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My Teardrop Project -- A stick dulcimer with a tear drop shaped body

Hi All.

I've decided I wanted to try my hand at wet bending wood, so I'm planning to build a teardrop shaped bodied instrument (most likely a stick dulcimer) by soaking the wood for the sides until pliable, then forcing the wood into a jig/form that was designed around an old 8" hand-drum hoop to form the teardrop shape. I plan to document my plans and build right here in this discussion. As this is my first go at it, any constructive advice you may have is welcome. Right now I have wood for the sides clamped down and drying in the form (jig), and I need to get my design figured out on paper before I get to much further.

Well, here are a couple of photos of my first teardrop shaped side-board drying in my forming rack (jig). My forming rack is pretty crude, but I like to start simply and see where it takes me. If this minimalist forming rack doesn't hack it, I can always modify it, or build a better one from scratch. This rack is the one I built for my elliptical-shaped mountain dulcimer project. The main modification is the addition of an old skin-less hand-drum frame (hoop) around which the wet side-board is positioned and clamped down.

The sapelli wood I'm using comes in 2.2 meter length and measures 5cm (about 2") wide by 0.5 cm (about 0.2" or just under 1/4") thick. I cut a 5 foot length, soaked it for an hour in warm water. The water was originally heated to 42 degrees Celsius, but it was left to cool down as my soaking chamber (a 5 foot length of 3" wide PVC pipe, sealed on one end) has no mechanism to maintain heat for any extended period of time. So, I don't think high heat is pre-requisite for bending sapelli trim wood. But, perhaps (just maybe), heat is needed to help maintain the shape after forming (e.g. minimizing spring-back). Do you know better? I suspect I'm just building a big wooden spring and if I remove it from the rack before I have the head block attached, it will just spring back to is original (or near original) shape. Please let me know your experiences with wood bending.

Anyways, I filled the PVC pipe with the length of sapelli trim wood up with warm water in the bathtub (high tech, yes indeed!). After an hour I removed the board and kind of man-handled it into my forming rack. The wood was still pretty springy, so it took some effort to get it into the form... it wasn't like a wet noodle by any means. But it wasn't that difficult either. Once centered in place, I used a number of clamps (along with small blocks of wood to better spread the force of the clamps across the wood ) to tighten the sapelli wood ("side-board") up against half the drum hoop to help form the teardrop shape. I also added some blocks of wood as "shims" to better position the 2 ends of the side-board.

So, here is a close shot...

As is clear from these 2 photos, I did not have a clear idea of how I was going to attach the neck/head assembly (which I still need to build). To make a stick dulcimer, you need a rather long stick (neck) upon which the fretboard is mounted. As stick dulcimers are played "guitar style", the above body shape seems to be "getting in the way" of your fretting hand, making many frets difficult to reach with your fretting hand cupped around the neck. To correct this design problem some additional re-shaping of the neck will be required. Otherwise, this shape is better suited to a mountain (lap) dulcimer. Here's a couple drawings to help explain what I mean:

In the second drawing, you can see how the upper reaches of the teardrop have to be pressed downward (inward) to form a narrow "top" where the neck can be attached. This means I will have to add some more guide posts on my forming rack to form the "shoulders" that I'll need to attach the neck and head assembly to the body. Notice that these two curves will be "reverse curves" because they bend the side-board in the opposite direction from how the circular drum hoop is bending it. Also, notice how almost 3/4 of the drum hoop's circumference is now being covered by the side-board as compared to about 1/2 of the hoop in the first drawing. With a new forming-rack that implements these two reverse curves, you can bet forcing the wood to bend that much will certainly be a chore. Maybe additional soaking and/or heat application can help by making the side-board more supple.

Also a couple alternative ideas that we could explore are...

1.) Use a smaller diameter drum hoop, say 5" or 6" instead of 8" in diameter.

2.) Use a longer neck, usually resulting in a longer string length (VSL).

3.) Or, perhaps some combination of these two alternative ideas.

The bridge is located 2/3s the way across the drum, but could be moved upward a couple of inches and still be well placed.This could then reduce your scale length if you were planning to increase your neck length.

Well, for now, I'm going to go with the shoulder-less (neck-less) teardrop body design. This means my target instrument will most likely be a short scale lap dulcimer. My next job will be to design and build a "head-block" to close up the teardrop and to form the frame of our sound box. I think I'll also integrate my head-block into the neck (stub) and headstock assembly. Once I'm done with this assembly, I'll mount and glue it to the side-board while the side-board is still (mostly) secured in the forming rack. So, I'll draw the plans for head-piece/neck-stub/head stock assembly now...

Okay! Back with a drawing of my headstock plans. As this first instrument will be a short scale lap dulcimer, there won't be a neck. In its place will be a fingerboard glued to the top of the sound board for pretty much entire length of the instrument. The headstock will incorporate the "head-block", a slotted "chuck of wood" that secures together the two loose ends of the teardrop shaped board to form the frame of our sound box. Here's the drawing which should clarify what I'm talking about.

Well, today, after reviewing the above drawings with machine tuners in hand, I now realize I can't do a slotted head and have the tuner knobs stick out the sides as shown above. Instead, the tuner knobs will either have to point downward like on my other stick dulcimers which feature a slotted headstock, or they'll have to point upward. I remember a few photos of slotted headstock on mountain dulcimers where the tuners were mounted upside down such that the tuning knobs rise up above the headstock, and they say it's a good way to do it as mountain dulcimers are held in the lap or sit on a table when played and tuned. Putting the tuner knobs on top makes them very accessible, but they looks ugly mounted that way (IMHO). Mounting the tuner knobs pointing downwards make them harder to reach, so that option is out. So, I think I'll change my design to a flat (no-slotted) headstock with the tuning knobs pointing out on either side as shown above. Any thoughts / advice on this matter? Well, back to the drawing board...

That's all for now...

-Rand.

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Replies to This Discussion

Permalink Reply by Rand Moore on March 10, 2012 at 2:36pm

Hi Robert.

There you go! Sounds like a great idea to me! But, I think two identically shaped tennis rackets mounted one on top of the other might be needed to give you a deep enough sound box. Remove any netting, plane down the handles if needed and mount them on some kind of wooded platform or other work surface and you're good to go. You may still need a couple of round surfaces like the two halves of the 6" tambourine I used with a bunch of clamps to give it the two reverse curves to make the two ends of the teardrop parallel enough to connect with the headstock without introducing a lot of spring-back tension. I'd also suggest building the headstock beforehand (with tuners in hand) so you don't have to change your design as much as I did. But then, this whole project is an experiment whose eventual outcome will be a set of plans which someone w/o a lot of woodworking experience can us to build an attractive instrument with a bit classier looking and hopefully better sounding sound box alternative to a cigar box. [Not that I have anything against cigar boxes, its just that they are about as common as hen's teeth here in China. And any kind of box sounds better than the tinny-sounding can-jos that I got my start in instrument building 2 years ago with.]

Well, thanks for the tennis racket idea, and keep the good ideas coming. Even i you mean it as a joke; it might just be the idea that sets another builder to give it a go.

-Rand.

Permalink Reply by robert jones on March 10, 2012 at 4:16pm

Wasn't joking, looking at the bottom two pics made me think of the tennis rackets.

I have two identical Wilson rackets. I'm thinking it wouldn't need the 6"dia pieces because of the way the rackets are made, mine are similar to the pic below.

Permalink Reply by Rand Moore on March 10, 2012 at 6:50pm

Yeah, the shape of these rackets look even better for the job the old fashion ones I had in my mind. I wonder if I can find something similar here for cheap. Guess I'll have to add sporting goods shops to the "list" of shops I visit when walking about looking for guitar parts. If you decide to give it a try, let us know how it turns out (photos, too).

-Rand.

Permalink Reply by Rand Moore on March 11, 2012 at 12:02am

While I was at Walmart, I checked out their tennis rackets. I noticed the metal sides of the rackets were rounded, some with two ridges, and some having an extra plastic piece fashioned around the outside of the hoop. So, I feel less inclined to recommend them for use as a forming jig. What you want to form the wood for the sides of an instrument should be a gently rounding surface length-wise, but a flat surface height-wise. If the racket sides are rounded, then the sides (height dimension) may bow out when the soaked wood is forced around them. It might turn out nice, but maybe not. If I were to do it, I'd bolt one racket on top of the other making sure they were perfectly positioned. Then I'd bend my first side board around it, but then keep this first bent board as part of the forming jig, kind of as a "buffer" between the workpiece and the two metal tennis racket frame with their rounded outer surfaces. Another problem area will be the racket handles whose depth will need to be cut down so the rest of the two racket frames can sit on top of each other the right way. In the old days tennis rackets were made of wood, and I feel those make better candidates for a teardrop-shaped forming jigs. Wood should be a lot easier to work in compared to the modern materials they use to build modern tennis rackets. But, don't let me talk you out of it if you think you can make it work. I'm no expert, just giving you feedback of what I foresee as potential problems. They could turn out to be benefits.

-Rand.

Permalink Reply by robert jones on March 11, 2012 at 1:45am

Mine are about 30 years old so a little different than the current ones.

I'll have to add retrieving them to "My Ever Growing List of Projects" . Until then I can't really determine if they would work as forms, but they might.

Permalink Reply by Rand Moore on March 11, 2012 at 12:50pm

Roger that.

Permalink Reply by Rand Moore on March 12, 2012 at 5:00pm

Well, last night I took my teardrop hoop off my forming rack after a 2.5 day drying time for its "second bending". Here's that photo...

This second bending seems to have eliminated much of the warping problem I had, and reduced most of the spring-back pressure on the two ends of the hoop. To completely eliminate the spring-back, I glued in a block of wood between the two sides about halfway up the neck. I clamped that down and let dry overnight. Then, this morning, I rough cut a 2mm thick piece of plywood veneer to serve as the backboard of my teardrop shaped sound box. Then I glued it into place using white carpenter's glue. After clamping i up, I took this photo...

I turned my forming jig around and clamped it all down using a bunch of clamps and cross-boards. I'll let this dry overnight before preceding.

I also noticed a small hair-line crack open up on the lower side of the neck (mid-board, diagonally with the grain) between where the headstock will be glued on and were I glued on that block of wood I added last night. I'm hoping that with the headstock glued on and this new block of wood added last night, the crack won't get worse. When I finish the sound box, I expect a good sanding, followed by a few coats of poly-urethane will make the crack disappear. In the mean time, I'll be watching it.

After the backboard has dried, I plan to add additional wood (which will also be soaked and formed) to the "bottom" of the teardrop to provide more wood to anchor a tailpiece and to better balance the instrument. I'll also have to finish the headstock and glue it onto the teardrop frame. This means I'll have to decide on the number of strings (3 or 4; 4 with paired melody strings). The neck is a bit narrower than I had intended, but I think I will still use a 3cm wide fretboard and allow it to overhang the sides of the neck. Maybe I can add small strips of wood to either side to fill in this overhang and better sculpt the fretboard to the neck. More grist for the mill (my mind). Well, that's all for now.

-Rand.

Permalink Reply by Michael Fred Johnson on March 13, 2012 at 4:27am

Hi Rand

Why not just have the overhanging fingerboard with radiused edges for comfort and forget about filling the overhang.

Permalink Reply by Rand Moore on March 13, 2012 at 8:49pm

Hi Michael,

Good idea. I assume you suggesting to just rounding off the corners on an otherwise flat fretboard and not a radiused fretboard like on real six sting guitars. The former is easy to do, but the later would be pushing me beyond my current woodworking skill level. I prefer to keep it simple and go with a flat fretboard with rounded edges.

I was also thinking that if it was going to be a lap (mountain) dulcimer, then I could put in thicker raised fingerboard with the under board(s) narrower than the top. I could make it like a raised bridge with several piers and several spans like on my first mountain dulcimer. But since re-bending my teardrop with the reverse curves and long neck, I've been thinking "stick dulcimer".

The other concern I have is the extreme depth of the neck. It's 5.4 cm thick and fills up much of my hand even before I curl my fingers to fret chords and the like. I'm worried it will be harder to fret than most my other instruments unless I lie it down and pay it like a lap (mountain) dulcimer. You see I'm still teetering back and forth between "Is it a small lap-dulcimer?" or "Is it a stick-dulcimer?". Dimensionally, it falls between the two, and maybe if built right, it could be played either way. But, because of the string layout difference, I've got to decide which it will be.

One other problem, the headstock is also really thick around fret 1. So, I was thinking of cutting off the ends of the outer two boards of the headstock about 3 or 4cm shorter while retaining the inner block of wood. The inner block of wood and the two smaller slots should be sufficient to glue the 2 ends of the teardrop body to the headstock now that I have the spring-back tension o the teardrop hoop under control. Here's a doctored photo of what I mean...

If I go the stick dulcimer route, and I want to make it really easy to play, then I think I should cut off most of the "neck" off my teardrop sound box and mount in its place my standard head & neck sub-assembly. This would most likely be a "neck-almost-thru", something a lot easier to build as compared to a "bolt-on" neck. I'll be giving it a lot more thought in the next few days. Any input is welcome.

Well, that's all for now.

-Rand.

Permalink Reply by Habanera Hal on March 14, 2012 at 1:10am

Rand -

Here's an idea for the overhanging fretboard - would be really unique: http://www.dollhouseminiatures.com/supplies/crown.htm

As to the thickness of the neck at the first fret, looking at your picture I think cutting back the two outer boards would work, but I would do it AFTER you glue the body on. Just don't spread glue on those edges - you would then have the length of the boards to apply more pressure when clamping. After the glue dries and you cut them back, you could blend them into the neck with a nice radius. If you have any concerns about the strength, you could run some dowels through the body/headstock block joint.

Permalink Reply by Rand Moore on March 14, 2012 at 10:55pm

Hi Habanera Hal,

Unfortunately, that link seems inaccessible from China, but I can imagine what you mean... miniature crown molding. I'll see what I can come up on this side of the Pacific that can serve the same purpose. Was thinking a bamboo skewer trimmed to length might be okay. I have skewers of 2 diameters that I can play with. Hmmm... I wonder if I can soak them and roll them into spirals and other decorative shapes. Food for thought.

As far as trimming the outer two boards of the headstock, I don't anticipate clamping problems if I cut them before I glue them up as there is no more spring-back tension in the ends of the teardrop hoop now that I've glued another "block of wood" about halfway up the neck to handle the remaining spring-back (that had been already significantly reduced after my second bending which introduced a reverse curve to each side). Time for a picture, I guess...

I made the "block of wood" out of the same wood (board) as I used for the center of the headstock to match the thickness. And as you say, if spring-back gives me anymore problems, I can always come back and add a dowel or two to reenforce the "head-to-body" joint or this "block of wood" joint. I've got a few more photo I'll add later.

-Rand.

Permalink Reply by Habanera Hal on March 15, 2012 at 2:22am

Hmm, sorry you can't access the link. Here's a couple of pics of two of the 16 styles they show. Sold in 24" lengths, average between $1.80 to $3.00 a strip.

The whole project looks like it's coming along nicely. Have you thought about what you will use for the bridge and/or tailpiece yet? The "hollow" neck is intriguing, too. Adds more volume (size) to the sound chamber. Have you thought about maybe adding a piezo in that area under the fretboard?