may require additional reinforcement to transfer the strain from the foot of the pillar back to the string ribs which are pulling down on the strings.

Cross sectional view showing three ways to attach the foot of the pillar to the sound box

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Bolted Foot, Pocket hole in Soundboard= , Tie Block.

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The pocket hole is u= sually used with a plywood sound board. &nbs= p; A hole for the foot of the pillar is cut into the board, and the bot= tom of the board is nailed and glued to the base board. In a tie block termination, a chunk of wood is screwed to the bass and the string ribs. Variations on the tie = block will use a metal strap or Fiberglass reinforcement in lieu of the wooden bl= ock.

Most string ribs are centered at th= e bass end, and in the bolted foot design, pass underneath the pillar. I cut a channel at the top a= nd bottom end of the sound box for the inner string rib.

Before I cut the channel for the top end, I play around a bit with the lateral alignment of the string rib at the treble end. Most builders strive to make the s= trings drop vertically down from the neck to the center of the string rib. The strings can angle in fro= m the bridge pin, but if the angle is too sharp, it will be difficult to fit shar= ping levers or the string may slip off the notch on the bridge pin. Some builders are fastidious= about centering the string holes down the center of the board, and if this is the look you are striving for, you will need to position the neck accordingly.<= span style=3D'mso-spacerun:yes'> The alternative is to offset= the string rib to one side, which is done by number of harp builders and does n= ot seem to dramatically affect the instrument’s tone. The offset will depend= on the width at the top of the sound box and the thickness of the neck.

I place the soundboard on the sound= box where I want it, and mark the edges of the inner string rib on the sound bo= x at the bass and treble end. I re= move the sound board and use a square to extend those marks across the cap and base. With a handsaw, I cut a= kerf on top of the line to the approximate depth of the rib. Then use a router set to the right= depth to clean out the waste between the kerfs.

After checking the fit of the inner= rib in the notches, I trace the inner and outer edges of the sound box onto the sound board. This will help determine where glue is spread later. At this point, it is customary for the maker to sign and date the soundboard where it can be read through the bottom sound hole.

Harp builders have used a variety of glues for attaching the soundboard. &= nbsp; And after loosing a board or two, most builders have some pretty str= ong opinions as to which glue is most appropriate for this critical joint. I suspect some of these prej= udices have more to do with the builder’s familiarity with a specific adhesi= ve, their work habits and available clampage. See the appendix for a more complete discussion of glue choices.

If you cannot get a nice tight fit between your shell and the sound box, or if you cannot provide even, adequa= te clamping pressure, I would suggest you use epoxy because it can tolerate gaps and do= es not require much clamping pressure.

Before you mix your epoxy, select a clamping method and do a dry run so you have a good idea of how much time y= ou have before the adhesive sets.

I use about 60ml of epoxy to attach= the sound board for a 36 string harp. &nb= sp; I

Carefully measure the epoxy to the specified ratio and thoroughly mix the epoxy for a full minute, scraping al= ong the sides and bottom of the mixing cup. Then I use a cheap flux brus= h (50 cents) to spread the un-thickened epoxy along the face of the sound box and between the pencil lines on the sound board.

I mix fine sanding dust (wood flour) with the balance of the epoxy to make a paste the consistency of catsup. This is spread with the mixing sti= ck along the top edge of the sound box.

It is fairly easy to clamp a soundb= oard to a square back harp. Stave = backs and round backs prove to be more of a challenge. Some builders solve this by = using mechanical fasteners as clamping devices. The redundancy provides a ba= ckup system if and when the glue loses its integrity (a belt and suspenders approach). <= /span>

The simplest approach is to use a pneumatic stapler with ½ inch staples = to staple the soundboard down. Care must be taken to ensure the force of the driving head does not = push the staples through the thin, soft wood at the treble end of the soundboard= . Most builders set the pressu= re fairly low then go back with a hammer and punch to level any staples standi= ng proud. Later the fasten= ings may be covered with a decorative lamination of some kind.=

Sprung Soundb= oard Clamping Frame

I developed a jig with two curved be= ams that allow me to clamp the sound board&nbs= p; to the sound box using one clamp at each end. It works well with epoxy for= stave backs and round backs, and allows ample access to remove excess glue inside= the sound box through the sound holes.

Two curved 1x2̵= 7;s are used to distribute clamping pressure from the ends of the jig along their length= to the edges of the soundboard. The curve is set by bending the 1x2 over a ½” block whi= le clamping each end to a sturdy work bench. A line is scribed along the = board a half inch above the bench top. &nbs= p; Each 1x2 is then trimmed to the line.

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The two curved 1x3 boards are screw= ed to 2x2 blocks so that they are held apart at the widths of the treble and b= ass end of the sound box. <= o:p>

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Clamping the soundb= oard – the jig is placed on scrap 2x4’s, and the soundboard position= ed on top of that. Spread the ad= hesive on the edges of the shell and place clamps at each end (indicated by arrows= in the last panel). It is usually necessary to screw a temporary block on the base plate to give the clamp purchase.

Dressing up the Sound Board Edge

There are a variety of treatments t= hat can be used to dress up the joint between the sound box and sound board. I will describe the basic ap= proach for my favorites here.

Cross Section - Veneering the Sides

Steve Green used to make kit harps, and he had the builder laminate the entire si= de of the harp after the back and sound board had been glued into place. I built a few of these kits = for clients. First the veneer is cut so it is ¼ - ½ inch wider than the side. Next a thin but uniform laye= r of yellow glue is spread on the side of the harp. Then, the veneer is cl= amped into place using a layer of carpet padding between the veneer and a ¾” board (backing caul). The carpet padding helps distribute the pressure evenly over the veneer. After the glue dries, the ex= cess veneer is trimmed flush.

Cross section of Square back box with thinner sides, liners and applied bindings

Bindings

A fancier method is to use a binding. Most guitars use a decorative binding to cover the end grain and any gaps left by less-than perfect seam between the sides and top of the instrument.

There are fancy varitions of this t= hat use layers of contrasting veneer between the binding and sound box.

To put bindings on a harp, I rout a small rabbet (approximately ¼” wide and .125-.1875” deep) along the edge. Next, I cut a= strip of solid stock on the table saw. I cut it so it is 1/32” wider and thicker than the rabbet. I glue the strip into = the rabbet, securing the binding every 2-3” with masking tape. After the glue has dried, the bind= ing and excess glue can be scraped or sanded flush. Because the edge of the inst= rument is subject to a lot of dents and dings, the bindings are usually made from a hard, dense wood. You can make your own, or get fancier bindings with fancy inlays strips from guitar/Luthier suppliers like Stewart MacDonald.

The most secure method for reinforc= ing the sound board/shell joint is to use a screwed batten. The batten is secured every two in= ches with countersunk screw into the liner and shell. The top of the batten is covered w= ith veneer or an edge banding. This is a little more labor intensive than the other methods, but is cheap insurance against a blown board.

Cross section of a batten inlay edging= and Jack Yule’s L molding

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Jack Yule uses a similar approach, replacing the batten with an L-shaped molding. Two shallow dados are cut into eac= h face of the molding strips. Contrasting wood strips are cut to the width of the dados and glued = into place over the screw heads.

Here is the procedure I use for mak= ing the batten inlay edge treatment –

After the sound board= has been glued down with epoxy, trim the edge of the soundboard with a laminate trimming bit. I use a scrap of fiberboard to protect the soft spruce from drag marks and scratches from the router base.

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Preparing the Battens=

The battens are ¾” wide and 3/16” thick. Here I’m drilling the = screw holes and a countersink for the screw head every 2 ½” along the each batten. A batten that ta= pers at the treble end makes the treatment a look a lot lighter and less clunky.=

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Attaching the Battens=

The batten is rarely straight, so I pre-drill three or four holes and put in sc= rews at strategic points to position the batten so it overlaps the soundboard ed= ge by an 1/8” along its length. Use #6 x ¾” wood screws. Apply the glue, fasten the batten = down with three or four predrilled screws. Wipe of the squeeze out and drill for the remaining screws and fasten them down.

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Route a Groove for the inlay

The inlay bit cuts a groove 3/8” wide and 1/16” deep. The inlay w= ill cover the raw edge of the sound board along its length, so the height of the cutter has been set so it skims a sliver off of the underside of the batten. The bearing on = the bit has been wrapped with four layers of masking tape to make the channel shallower. The cherry veneer = on this harp is only about 1/28” thick, so the inlay band has to be flus= h or slightly proud of the sound box. &nbs= p;

Testing the fit of the inlay in the channel:

Next, test fit the inlay into the channel<= /o:p>

For the dry fit, the inlay should slide in nicely. Lay a bead of glue do= wn and smear it to the edges of the groove with a= finger. Realize that a= s the glue wets the veneer, it expands slightly.= Use tape over small sticks to hold down any veneer that tries to lift off. =

Iron on the Edge band veneer -

Since it is easier to trim an outside edge, position the edge of the veneer even = with the inside edge of the banding.&nbs= p; A wooden block can be used behind the iron to press it firmly down o= nto the batten as it cools. Trim = the excess using a utility knife with a fresh blade.

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Finishing Touches -

Finish with a scraper and fine sandpaper. The heat activated glue on the veneer can gob up on the bottom of the banding. The scraper is a gre= at tool to remove the glue on either side of the batten and to round the edges just a bit. The eye is = drawn to the flashy inlay and the veneer seams are practically invisible.

Go on to Chapter 8<= /o:p>

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