Guitar Build 7: Fretboard Inlays

FeaturedGuitar Build 7: Fretboard Inlays

[From the build on 1/5/2017] This week we worked more as a team and began concentrated time on our fretboards.

Using the acrylic template, Ryan drew a line along the front edge of the bodies where the neck will join. Here we differ slightly from the standard Les Paul, in which the tangent to the top curve is vertical where it joins the neck. Our curve curls under just a bit, giving the body a distinctive look. That also means a different angle for the front edge. Ryan cut on the bandsaw then finished on a belt sander. (Thanks Ryan!)img_4224

Meanwhile, Ted took the mahogany stock we used for our bodies to cut blanks for our necks—standard face joint, plane, edge joint, rip cut prep. He also ripped a trough precisely in the center that will hold the truss rod.

Most of the night was consumed with fretboards. Rather than center dots, Ted set us up for edge inserts at all the standard frets (3, 5, 7, 9, 12, 15, 17, and 19), with a double insert at the 12. We started by marking the cut lines, then moved to the drill press where a bit exactly matching the inlays was installed. The depth of this cut is critical—it must be deep enough so that when the (fretboard and fret markers) are sanded we don’t sand through the inlay on the edge, but not so deep that the cut exceeds the height of the inlay. As always, set up is crucial.

After making the cuts, we rounded the corners of the inlay pieces so they would fit exactly into the routed grooves in the fretboard. To do this, we simply rounded them with sandpaper by hand. The inlay is paoa abalone, but I tried not to go for the really colorful parts so that the marker would still have significant contrast against the ebony fretboard.

Next, the Superglue. I hate Superglue! Commitment is hard enough, but commit with a deadline in 45 seconds is the pits. We used 20 Superglue, applied with a toothpick to get it into the groove, then set the inlay pieces in one by one. And that’s where we left it for the night.

Guitar Build 6: The Magic 4 Degrees

FeaturedGuitar Build 6: The Magic 4 Degrees

I am behind 4 weeks now on blogging the build, so this post covers the December 29, 2016 session.

We had two tasks to accomplish this first week. First was to skim the front of our tops at a 4 degree angle to allow the neck to join the body at just the right angle. Apparently this magic angle comes from Les Pauls made between 1954 and the late 1960s, when they were made in Kalamazoo, Michigan. Afterward, the neck-to-body angle was increased to 5 degrees and more (all according to “How to Make Your Electric Guitar Play Great!” by Dan Erlewine).

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My son Charles setting the neck to body angle at precisely 4 degrees.

We mounted the bodies on a large metalworking router that features a table that can be moved very precisely. So, instead of moving the router bit through the workpiece, we move the workpiece under the bit for more control. As with so many operations in woodworking, the setup is the key. Once the angle is set and the workpiece secured, the rest is pretty easy.

The second task was to cut a wide groove in the top to receive the neck. This is one of several operations that must be done precisely, because lack of fit where the neck joins the body affects the sound. So of course, I goofed this up! Somehow I moved the piece too far into the bit and I carved out too much of the maple top (see photo). Alas, I lucked out again because this part of the top will be cut out for the pickups anyway. As they say, “I’d rather be lucky than good.” Actually, I’d like to be good too.

Guitar Build 5: Bugs in Wood

FeaturedGuitar Build 5: Bugs in Wood

Engineers are frequently accused of seeing everything as black or white, which is one reason woodworking is good for my soul. Imperfections in materials and overcoming mistakes are what it’s all about.

This week I had to deal with another misstep, this time on my top. We began the night planing our maple tops to thickness (5/8″). As always, we jointed one face, then used the planer and then the belt sanding planer (a monster!) to get to precise thickness. At this point, the top is pretty smooth and showing off its curly grain self. The process of exposing beautiful wood grain is something like sculpture—the beauty is in there somewhere, we just need to take away what’s hiding it.

After planing away a fair bit of the top, it turns out that the insect damage had “moved” toward the center of the guitar. As I said in my first post, I took a gamble on this piece of maple, knowing that the bug damage was close to the edge of the body. Alas, it had migrated to the top and bottom edges (see photo).

We have two ways forward. The binding will partially cover some of this scar, and the remaining should be hidden in the dark brown outer edge of a tobacco sunburst. Ted offered a second way: we could modify the shape slightly to cut out these imperfections (top and bottom). Messing with the design of the master makes me nervous!

After drilling registration holes with the same template used for the body, we glued top to body. I discovered another interesting part of electric guitars here—one of the cavities has no electronics and is completely devoted to resonance! I had no idea a “solid body” guitar had such a cavity. There you go.

We finished the night bringing the edges of the fretboard into line and at the proper width. Because of a bandsaw error, mine had to be brought in a little under width. We’ll compensate for this error with a touch of extra binding.

While we were working on fretboards, Ted cut some 1/8″ maple strips for edge binding the fretboards. We glued these strips to a mahogany veneer, so the fretboard will have an “ebony to mahogany to maple” edge. Should be nice.

Production Notes

  • Avoid maple tops with bug damage 🙂
  • Dry fit everything before gluing! I got lucky on the top to body glue up, which I did without dry fitting.
  • A good, straight edge on the sides of the fretboard is more important than the width. Compensate for imperfections in width with the binding.
  • Glue will seep through a veneer, so go light on the glue and make sure to put down wax paper first.
  • Be careful reading calipers! It is very easy to misread this device.

 

 

Guitar Build 4: The mathematics of fretboards

FeaturedGuitar Build 4: The mathematics of fretboards

Apparently, we have Pythagoras to thank for the musical scale. Using a device called the monochord, he was the first to notice the relationship between string length and octaves—namely, that halving the length of a string produces the same note one octave higher. An octave is twice the frequency of the original note (ratio 2:1).

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Fretboard before shaping. The cut at the bottom will be the nut, or the zero fret.

He also noticed that certain notes sound good together, a concept called consonance. For example, the note we call E sounds good with A. E is created from A (as its fifth) with the string ratio 3:2. A has frequency f=110 cycles per second (cps), so E has frequency \frac{3}{2}f =165 cps. D is created from A with ratio 4:3 (as its fourth) with frequency \frac{4}{3}f. And so on. Not all simple ratios produce consonance with A (5:4 does not), but using fourths and fifths around A, D, and E, we can produce a pentatonic scale.

 

At some point we decided 12 was the right number of notes, so the task was to produce a set of 11 frequencies between f and 2f that “sounded right.” The search eventually produced “the tempered scale” having the property f(n)=a f(n-1). This is a recursion, so f(2) = a f(1); f(3) = a f(2) = a^2f(1); f(4) = a f(3) = a^3f(1); and so on until we get f(12) = a^{12}f(1). But we also know f(12)=2f(1), so 2f(1) = a^{12}f(1) and our constant

a = \sqrt[\leftroot{-2}\uproot{3}12]{2} \approx 1.059463094359295264561825294946341700779204317494185628559.

(Much of the above comes from a nice article at Noyce Guitars.)

We are interested in the distance between frets on a fretboard, or to avoid accumulating errors, the distance from the nut to a particular fret. If the length of the string is s, the distance to the nth fret has the formula:

d[s,n]=s-\frac{s}{2^{n/12}}.

Notice that for the 12th fret,

2^{12/12}=2,

and we divide the string in half, as expected. See this nice article for a fret spacing calculator. So there we have it, a nice way to calculate the distance from the nut to each fret. Because cuts this precise would have taken so much time and because they are so critical to the sound, we ordered our fretboards from a guitar parts distributor.

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Maple top after glue up. Glue line is visible across the middle.

This week we glued up our maple tops in the same way we glued the two piece mahogany backs. Both faces had been planed, so we had only to joint one side of each piece and then glue and clamp.

Next we turned to the fretboard. After marking the width at the zero and 16th frets last week, we were ready to mark the cut lines and trim them on the band saw, leaving about 1/8th inch room to bring them down to exact shape with the bench plane. For the planing, we are using Ted’s “shooting board,” which is a jig that allows use of the plane as an edge jointer. I finished the night with my fretboard edges straightened, but I will have to remove more stock next week to bring it to the right width. We are checking the width with calipers, because width at the 16th fret is critical for the guitar’s cutaway to fair into the neck properly.

Production Notes

  • When cutting the fretboard on the bandsaw, leave the cut proud! You’ll take this off with the bench plane anyway.
  • Razor sharp and tuned plane is essential for every woodworking operation.
  • Need to build a shooting board for fretboard trimming.
Featured

Guitar Build 3: Routing the body

One of the fun parts of a project like this is being made to think about things I just never noticed in the past. For example, why does a Fender Stratocaster have a large faceplate, when the Gibson Les Paul does not? Answer: the Strat has a one piece body, so the only way to get the electronics inside is to rout out the face, which leaves a hole that must be covered. The Strat also has a cavity in the back for tremolo springs.

Stevie Ray Vaughan's Stratocaster "Number One." Notice the large faceplate, which allows a single piece maple body.
Stevie Ray Vaughan’s Stratocaster “Number One.” Notice the large faceplate, which allows a single piece maple body (source: srvguitars.com).
Robben Ford's '99 Les Paul. The curly maple top is glued on to the back; therefore, no need for a face plate.
Robben Ford’s ’99 Les Paul. The curly maple top is glued on to the back; therefore, no need for a face plate. (I plan to finish my guitar with a tobacco sunburst slightly darker than this one.) Source: lespaulforum.com

To allow for a beautiful wooden top requires a two piece body (not counting the two pieces that make up each piece of the two pieces!). As I covered in a previous post, we’re making a mahogany body (the back) and a curly maple top.

So, this past Thursday we spent most of our time on routing cavities into the backs of our guitars for electronics. The front side of the back, which will be covered with the maple top, has two large cavities and a channel for the selector switch. The back side of the back also has a cavity to allow for the control knobs.

Jointing the body on Ted's 16" jointer. You can't do this at home.
Jointing the body on Ted’s 16″ jointer. You can’t do this at home.

After being glued up last week, the two piece mahogany backs needed to be prepared and brought to proper thickness (1 3/4″). As always, we began by jointing one side, which is a “you can’t do this at home” operation. My jointer at home can handle stock 4″ wide, but our bodies are 14″ or so. Not to worry: Ted’s industrial strength jointer handles 16″ stock!

Next, we brought the back to approximately the right thickness on the planer. Most planers for home use are 13″, I think, so this operation requires a shop as well. Ted’s planer is 20″. After planing, we brought the piece to just the right thickness with a huge belt sander that operates just like a planer. This machine is impressive.

Removing stock before routing.
Removing stock before routing.

At this point, we drilled “registration holes” to which we will affix templates for the routing and perhaps other things. Instead of using the router to remove all the stock, we used a Forstner bit to remove most of the stock, then finished the job with an inverted router. This is where I made my first blunder:  When using a router, the direction you push the stock is critical.  It turns out I was supposed to rotate the piece counter-clockwise when the router is inverted and cutting an inside edge (see this helpful Woodcraft article). I rotated the wrong way, causing the bit to “jump,” and somehow the bit removed stock outside the template (it probably moved). Ted is pretty sure the back plate will cover the goof. We shall see.

Cavities for electronics. My router blunder is visible on the inside lip of the bottom right cavity. Sigh....
Cavities for electronics. My router blunder is visible on the inside lip of the bottom right cavity. Sigh….

Finally, we planed off the burn marks from our maple tops, and then bookmatched them for the best look. Can’t wait to see these babies finished!

My top. Note the insect marks on top and bottom. These should be outside the cut of the body, and so go to waste.
My top. Note the insect marks on top and bottom. These should be outside the cut of the body, and so go to waste.

Production Notes

  • Prepare the mahogany back in the usual way. Face jointing requires a 16″ jointer. Planing requires a 20″ planer.
  • Placement of registration holes is critical.
  • On an inverted router, rotate the piece counter-clockwise on an inside cut! Read the Woodcraft article before proceeding—don’t goof this up!