steven popkes - mando 01

Mando 1 is a tribute to someone who knows very little about building an instrument, wants to do it from scratch and doesn't have much talent.

I looked over a lot of pictures, read a number of plans and perused a bunch of sites. I came up with a basic approach.

To my mind, string instruments are a continuing compromise between tension loads and compression loads. You want a tension load on the system from the strings-- that's where the sound comes from. 

String instruments such as guitar, violin, mandolin or lute, are essentially the same sort of instrument: there's a headstock where the strings are attached and tuned, the string is bent over a nut and then stretched over a fingerboard. Its sound qualities are transmitted to the belly of the instrument by some kind of a bridge to which the other end of the strings may or may not be attached. The job of the bridge is to translate the vibratory motion of the string into vertical compression of the belly causing sound.  The difference between string instrument types  lies not with the nature of the soundbox construction or the ornamentation of the headstock but with the way the bridge transmits sound to the belly.

It seemed to me there were three classes of instruments based on bridge construction-- shown in the adjacent drawing as type A, B or C. In type A, used commonly in guitars, the bridge has a riser-- or saddle-- over which the string comes. In this case, the saddle is the mechanism of the translation of string vibration to vertical motion which is then amplified by the bridge. The bridge also serves as the anchor point for the strings. The tension load on the type A instrument is up, from the string anchor point and towards the headstock. The compression load is the load of the string tension across the saddle down on the belly.

Type B, used in some guitars and all violins and mandolins, is a bit more sophisticated and involves considerable more loading. The string in this case, comes across a bridge (which may or may not have a saddle) and continues to attach to a tailpiece. In a type A instrument, the force that can be put on the bridge is limited by the strength of the glue holding down the bridge and the wood of the belly. Regluing a bridge back to the belly of a guitar is a common repair.

Type B instruments get around this whole problem by moving the attachment to the tailpiece. This has two big advantages. First, the belly no longer has to serve as the basis for attachment. Bridges are often completely loose on a type B instrument, held only in place by the tension of the strings. The wood under the tailpiece can be quite heavy and the tailpiece itself is often made of metal.

A second advantage, since the bridge is no longer an attachment point, is the tension on the strings can be increased considerably. This allows more energy to be transmitted to the belly and, therefore, louder tone. But along with the increase in the tension load comes an increase in the compression load on the belly. The belly has to be stronger, either with stronger bracing or with strong wood. Violins, for example, are carved out of a piece of wood and not assembled of thin planks such as a guitar.

Type C, included here just for the sake of completeness, is used in lutes and other older instruments. In this case there is no saddle or tailpiece. The strings connect directly to the bridge horizontally or nearly so. In this case, there is no direct translation of the string vibration to a compression but instead the bridge vibrates up and down at an angle. It's very inefficient but gives a very interesting tone.  

Type B instruments, with their tailpiece construction, are complicated. The belly has to be braced against the compression load. In addition, there's a heavy joint where the neck meets the body of the instrument and an equally heavy joint at the base where the tailpiece has to be mounted. These joints serve to transmit the tension load between the ends of the instrument without crushing the delicate soundbox in between. The top and bottom joints serve to transmit the loads to the sides of the instrument which are made of thicker wood.

I didn't want to mess with all that. 

Instead, I decided that I would build a mandolin with a "spine" where the there was one load member that extended throughout the instrument. Some banjos are built this way.

This had the advantage of being able to cut the spine out of one piece of wood-- as I said, I wasn't very talented. The drawing at left shows the spine in white surrounded by the gray of the poplar block I cut it from The poplar block was 2x6, which pretty much determined the dimensions of the instrument.

 

This pipcture shows the spine when the back was attached to it. For belly and back I used a spruce laminate I found at Michael's Arts and Crafts. Unfortunately, as we shall see, I mixed the belly and back up.

Here's a closeup of the joint between the base of the fingerboard. That notch was going to cost me some grief later. The little cubes were bits of wood I found at Michael's that I used for the base to glue the sides to.


Close up of the base of the headstock as I had cut it out. This was where the pegboard would be mounted. I was worried that the force of the string tension would pull that thin wood apart. 



The gluing of the "kerfing" to support the sides.

 

 

Here are the belly and back being glued in place. Because of the nature of the spine it seemed easier to built from the outside in. 



Clamping. Clamping. One thing I learned from this project was how to clamp.



Once I had the front and back put in place I started on the sides. My plan was to leave a little bit of the spine hanging out to serve as a tailpiece. This turned out to be a mistake later. here the sides are being glued to the block at the base. I used airplane spruce, a wood laminate so thin you can cut it like paper. It's more like a stiff veneer than real wood.


 

Here you can see inside of the mandolin. I did put in some vertical members to space between the belly and back.


A pretty shot of clamping and gluing.


One problem I had was to curve the wood around the sides. Remember, unlike normal sides that have been steamed into place, this stuff was more like paper. Duct tape worked pretty well but I had a little trouble getting the adhesive off. Later, I discovered, many people use masking tape.

 

Here's a picture of how the sides were measured before being glued.


Here's how it looked once I had glued the bits together.



The headstock piece, since I had made it from two inch poplar, was far too thin. I used gorilla glue to take two pieces of oak and form a sort of laminate to give it strength. Seemed to work pretty well.


These pictures show how I took the resulting headstock and put in the tuning machines. Stew-Mac has a sweet adjustable jig.

 

 


I spent a lot of time trying to figure out the finger board. Here I was trying one version, a simple strip of the same material I had made the belly and back from. In retrospect I should have glued it in. More about that in a bit.

 

These are pictures of the front and back of mando 01 after I'd put all the pieces together. Note the big oval patch on the front. Clearly, I'd mixed the front and back sides. It was at this point I decided that I would black lacquer the whole thing.

 

I faced the headstock with bloodwood. But I was still worried about string tension over that thin neck. I had made one mistake earlier in not cutting a spot for the nut. So I decided to take a mistake and turn it to my advantage. I cut a pice of rosewood and made a back for the nut, extended a bit to also serve as a brace for the headstock.

 

Another nice headstock picture. 

 

Here are a set of pictures showing the "finished" product: no frets yet and unstrung.  I had originally thought to make the mandolin fretless but after playing with a mandolin in a store I decided I didn't want my hands turning into hamburger. 

These next two pictures also show the true mistake I made. The big one. The nasty one I haven't solved as yet, though the instrument is fretted. Notice the fingerboard is flush with the belly. I thought this would be cool, the same way it looks cool on my lute. Bad move. Turns out that the increased tension of the strings also requires increased angle across the bridge. There's only two ways to solve that. Either the strings have to be elevated or the mandolin belly has to be cut away at an angle. Wendy has a mandolin of that type but I haven't put in a picture of it.

Here's a good picture of the back. Notice that notch is gone? I cut a piece of poplar and fit it in and sanded it down. Didn't suck.

Another picture of the Not Sucking back.

 

 Back of the headstock.

  

 This is (obviously) the front of the mandolin. Note that the spine can be seen through the sound hole. Certainly, it's ugly. Likely, it messes up the sound. In a future model I think I'll curve the spine. Then, I'll split the back into two pieces and fit them into a slot on the spine's side.