Martin Guitar Kit Project Build – Part Two

| December 4, 2010 | 1 Comment

This is Part Two of Guitar Kit Builder’s series on building the Martin Guitar Kit by Bob Moore. See the series from the beginning at Martin Guitar Kit Project Build – Part One.

Before I get into the construction details, I want to bring something to the reader’s attention. Humidity can play havoc with wood. It expands and contracts with the amount of water in its cells. When you get a kit home, be sure to let it sit for about a week before beginning your build. If extreme changes in humidity are expected, you might wait until that change has passed. When I started I fretted that the humidity wasn’t quite right, and I borrowed a dehumidifier to try to control it. But then I realized that this is unnecessary. This guitar will be going to a home in the same town with the same weather as where it is being built. Unless you have extreme swings, just keep the box of parts opened and in your home until ready to build it. If I were building professionally, I’d climate-control my shop for both temperature and humidity.

The first step in the actual building of this kit is to cut the sides to proper length. All that’s involved is to secure the sides in a mold (Photo 1). For cutting the sides to length, I used a center line that runs down the length of the mold. I marked each guitar side at the neck and the tail ends and used a square to mark across the side from the top edge. Be sure to use the square on the top of the guitar side because the back is sloped, and the angle will be wrong using the back. I then used a small hand saw to cut them to proper length. Just butt up a piece of scrap against the saw so that it doesn’t wander off the mark.

Photo 1 – Sides secured in the mold

The next step is to join the sides at the neck block and the tail block (Photo 2). The tail block has a face that is slightly curved. This is the part that goes next to the guitar sides. Using Titebond, I applied glue to the entire surface, then pressed it to the guitar sides and, using cam clamps and bar clamps and cauls, secured them together. Cauls, in this case, are just scraps of wood placed next to each glued piece to keep from marring the surface while clamping. Also, I laid down some wax paper under the guitar sides, between the sides and the mold, and on the parts of the cauls that would touch the glued surfaces. This keeps anything from sticking to the guitar.

Photo 2 – Clamping the sides to the tail block

Be sure to get the glue squeeze out early, and make sure the block does not get out of position. Glue is a lubricant until it sets up, and you can ruin a guitar by letting things slip.
I did switch molds for this process. The adjustable mold in the first picture will work fine, but this one makes things a bit easier for me to clamp the neck and tail blocks. I’ll go back to the other mold for the rest of the build and explain its benefits as I go. Now don’t think you have to buy 2 molds, you definitely don’t. If this one hadn’t come as a freebie, I’d have used the adjustable one to clamp up the two blocks. As long as the blocks are centered on the neck end and the tail end, and they are flush or slightly proud on the top, they will work correctly.

The neck block goes on the same way (Photo 3).

Photo 3 – Clamping the sides to the neck block

You might notice that I cut the “wing” off the neck block. You can see the “wing” in Photo 7 in Part One of this series. It’s the part that sticks out to the upper left. I checked around, and it seemed to me that this was a piece that didn’t need to be there. Perhaps Martin uses them to make their guitars more structurally sound. They don’t want returns, so maybe they over-build a bit. It does support the top right under the fret board extension, but it makes getting to the truss rod harder for me. I’m not worried about the loss of that piece. My big concerns with the neck block were to make sure it was centered to where the sides join, oriented correctly and didn’t slip when clamped.

Here’s the view (Photo 4) of both blocks being secured.

Photo 4 – Sides clamped to neck and tail blocks

After the glue has cured, the assembly is put back in the original mold (Photo 5), ready for the kerfing.

Photo 5 – Sides glued to blocks, ready for kerfing

Kerfing are strips of wood that are sawn almost completely thru. They go around the inside of the guitar body at the top and back edges. Their purpose is to give support when the top and back are glued to the sides. They also make the sides more rigid.

Here (Photo 6) are several strips of kerfing:

Photo 6 – Kerfing strips

I apply glue to the back sides of the kerfing, and spread it with my index finger. You want complete coverage, but not so much that it runs down the side. Then press it against one of the blocks and run it around the side, clamping with clothes pins or other clamps as desired.

Even though six string guitars are called “Flat tops”, they normally are not flat. There will be a radius to the top of about 28 feet or so. This is thought by many to be structurally stronger than a purely flat top. At any rate, with changes in weather, wood expands and contracts. A flat top might sink if the humidity goes too far in one direction. For these reasons be sure to keep the top edge of the kerfing about 1/64 inch proud (above) of the edge of the guitar side. Later on, this will be sanded flush, but at a slight angle. If you leave it proud now, you won’t have to sand down the side to get the angle needed.

I only have enough clothes pins to do half of one side at a time, so it took a bit of time. Here’s the completed kerfing job.

Photo 7 – Kerfing completed

Next, I decided to join the back sections together. The back came to me in 2 parts with a decorative center strip. I could have left it off, but thought it might look nice and give the back a focus point.
You can see the separate pieces in Photo 4 of Part One. To put this together, I first made sure the joint between the two sides was flush. This is done by “candling”. Candling is holding two pieces next to each other with a candle or other light source on the other side. If light can be seen between the pieces, they are not flush with each other. Mine had some light showing in the middle of the pieces. To correct that, I made a “shooting block”, which was just sandpaper laid on a piece of glass, and that laid on my granite slab. I didn’t take a picture, but all I did was hold the two pieces vertical and slide them lengthwise along the sandpaper. That takes off the wood at both ends and I know when I’m finished by seeing rosewood dust all along the length of the sandpaper. The possibility of error exists if the parts are not held vertically. I was very careful, and only had a small gap, and it worked very well.

I then made a home-made vise. Robbie O’Brien puts out a DVD on building a kit guitar, and this is copied directly from him. I first put everything together as I wanted it, and then laid a straightedge along one side, clamping it down. Another straightedge on the other side, I made sure that the straightedges touched both the upper and lower bout. This makes sure of even pressure. Once done, I backed out the pieces and glued the edges of both pieces. I put down wax paper to keep from gluing the back to the granite (which would have made a terribly heavy back), and slid the parts along the funnel I’d created. Only a slight push was needed to put clamping pressure on the parts. To keep them from coming out, I clamped some waste pieces at the lower bout. Photo 8 shows the setup with the back in place.

Photo 8 – Back pieces setup for gluing

I had got worried that the back might try to “bow” up because of the clamping, so I borrowed some things (Photo 9) from the kitchen to hold it all down. Photo 10 shows the back when finished.

Photo 9 – Weighting down the back pieces while drying

Photo 10 – Back pieces glued together

Many non-Martin kits come with the back and the top already joined, so you don’t have to go through this process.

I just ordered some purfling, binding, and a tail wedge from LMI. And also ordered some DVD’s on “voicing” a guitar. The purfling will be used on the sides next to the binding, but some will also be used on a particular rosette pattern that I’ve borrowed from Joel Stehr, who’s a consummate luthier and nicely allowed us to use his photo here (Photo 11). I think it will be stunning on this guitar. The rosette needs to be completed and the soundhole cut in before I can begin bracing the top.

Photo 11 – Rosette pattern to be used in the build

I’ll start gluing the top and back braces in Part Three. Hopefully, when that is done, I’ll have digested some of the voicing DVD’s and have a better approach to making this guitar sound good.

Now on to Part Three.

Category: Acoustic Guitar Kits

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  1. avatar Derek Fern says:

    Hi great article I have just purchased a martin kit and looking for any hints on construction. Do you have a plan of your guitar mold?

    Thanks Derek Fern

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