Building: Chapter 3. This tutorial on building an acoustic guitar is broken up into six chapters. Jump to chapter: 1 - 2 - 3 - 4 - 5 - 6

Chapter 3 - Building The Guitar Body

Making The Mold
The first thing we need is the mold. With a piece of tracing paper over a good piece of paper, copy the profile of the guitar body. Cut this out carefully and transfer the profile to your mold material. You can purchase molds for most of the standard profiles. Be careful, if you use a bandsaw. They seldom hold the true square that is needed for a good guitar.

To make a cardboard mold get a few good pieces of cardboard. A grocery store will have that. Cut the patterns out very carefully with a very sharp utility knife. You should make this in one piece. It will be cut away when the body is finished. I would suggest you make 3 cut-outs if possible. You can space them with 3/4 in pieces of wood. Be sure they are as exact as you can make them. The squareness depends on this.

Initial Mold Assembly
With the mold ready you can now start the guitar. Get your sides and a few clamps and cauls ready. On the neck and tail block, mark the center lines. Be sure you get them as close as you can, the neck block being the most critical. The top of the block has the cantilever for the neck. The slot in the block is for the truss rod nut and the adjustment hole is in the largest brace. It is best to dry run to check for center. The neck block should be center to within 1/4 inch at the tail block. The joint of the sides should be the center. That is the target you are gauging to.

For a non-mold assembly, get the yellow glue and some masking tape. I found that gluing the edge and taping them together makes handling them a lot easier than wrestling all the clamps and cauls. With the top Identified, and working on a flat surface glue the blocks into position, with all the flat parts facing down, the neck block with the groove should also be down, let sit and allow the glue to dry. You may wipe off any excess glue with a damp rag. Try to get as much off as you can.

With mold assembly, I like to set the sides in and check the fit. Very seldom will you need to trim but if you do trim both sides equally. I smear a tiny amount of glue to the edges and set them into the mold, top down. Then glue in the blocks. I will have a jamming stick that forces the block against them mold, then using spring clamps to hold the open sections to the block and let sit overnight. Should you have had movement of the neck block you can remove the block with steam or carefully use water and let it soften the glue and redo the joint.

Gluing Up The Ribbing
With the glue dry you may now glue in the ribbing. I start at the neck block and work my way to the tail. Here is where the clothes pins come in handy. When you start one strip against the other, try and keep a uniform gap, don't butt the ribbing against each other, you may develop a buzz. Remember the guitar does move. Keep the ribbing as flush to the edge as you can. I like the yellow glue on this. Again wiping the glue away with a warm wet rag. Let sit and check that nothing has shifted. I do one side at a time. Allow an hour or so for the glue to set. Now the side support braces can be attached. They are the thin strips. I use the spring clamps for this. Trim them to fit between the ribbing. They should be put in the high stress areas. Check the print or instructions. It they are not specific, I set them at the shoulder curve, the waist, and the bout.

Now that you have a guitar profile, carefully work it into the mold. Take your time. You can use pieces of cardboard to wedge the sides against the mold. You may also want to study the neck joint and see that the joint. I like to sand this area as flat as possible for neck setting.

Gluing Up The Back
You can now glue up the back. With the jointed edges glued, place the purfling strip into the glue and using pipe clamps glue it up. My preference is to use a piece of plywood. I use tape at the area of the glue joint on the plywood. It is no fun trying to get a glued up back off a piece of wood it's accidently glued onto.

Clamping Without Pipe Clamps
If you don't have any pipe clamps I have a trick. Take a piece of plywood at least 1/2 inch think and 24 inches wide. Using C-clamps and a long piece of wood, clamp one side down about 1 inch from the joint, leaving more than 1/2 of the plywood exposed. Take a 3-4 inch wide piece of wood, a little longer than the back piece and cut it on a diagonal over the length so it looks like 2 long wedges. Now set the back pieces together DRY. Draw a line. Do not rough cut the back until it is together. now you can take the 2 wedge pieces and set them 1/4 inch over that line. This wedge will do the clamping.

Attach the outer most wedge. Clamps, or screws are fine. before applying the glue test fit the back and try the clamp. Don't over tighten it just snug it. You want to see some glue squeeze out but most important you want the joint to close. If it looks good, apply glue and clamp. Make sure you check the purfling strip. You want that as near flush as you can get it. If not adjust the wedge. When the back is dry you can apply the cross grain bracing first. I use 2, 2X4's and clamp the strip between them. I also apply masking tape first so they don't shift. You may also sand them and give them a finished look either before or after. I have done it both ways and like to do that after they are glued onto the back but before the bracing is put on.

Cutting In The Back Bracing
The back bracing is now cut in and dry fit. Take your time. I use an Exacto knife to cut the outline and pop the chip out with a chisel, cleaning up all the glue. I like a nice snug fit, if at all possible. I also sand the braces a little before installing, but be careful not to sand the bottom edge. Use a small block to keep the corners sharp. Before you glue them in, I have another little hint.

You will have to trim the braces and inlet them into the ribbing. You can do that with the braces attached but I like to do the inleting before they are glued on. I first have the back all set and ready to get the bracing attached. I know where they are and the guitar body is in the mold. I mark the center of the back. I have the braces taped on the back and set it on the guitar. I then flip the whole thing over and mark the location of each brace, and mark each brace where the ribbing crosses it. You now know where the bracing is to end up and the rough length of each brace.

What I do now is trim the brace to fit. I want the brace to fit inside the body, not through it. Carefully trim the ribbing so the braces fit. I like snug, not that you have to force it in but a nice clean fit. I take it slow. You can use an Exacto knife or a Dremel tool. You want the brace to be flush. If the ribbing is not flush to the edge, you may sand it to make it flush. Remember the radius, you don't want to sand a flat into it. When all is dry fitted, set the back onto the bracing. Flip it over and tape the braces onto the back again and mark the end locations of each brace. You can now glue up the back. I used to use a heavy and firm piece of foam. This allowed the radius of the braces to shape the back. I now use a gobar clamping system.

Bracing The Top
The top should also be prepared and braced. Again you can rough the inleting in but you need to be aware of the centerline. It is good to point out now that the only top bracing that will be inletted is the X braces. The tone bars and upper bracing, be it the A frame or the regular braces stop just short of the ribbing. If you want to be sand the braces, you can so just be careful not to sand a radius on the bottom of the braces where they are glued to the top.

Installing The Bridge Plate
The bridge plate will go on last. I like to see the bridge plate against the X braces but not into them. Some day in the future the bridge plate may need to be replaced, so use white glue on it.

Gluing Up The Guitar Body
You now are ready to glue up the guitar body. This is the time the neck angle needs to be assured. If you are not careful you will need to do more work when setting the neck. I use a square and note where the gap is and measure that. Usually you need to place a shim on the bottom. A doubled up business card usually is all you need. You don't want to try for perfection, just a slight angle.

Before gluing up the box, eyeball across and check that the body is still flat across the top. If there is a up and down,take a long sanding block and gently work it flat. You want to see the neck block and all the top pretty flat. Don't worry too much about the back yet. You can rough the top and back to shape, leaving about an 1/8 inch for final trimming when are sure the dry fit is good. . You can leave more if you are not sure. It is easier to take off than to put on.

Check that the top is tight against the sides and that no gaps are present. You also want to check center line. It is also a good time to talk about the tail piece. I have put them in at the beginning but I like to do them after the top and bottom are installed. When you are happy with the fit, dry fit and tape into position. Just a few pieces will do.

Fitting The Back
Now lets dry fit the back. Mark center and place it on. This will not sit flat because of the radius so tape the neck and tail area. Are the fits good and center within 1/8 inch? If not you may need to make a few adjustments. when you are satisfied with the fit you are going to look at the sides. Do they look pushed out or in? If the do look and see where you need to trim the braces and take small bites. A small razor saw is good to cut them and a chisel will pop them out. Be sure to clean off any glue. Refit and check again.

Gluing Up The Top
When you are ready to glue up, I like to do the top first. Use yellow glue and spread a nice even coat along the ribbing. You can tape the top down if you don't have clamps, just be careful and watch what your are doing. The back is a little trickier. I lay an old towel or a clean piece of cardboard down and use it to protect the top. We don't want any scratches or little dings if we can avoid them. I have a press to glue up the body but you can use some of those old weights you have in the cellar, just pad the with cardboard. you can also sandwich them down with rope and wrap it.

Trimming The Top
When the glue is dry you can finally trim the top with a good router flush trim bit. If you get any tear out, remember that the binding will go on. If tear out is worse than the binding will cover, save the little wood scraps from the roughing out and you can repair the tear outs with them. Using a sharp chisel pare away a straight edge and glue in a piece. Masking tape will hold it well enough.

I like to use a press as I stated before but for beginners, an inexpensive solution are spindle clamps. An 8 inch carriage bolt and a hole saw does the trick. Using a decent piece of 3/4 inch wood or better. Use the same size bolt as the center drill in the hole saw. I like the 1 1/2 inch hole saw. Make a pile of them. At least 10 for the glue up. They will clamp the top and back very nicely. You should cut a series of blocks in the curvature of the guitar, both top and bottom and it will close it up well. You may need to drill holes in the mold to accommodate the bolts.

Removing From The Mold
When all is done and you are happy with the body you can take it out of the mold and inspect it for any defect that you may have missed or built into it. If you see gaps between the sides and the top or back, you can repair them now. I like to wet the area with water and let soak a few minutes, Then work in some small piece of sandpaper and clean out the area, damped it again and work some glue in with the finger and clamp it tight.

Sanding And Filling
When all is trimmed you are ready to start some sanding. Do not sand the sides yet. only the top. Depending on the finish you are using I like a good sanding sealer at this point. Only on the top. It will help later when you do the filling. It also toughens up the top and makes finger marks less likely to happen. I use a good vinyl sealer but shellac is also good. After the top has been sealed you can sand the sides and back, and seal also. The reason you are sealing is first, it stops the oils from your skin seeping into the wood and putting ghost marks in the finish. Second, you need to seal the wood for the filling process. There are a number of thoughts on when to fill and when to bind. I like to bind before filling, so the next step is going to be the friezing process.

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