Of all the fixtures and jigs in my shop, perhaps the single most important is the body mold, a wooden form that holds the precise shape of the guitar body during construction. There are several acoustic guitar body molds readily available for purchase, so long as you happen to be building the instrument the mold was sized for. But what do you do when you set out to build something different, a guitar that deviates from the popular, factory-made guitar shapes and sizes? You make your own body mold, of course! This article details my particular approach.
When I alter or introduce a new guitar shape, I will first lay it out on paper. Paper is great for sketching out concepts and making measured drawings for future reference, but a paper template wouldn’t have a very long or useful life in my workshop. I will create a set of acrylic or hardboard templates from the paper drawing.
Creating a body pattern template out of clear, hard plastic by hand may seem a bit tedious, but it will serve multiple purposes and withstand repeated use, so it is well worth my efforts. My shop-made templates are sized to the outer dimensions of the guitar body. I scribe the body shape onto my choice of template material, rough it out on the bandsaw, clean it up at the disc and belt sanders, and perfect it by hand.
Cf Martin Mold
A simple shop-made body mold is constructed by laminating multiple layers of a strong, stable material into a block, band-sawing the block lengthwise into two pieces along the centerline, tracing the outline of the body of the guitar onto each half, band-sawing the contours out of each piece, and utilizing some method of holding the two pieces together. If you are curious as to why the mold is cut in half, as opposed to being left intact, it is to allow for disassembly and removal once the guitar body is complete. It could be risky to build an entire guitar body in a one-piece mold and then attempt to remove the body from the mold once complete. It is much easier to spread the mold apart and take the body out.
I prefer to use plywood for my mold and jig construction. I don’t much care to deal with MDF sawdust, anymore, and cut it as little as possible. I would not recommend using the cheapest plywood available, as the voids in the plys can introduce inaccuracies in your finished work if ignored (and they are just aggravating to deal with). I prefer at least five (5) layers of plywood; three (3) inner layers of 3/4″ and two (2) outer layers of 3/8″ or 1/2″. All five (5) pieces are cut roughly to 24″ x 24″ square.
I dry-assemble the plywood pieces (without glue), check them for square them on one corner and clamp them together. I lightly draw my guitar body shape on the plywood as a reference, only (these are not cut lines). Two (2) holes are drilled completely through all five (5) layers in (what will become) the waste area of the plywood, into which dowels will be driven after applying glue.
Inch D45 Mold 12 String Koa Wood Black Fingered With Acoustic Guitar
Doweling the plywood pieces, while entirely optional, allows me to focus my attention on simply clamping the plywood together, instead of having to
Worry about keeping five (5) separate pieces of wet, gooey, glued wood aligned. I drill a 3/8″ hole into which I will hammer a 3/8″ hardwood dowel. While most any diameter of dowel will do (1/4′, or 1/2″, etc), too small a diameter and the dowel can break while I am hammering it in.
The plywood pieces are unclamped, staged, glued, re-assembled, pinned together using the dowels (for alignment), and clamped back together again. Your favorite wood glue is applicable, here, as most anything will do. I have probably used all of the available glues over the years: whites, yellows, epoxies, though I have been using polyurethane glue for lamination projects like this, more and more. If you do choose to use (or audition) a polyurethane glue such as Titebond or Gorilla, be sure to lightly wet the wood prior to thinly applying the glue. Polyurethane glue depends upon moisture in order to cure. I apply the glue to one face using a card scraper or thin piece of wood, and I wet the other face with a spritz bottle of water. Polyurethane glue will expand up to three (3) times it’s volume as it dries, so a little goes a long way.
New Adjustable Mould
Once the clamps are removed the (extremely heavy) plywood block gets trimmed and trued up. The length of my finished body mold will be equal to the length of the guitar body plus 1-5/8″ at both the neck and tail block areas (2 x 1-5/8″ = 3-1/4″). The width is equal to the width of the guitar body at it’s widest point, the lower bout, plus that same 3-1/4″. This block is heavy at this stage, so trimming it to size now reduces the weight I have to deal with in subsequent steps.
“It is critical to the design of my guitars, particularly regarding how the neck joins to the body, that the portion of the body mold supporting the neck block be perfectly true. It must measure 90° perpendicular to the centerline (which I derive from one edge) and be cut at a 90° right angle from the face.” — Christopher Cozad
It is time to cut the block in half, lengthwise, a step I can perform at the bandsaw or tablesaw. If I cut the block in half on the bandsaw, I pass the cut blocks across the table saw to perfect the bandsawn edges.
Martin Guitar Kit Project Build
While the block is still relatively square (no curves or shapes have been cut into it), I will add the clamping mechanism(s). There are many ways to hold these plywood blocks together, including using a large wood screw. It is very common to see DESTACO clamps used, either on both the neck and tail block ends, or a single clamp on one end and a hinge on the opposite end. I find these clamp parts tend to get in the way of trying to clamp head and tail blocks to the sides during glue-up. Another popular method extends the mold at both the neck and tail blocks, and allows for a bolt to clamp the two sides together.
Another popular method extends the mold at both the neck and tail blocks, and allows for a bolt to clamp the two sides together.
I have developed a slightly different approach. I have never had a reason to completely disassemble my body molds in order to remove a guitar body. A simple loosening is all that is needed to extract the tightest of guitar bodies.
Acoustic Guitar Chocolate Mold
At each end of one of the mold halves, on the inside edge, I secure a 5/16-18 threaded rod into a cross dowel. The 3/8″ hole for the rod is centered across the width of the five (5) boards, set back 13/16″ from the end of the block, and drilled 2″ deep, where it intersects the hole for the cross dowel. This 7/16″hole is also set back 13/16″ from the end of the block, though it is drilled on the face of the block 1-3/4″ from the inside edge. Two (2) 3/8″ aluminum dowels (hardwood dowels will also work), 2-1/4″ long, sit parallel to each rod. These rods act as alignment guides, keeping the mold from shifting out of place when it is opened and closed again.
Note that the 3/8″hole for the cross dowel does not extend all the way through, though it would be fine if it did. It is replaced by a small hole, just large enough to access the cross dowel for positioning, if needed, during initial assembly.
Each half of the wooden mold gets mirror image holes drilled into it’s edge. I can accurately position these holes by first laying out and drilling holes in the edges of one of the halves. Into those holes I place small inserts known as dowel centers, lay the two halves together, edge-to-edge, and press them together. The dowel centers mark the exact centers of the drilled holes in the one half onto the correct location on the opposite half.
Solera — Lutherie Guitare.org
The twin holes that house the aluminum dowels are drilled to the same depth, 1-1/8″, as their mirror mates. The center hole housing the threaded rod, however, gets drilled all the way through to the opposite edge of the wooden block. I have a long drill bit just for the task. A secret to getting a manually drilled long hole to work each and every time is to drill from both edges and meet in the middle. The hole is a bit oversized (larger than the threaded rod), in order to provide a margin for error. You do not want to make a mistake at the edge of the material, where the pieces mate up.
Once the block is able to be assembled and can be accurately secured in a closed position
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