Chapter 8

The Soundbox

    Hi!  Welcome back.  While you were gone, I have been busy here.  Having the neck and the pillar almost ready for assembly, I realized that I had to get down to the hard part and start getting the body of the harp, or the soundbox, put together.  This is a difficult part of the job.  I've got 6 long tapers, with miters, and the soundboard to put together into one unit.  And here I am with only 2 hands.  I knew I had to devise some kind of fixturing to hold all of these pieces together while I did the necessary work.  So I made some temporary braces to fit inside the box and hold the pieces in their proper relation to each other.  Some pieces of 1/2" MDF that were laying about the shop fit the bill exactly.  I took some measurements, transferred these to the MDF, band sawed the braces close to the lines, and then sanded them to fit on that new disk sander.

    Here you can see what I came up with.  The bottom brace, the larger one, has holes drilled in it near the edge to accommodate some small clamps.  The smaller brace near the top of the soundbox, is just held in place with some rubber bands.  Notice how I crowned the top of this brace so that the rubber bands can help to hold it in place.  At this point the assembly is fairly secure and I can move it around and work with it.

    The first thing I need to do is locate the top and bottom of the harp body on these pieces.  Remember when I cut them out and did all the tapers and miters, I intentionally left the pieces long.

    Here is a closer look at the clamp assembly.  By using my bevel gauge and transferring the angle of the sides to my disk sander, I was able to sand a matching angle on the sides of these braces.

    Here I have taken this assembly and positioned it right over my full size drawing.  I used blocks and shims and adjusted the assembly until the centerline was parallel to the table top.  I shimmed it until the front edges of the sides were perpendicular to the table top.  Once I was satisfied with it's location, I could use my square to transfer the reference points from the plan to the harp itself.  I did this on the front and back, both top and bottom,  and on both ends.

    I was then able to lay the box down on it's front, and complete the lines around the sides that will mark where I need to cut off the excess

    Doing the same for the top of the box.

    While I still had it all clamped together, this was an ideal time to take some measurements for the size of the soundboard.  These measurements turned out to be 9 & 1/2" wide at the bottom, 3" wide at the top, and almost 31" long.  At this point there was a large sigh of relief you could probably have heard in New Jersey, as these measurements were almost exactly what I had planned and hoped for.  I just love it when a plan comes together.

    After all of that, it was time to take the thing apart again.  Using the table saw, I carefully cut off the excess from each end of all 6 pieces.  Here I'm holding a piece of scrap wood against the exit side of the cut to prevent splintering on the fragile mitered edges of these pieces.  I also cut them just a little longer than the marks, so I can fine tune the fit after they are assembled and ready for the top block and base of the box.

    This was also a good time to cut a groove into the sides of the box, near the front edge, to receive the soundboard.  This groove is 1/8" deep, and just over 1/8" wide, located 1/4" from the front of the side, and on the inside of the box.  There are as many ways to attach a soundboard to a harp body as there are harp makers.  I've seen so many different ways to do this, I can't remember them all.  But this is how I like to do it.

    You can see in this sketch that I let the edges of the soundboard into small grooves cut into the sides of the box.  These grooves run the length of the box from top to bottom.

    Just in case any of you aren't sure, this sketch is intended to show a cross section view of the soundbox.

    There will also be another small brace added to the joint between the side and the back of the soundboard.  The front edges of the sides will get a smooth radius before assembly. 

    The sketch also shows the interior bracing that is going to strengthen the miter joints that run up and down the back and sides of the soundbox.   Cutting these braces will be one of the next steps, but I also need to rough out the soundboard to ensure that it is going to fit into these grooves I just cut.

    Now I expect at least some of you are going to see the humor in this step.  Here I am laying out the soundboard on a piece of PLYWOOD!  But this is not the kind of CDX ply I was talking about back in the introduction to this project.  This is a very special piece of ply.  It is 1/8" thick, with 3 plys.  All 3 plys are Sitka Spruce, and there are no voids anywhere in any of the plys.  It is beautiful material, produced specifically for soundboards like this.  And if any of you are curious, this one piece, 29" X 59" runs about $110.00, minus shipping charges.  This is one operation where you really don't want to say "Oops!"  I have drawn my layout lines just slightly larger than my calculated dimensions, and it will be trimmed to final size just before assembly.  Right now I'm just concerned with the fit into the grooves I've cut into the sides of the soundbox.

    And another sigh of relief is in order, as the soundboard just slides perfectly into the grooves.  Notice here that the grain of the Spruce runs from side to side, instead of top to bottom.  This is another point of tradition.  If this soundboard had been fashioned from solid Spruce stock, the grain would have to run this way for strength.  Grain running up and down would have a nasty tendency to split along the center line where the strings penetrate the soundboard.  The same holds true with this ply that I'm using.  Having the front and back plys run from side to side provides for a much stronger soundboard.

    The next step is to mill the 45 degree bracing material that will strengthen the mitered corners of the soundbox.  First, I make sure that my blade is kicked over to an accurate 45 degrees.

    First I trued up a piece of Maple 3 feet in length, then I cut a 45 degree angle on each edge.  Repositioning the fence and the depth of cut, I then cut the first leg of 2 of the braces.  These legs are 3/16" thick.  The pencil lines should give you an idea of what I have in mind here.

    Here I have one of the braces cut free, and have just set the depth of the blade to intersect the first cut on the second piece.  These operations are repeated again on the scrap pieces that are cut free, to give me a total of  4 of these angle pieces, each 3 feet long.  The width of each leg will be trimmed during assembly, and near the top of the box they will have to be tapered as well.

    And here are the interior bracing pieces, all cut from the same piece of stock.  The small rectangular pieces were all that was left after I cut the second set of angle braces, and after trimming off the angled edge, they are perfect for use as the soundboard braces. 

    Well, that's all the fun and games for today.  Be sure to check back soon to see what happens next.

Move on to Chapter 9

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