Building the Neck Blank for the Steel String Acoustic Guitar

In the broadest sense the process of building a neck has two major operations. The first is building up a blank that is the first order approximation of what the finished neck will look like, and the second is successively taking away wood from that blank to yield the final shape of the neck.

There are a number of ways to construct the blank that will eventually become the neck of the steel string flattop guitar. The method detailed here is probably the one that uses the least amount of wood, a good thing as the prices of mahogany and other woods traditionally used for the necks of acoustic guitars continue to climb. This neck blank makes use of a scarfed neck joint and a built up heel block. It can be implemented using hand or power tools.

The headstock scarf joint has a lot of advantages in addition to being miserly with wood. It makes for a strong headstock, plus the joint is completely covered in the finished instrument on the top (by the headplate) and on the sides (by the headstock width extension pieces) so even if your joinery is less than perfect it is mostly hidden from view.

Last updated: September 11, 2018

Critical Measurements

I make the neck blank from a single piece of wood. The dimensions of the piece of wood you'll need to start off with will depend on a number of critical dimensions of the instrument you are building. Before starting, the following dimensions must be taken from the instrument plan:

  1. NL, the length of the neck from where it joins the body of the guitar to the start of the headstock;

  2. DL, if the neck joint has a dovetail or straight tenon, the depth of that dovetail or tenon;

  3. HL, the length of the headstock;

  4. NT, the thickness of the neck shaft at its thickest point;

  5. HT, the thickness of the headstock;

  6. FW, the width of the fingerboard at the body join;

  7. LL, the length of the neck heel, from the underside of the fingerboard to the bottom of the heel;

  8. LD, the depth of the neck heel;

  9. HA, the angle of the headstock WRT the fingerboard surface;

  10. LA, the angle of the surface of the neck heel that contacts the body WRT the fingerboard surface;

Choosing Material for the Neck

The traditional material for acoustic flattop steel string guitar necks is Honduras Mahogany. This is an ideal wood, offering relatively light weight, high stiffness, stability, and ease of carving. It was traditionally pretty inexpensive too, but the price is now going up dramatically. I'd still recommend that first time builders stick to Mahogany, but any species that offers similar stiffness, density (weight), carve-ability, and stability can be used to good effect. Sapele is a good alternative to Mahogany and (to me) it is generally more visually appealing. Do keep in mind that stability is a very important quality of the material for a neck. Mahogany has an interlocking grain that makes for an amazingly stable material. It does not change shape much with changes in humidity. You can certainly use less stable wood like soft maple for an instrument neck but it is wise to be sure the billet you use is perfectly quarter sawn. Unless you hand select the piece (and even if you do) perfectly quartered wood is close to impossible to find these days. So if you use maple or a similar wood I would highly recommend building up the neck blank billet out of laminated pieces. Three pieces of rather haphazardly (with respect to grain orientation) slab cut maple glued together will make for a very stable billet from which to make the neck blank.

Let me say a few more things about laminated neck blanks before proceeding. I will laminate up a neck blank for any of three reasons. The first as mentioned is in the case where the species of the wood I want to use doesn't have a history of being dead stable. There are ways you can get an idea of the relative stability of wood species, looking at how much they shrink when drying and how easy they are to hot bend, but for the most part I don't bother and simply err on the side of caution. If it isn't mahogany (or Spanish cedar for classical guitar necks) I laminate the neck blank. The second reason I'll laminate a neck blank is if the wood is not generally available quartersawn. And the last reason that I'll laminate is for looks. Necks can look fancier if made from laminated blanks.

Dimensioning the Stock

It is a lot easier to see what you are working with if you first surface the stock you are using S4S – planed smooth on the broad faces and with both edges ripped and planed straight and smooth. For a single neck I start with a board that is about 1/4" wider than the width of the fingerboard at the body join (FW); a bit (1/16") thicker than the thickness of the neck shaft at its thickest point (NT); and long enough to build the headstock, headstock side extensions, neck shaft and heel block, plus about 4" extra. To figure this length, start by adding together NL, DL and HL * 2, plus another 4" to give yourself a little breathing room. The reason to use two times the length of the headstock is to provide some material for the side extensions or “ears” of the headstock.

We're not done yet. Now we need to figure out how much stock we need for the pieces of the built-up heel. To determine the number of pieces needed to make the stacked heel block you can divide the length of the heel (LL) by the thickness of your stock and ignore any fractional part of the result. Multiply this number by 3" (or 4" if your neck will attach with a dovetail or straight tenon) and then add another inch for the saw kerfs. Now add this subtotal to the subtotal calculated above, and you have the length of stock you need for the entire neck blank.

A note here for folks that will use a planer to do the planing. If your planer tends to snipe the ends you'll need to add some extra length to deal with that.

Cutting the Stock into Major Pieces

The first cuts will cut off the pieces needed to make the stacked heel. These are each 3" (or 4") long. I use the table saw and miter gage with the fence set as a cutoff guide:

Next, a piece HL long is cut off the stock. This is the piece that will be used for the headstock ears, and it too is put aside for later.

The next step is to cut the piece for the headstock from the neck shaft with an angled cut so the headstock piece can be scarfed back onto the shaft piece. A mark is made at NL + 2" from the end of the stock. Then, using a protractor a line is drawn on the side of the stock at the mark and of angle HA such that the piece that will be the neck shaft will end up being longer than the length of the stock to the mark:

In this picture the line across the top of the stock was marked at NL + 2" from the right end of the stock, so the right hand piece will be the neck shaft. As you can see, due to the angle of the cut the neck shaft piece will be longer in length than to the mark.

Now the stock is cut on that line. This can be done with just about any tool – band saw, Japanese crosscut saw, etc. I do it on the table saw with a taper jig:

You can cut right on the line. There is still enough extra material on both ends so that we don't have to worry too much about critical dimensions at this point.

The next step is to plane down the thickness of the headstock piece. I try to make this piece about 1/16" thicker than its final thickness. The headstock on my finished instruments will be about 5/8" thick. The headplate and headstock veneers will be about 1/8" thick so the final thickness of the headstock itself will be about 1/2". So here I plane the headstock down to 1/16" over that, or 9/16". A planer makes short work of the job:

Note that the headstock should be planed with the cut face up.

Making the Scarf Joint

Even on the table saw with the taper jig the cut used to separate the neck shaft from the headstock will not be perfect and so the cut faces will have to be planed to flatten them and straighten them up. One way to do this that is simple and quick is to clamp the pieces together so the cut surfaces are aligned as best you can:

and then sand the faces flat and straight using the stationary disk sander:

Another way to smooth and straighten the joint surfaces is to back up the pieces with another piece of stock (the cut off that will be used for the headstock ears) and plane the surface:

However you do this, aim for a nice flat surface the edges of which are perpendicular to the sides of the stock. After the surfaces are flattened the headstock piece is flipped around and glued to the underside of the neck shaft piece. The orientation is like this:

Set up for gluing on a flat board. I use Melamine covered particle board (one brand name is Melguard) which is cheap, flat, readily available in home centers, and glue doesn't stick to the Melamine surfaces. Yeah, that's gen-u-ine wood-grained plastic in the next picture. But a regular flat board, well waxed or covered with waxed paper will work fine. First position the pieces on the board so the joint area and all of the headstock piece are completely on the board. Then clamp down the neck shaft piece to the board using two clamps:

Tighten the clamps. Then position the headstock piece and place a clamp right up against the butt end of the headstock piece and tighten it. This clamp is used as a stop so the headstock piece can't slip out when the joint is clamped.

Now spread glue on the face of the headstock piece to be glued. As usual with gluing and clamping, it is a good idea to do a dry run of all of this before actually committing to the glue.

Position the headstock piece into place. Then loosely position two clamps to hold the headstock piece onto the clamping board. Now two well waxed wood or plastic cauls are placed on both sides of the scarf joint and two clamps are used to clamp the joint. Tighten all four of these clamps together so that the headstock piece remains square to the clamping board and the joint is clamped square. Here's one look at the clamps:

Click to enlarge

and here's another looking from the top:

Click to enlarge

Let the glue dry for at least an hour before un-clamping. Now the top surface of the scarf joint and the sides need to be cleaned up as both will be gluing surfaces in the future. I clean up the sides with the hand plane:

and then run the top surface once over the jointer:

or if you don't have a jointer plane down the top surface flat with a plane. You'll remember that the headstock piece was planed 1/16" over its final thickness. All but about 1/64" of that will be taken off here. Note that in addition to cleaning up this surface for later gluing on of the headstock veneers you'll also want to make sure the edge of this face where it meets the top of the neck shaft is perpendicular. The headstock part of the neck blank is a few inches longer than the final headstock will be. I've made it longer on purpose, so that it could be surfaced on the jointer without danger of sniping it.

Marking Reference Lines

Now a reference line is scribed across the top surface of the neck at the start of the slope for the headstock. This line marks the forward edge of the headstock veneer, the back edge of the nut, and will be used as a reference for the ultimate length measurements for the neck blank.

Use a square to be sure it is perpendicular to the sides.

If the edge of the headstock surface is not quite straight then scribe this line a bit away from the edge and then plane the headstock surface to that line using a plane.

Now on the top surface of the shaft measure the thickness of the nut down from the line just scribed and scribe another line. This one marks the front of the nut and the end of the fingerboard.

Next measure down from the initial line NL, the length of the neck from the body join to the start of the headstock, and scribe another line here. This one marks the place on the neck where it will meet the body. If your neck will be attached to the body using a bolt-on butt joint then this line will represent the end of the neck, too.

If your neck will be attached to the body using a dovetail or straight mortise and tenon joint, measure down from body join line just scribed the depth of the tenon, DL, and scribe a line here. This line will represent the end of the neck if the neck will have a tenon.

Routing the Trussrod Slot

If your instrument will have a trussrod, now is a good time to route the channel for it, before we add the heel and the headstock ears.

Gluing up the Heel

The neck shaft is a bit longer than it will be ultimately and now it will be shortened closer to its final length. Extend the mark that shows the end of the neck (the body join mark or, if your neck will have a tenon, the end of the tenon) around to the underside of the neck. Make another mark approximately 1/2" further from the headstock end than this one and cut the neck off at this mark.

The heel pieces are stacked up and glued all at the same time, using a piece of Melamine covered board or other flat glue-proof surface to keep the pieces square to the neck shaft. You don't have to worry too much if all of the heel pieces are perfectly lined up with the end of the shaft at this point, but don't let then skew all over the place when gluing. Here's a picture of the clamping arrangement:

Click to enlarge

Trimming the Heel

The neck shaft and heel pieces are loosely clamped together, then the whole thing is clamped down on its side to the glue-proof board using a glue-proof caul on top. The reason the assembly was glued clamped to the board is to try to keep the sides of the heel block as close to perpendicular to the top surface of the neck as possible. We do this because we still need to do a number of operations that require that perpendicular relationship. But even careful clamping of a glued up stack like this will result in a bit of skewing:

At this point you'll want to square up one side of the heel so that it is perpendicular to the top surface of the neck. I do this by running the neck top down through the table saw, up against the fence to just trim the side of the heel, but this operation can be done with a stationary disk sander or with a plane just as well. No fine work is required here, just a bit of quick squaring up. Note: if you have a choice, trim the right side (when the neck is viewed headstock up and looking at the fingerboard surface) to square up the heel. In the picture above, this is the side which is up. Doing so will make it easier to cut out the horizontal profile of the heel on the bandsaw later.

If you've followed the measurement instructions for determining the number of heel pieces then the heel is either just the right length now or it is a little too long. Now is the time to trim the length of the heel and to add any heel cap and veneers that you want. Some measurement is now required to figure out how much to trim. I won't give any instructions here for that, but will point out that if your finished instrument will have the bottom of the heel flush with the back of the instrument that it is a good idea to make the heel a bit longer now than its finished length and to do the final trimming once the neck is on the instrument.

The instrument I am building here has a neck with a heel that falls a little shorter in length than the back of the guitar. It also has a heel cap and veneer, and the end of the heel is trimmed to a bit of a rakish angle that does not follow that of the dome of the back. I trim the heel on the table saw using the taper jig:

but other tools could certainly be used. After it is trimmed the cap and veneer are glued on and clamped.

So I don't have to square up the side of the heel again I use a heel cap that is a little bit narrower than the current width of the heel.

Cutting the Neck to Length

Now that the heel cap is on the neck can be cut to length at one of the lines previously marked. If the neck will attach to the body using a tenon of some sort then the next step is to cut off the excess length of the neck at the line which indicates the end of the tenon. If the neck attaches using a bolt-on butt joint, then it will be cut off at the line which marks the place where the neck will join the body.

I do this operation on the table saw, using the miter gage. On my flattop guitars the necks tilt back slightly to accommodate the slight doming of the tops, so that neck angle is set on the miter gage. Then I draw the line at which the saw blade will cut onto the saw table. A carpenter's level is held against the side of the blade and then the cut line is penciled onto the saw table:

Then the neck assembly is positioned on its side with the top surface against the miter gage and the scribed line on the top at which the neck will be cut is aligned with the pencil mark on the saw table:

and the end of the neck is trimmed to length. As you can see in the picture I use an 80 tooth fine crosscut blade, so the finish of the cut will be very smooth. This operation can be done using hand saw and plane, too. In this case the cut line would be extended down the sides of the heel, using a square or a protractor if there is to be a neck angle. The end of the neck is trimmed with the saw and then cleaned up with the plane. After the end of the neck is trimmed to length it looks like this:

The step I usually do next is to drill and install the threaded inserts that will be used to bolt the neck to the body. That process is described here. If your neck will attach with a dovetail or straight mortise and tenon, now is a good point at which to cut the tenon.

Cutting out the Horizontal Profile

As mentioned in the introduction, the process of building a neck has two major operations. The first is building up a blank that is the first order approximation of what the finished neck will look like, and the second is successively taking away wood from that blank to yield the final shape of the neck. Although we are not quite done with the building up part of the process we do the first of the stock removal operations at this point, while we still have a piece which will lay flat on its side.

The first step in cutting out the horizontal profile of the neck is transferring that profile to the side of the neck from the plan:

The picture shows just the heel portion of the profile penciled onto the blank. Now a large amount of the waste wood can be cut away using the band saw:

The line is further refined using a spindle sander (pictured) or a drill press mounted drum sander and coarse grit sleeves:

The end result looks like this, again just looking at the heel end of the neck:

Attaching the Headstock Ears

The last step in building the neck blank is attaching the headstock ears. As should be apparent, this is left until last because once the ears are attached the sides of the neck can no longer be used as reference surfaces, since the ears stick out farther than the rest of the neck blank. In previous steps we cut off a section of the stock for use in making the ears. Now that piece is planed to the thickness of the headstock and then ripped in half.

I use the same piece of Melamine board as a clamping surface for this operation as was used in previous operations. Glue is applied to the joint faces of the ears. The headstock and the two ears are clamped face down to the board using two hunks of glue-proof board as cauls. You don't have to be too careful about the location of the ears as they have been cut to the length of the headstock, but you should keep their ends somewhere between the line that represents the front edge of the headstock and the point on the finished headstock where the extra width (over that of the neck shaft) is needed. Once the headstock and ears are lightly clamped to the board, two clamps are placed to clamp the ears to the headstock. All clamps are tightened at the same time. The clamping arrangement looks like this:

Click to enlarge

I've aligned the mark indicating the front edge of the headstock with the right most edge of the gluing board. You can see the ends of the ear pieces are a little behind that edge.

After the glue dries the front and back faces of the headstock are flattened for subsequent operations. I usually do the front on the stationary belt sander:

but it can be done with a plane or with a large sanding block. This is a large surface that will receive the headplate and veneers so you'll want to get it nice and flat. If you use the belt sander be careful not to take too much material away, as this will move the line that represents the front edge of the headplate down the neck a bit. For the same reason it is a good idea to place the headstock front face on the belt sander top end first, and to bias the pressure of your hand on the headstock toward the top end and away from those scribed lines on the front of the neck. If you do manage to obliterate the reference line while sanding then re-scribe it now and also scribe a new line that represents the end of the fingerboard and the front edge of the nut.

The back surface is also roughly flattened at this time.

I'm doing this with a big sanding block. On this instrument the back of the headstock will not be covered with veneers so I'm not doing a really picky job of this at this time. But I do want to get it flat enough so that it will lie flat on a backer board when I'm drilling the tuning machine holes so that the holes don't get blown out the back surface of the headstock.

The “finished” blank looks like this:

ready for subsequent headplate and fingerboard attachment, cutting out of the vertical profiles, shaft carving, and cleaning up.

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