Mopus chapter 5: Quite the Body of Work

It certainly has been awhile since I posted a Mopus update. I had it in my head to wait until I was “done” with Mopus’ body – figuring it was “just” another chapter in the story much like the back or the sides. But that was way back in July, and I was imagining something like 4-6 weeks tops for me to get the body done. Well, it’s taken me a good bit more than that, and it was way more involved than I was thinking. Also, I do have a day job and all.  I had quite the adventure, one fraught with false starts, lengthy side excursions, little disasters, frustration, and even some spilled blood. Here is my tail.

Joining the Top

Way back in July, i.e. “in olden days”, this part of the adventure started by thicknessing and joining a book-matched set of sitka spruce plates. Just like the back, the top has to be perfectly joined. I made a “shooting board” to help with this, allowing me to use some large jointing planes and also some sandpaper glued to a marble strip to make a good joint.

This part took quite a bit of work, but I barely remember it now. After I got the joint perfect, I used the same jig as I used for the back to glue it up.

Now that I had the material for the top, it should be a simple matter to make it into one, right?

The Rosette Extravaganza

The next step was to install the rosette (the decorative ring around the sound hole). I had a standard rosette ready to go for this, but that would be way to easy. Much better to make my own from scratch, I figured. And so began an adventure that lasted for months. I looked at all sorts of rosette designs, and finally decided maybe I’d try something made from interesting looking wood, arranged radially. I hunted down a selection of various kinds of wood to try out, and decided I really liked the look of spalted maple.  Spalted wood has dark bands caused by a fungus. In other words, it’s rotten wood. It’s not very structurally sound, but it sure looks pretty.

My design involved piecing together segments arranged in a ring so that the dark bands radiated outwards. I made a simple cardboard template to find interesting places to cut the wood.

I’m going to spare you the long version of the tale of what happened next, because trust me, it’s long. The short version is that I tried many ways of forming a nice ring out of these pieces. I made all sorts of molds out of plastic and wood and tried too many things to even remember them all. At one point I actually had a full rosette. I was so proud of myself – took all sorts of photos – I imagined it installed in the guitar top in short order. Then I went to thin it down to the necessary thickness, and it fell to pieces. I tried to repair it several different ways, and had to accept that I had to start over. This whole thing happened AGAIN – I managed to finish a second full rosette – with all new wood – but the glue stuck to the mold, and it broke trying to remove it. During all this, I even cut myself several times with an Exacto knife, mostly as a result of being frustrated and impatient, and I still have a small scar to remind me not to do that again. Once again, back to the drawing board, but this time armed with some experience.  I made a different mold, designed to release the rosette when done. And I also used purfling strips between the segments to make stronger joints.

I actually like the look of using the purfling between the segments better than the original. So, lets just pretend I intended to do it this way all along.

The process of routing out the top for the rosette and cutting the sound hole went so smoothly, I don’t even have anything interesting to say about it. I soon had the rosette mounted in the top. The whole rosette thing took so long I almost forgot what I had to do next. Anyway, this is what it looked like at the time – I’m pretty pleased with it!

After all that, the rest should be pretty easy, right?

The Soundboard Bracing

I was finally on to the bracing. What I had to work with is a few hunks of sitka spruce which I cut into strips and gradually formed into braces.  Even though there were a bunch of fun steps here – spanning multiple weekends – the whole thing actually went down pretty smoothly. Here’s a picture of using the go-bar deck to glue in the finger braces.

I spent quality time “voicing” the top – i.e. making it sound like a drum when you hold and tap it a certain way. This process is called making the top “responsive”. Lots of experience is required to know what a “responsive” top should sound like at this point. Only after you play the guitar do you know if you got it right or not. I did the best I could, but I do sense the top is stiffer and not as responsive as my first guitar, which if true will mean the next time I’ll know better. Anyway we shall see what it sounds like when I’m done.

It is tradition to sign the soundboard – so I put my John Hancock on the thing.  Here it is ready to be mounted on the body.

At this point I figured I was almost done. I just have to glue the top to the back, and I can move on to the neck, right?

Closing the Box

Before I glued the top to the body, there was one little detail to finish up on the inside – a label. I figured if I was going to spend a whole year making a guitar named Mopus, it at least needed a custom label. So I spent some time designing a label just for this guitar. It almost looks official!

Now for fitting the top to the body – chiseling notches where the braces stick through the sides. I’ve done this several times by now, so it doesn’t seem like a big deal to me anymore. After fussing with the fit for awhile, I glued the top using the go-bar deck with the top facing down on the radius dish.

And now Mopus had a body! Well, sort of… but surely we’re almost done with this, right?

The Binding Machine

All I need to do now is put some nice binding around the edges. I did this before, with plastic bindings, and although it scared the hell out of me at the time, I got it done. So I’ll just do the same thing again and move on. Well, not so fast. First I resurrected the binding jig I made for the first guitar – back when I was just a baby luthier.

It’s supposed to hold the router perfectly in alignment with the sides of the guitar, so that I can cut nice even channels for the binding strips. What I quickly found out, after several test runs, is that putting in wooden (in this case curly maple) binding is MUCH more complicated that the plastic bindings I used the first time. There is no margin for error now, and believe me, the first time there was plenty of error. So before I could put in the bindings I had to make a real “binding machine”, a jig to help make accurate binding channels. Yes, I could buy one, but they are silly expensive for a tool you use for maybe 10 minutes on each guitar. So I put the guitar building on hold, and embarked on a side project to make my own binding machine.

What you need is a way of holding the guitar in such a way that the guitar edge is level all the way around. This is challenging, because both the top and bottom are curved. A common and simple solution is to make a cradle with adjustable posts to support the guitar, so that’s what I did. So far so good.

The more difficult challenge is to make something to hold the router that only moves vertically.  That way, the router bit and the resulting binding channels are always parallel to the guitar sides. After looking a many possible designs, I went for a relatively simple approach of using ball bearing drawer slides to make a sort of vertical drawer with a shelf for the router to sit on.

Also, the router has to ride along just the very edge of the guitar, otherwise the depth of the cut will be uneven due to the curvature of the top and bottom. So I made a “doughnut” ring out of maple.  I cut it to a rough circle and glued a dowel into the center.

The dowel is so that I could chuck it into a hand drill and form the doughnut by spinning it against a belt sander. And that worked great. It did take some trial and error – in fact I had to make a second one. I did the final shaping with it chucked into the drill press, using fine sandpaper to get it smooth. I want it to smoothly glide on the edge of the guitar, so it has to have almost no friction. With some work and polishing it looked pretty good! OK, I suppose looks are besides the point, but still…

I also rigged up a counterweight to make the platform with router attached raise and lower easily with just one finger. There’s a pulley mounted at the top, and and a cable connects the platform up to and around the pulley to a small sack filled with heavy items in the back. I just played with what I put in the sack until it felt balanced.

After some shellac and some fine tuning, I have a binding machine! With the exception of the drawer slides and the pulley, I already had all the parts for this laying around, in the end saving hundreds of dollars. And now I have it, so I can use it for other guitars in the future.

At long last, I was now ready to cut the binding channels and get the body done. Surely this part will be easy, right?

The Binding Channels

After spending all that time designing a building a binding machine, the actual use was a bit anti-climatic. In reality it took maybe 20 minutes to actually cut the binding channels, and most of that was setting up the depth of the router on scrap wood. I had done many tests before starting so that there would be no surprises, and thankfully there were none.

And now for the simple matter of installing the binding. Or not.

Bending the Binding

With the plastic binding you see on nearly every guitar, you just push the binding into shape as you glue. No wonder it’s so commonly used. But silly me, I wanted to use curly maple. The cool shiny ripples in curly maple are caused by end grain, which in English translates into “very easy to break”. I had 6 pieces of binding ready and I only needed 4, so I had room for error, or so I thought.

With wood binding you have to first bend it into shape. I began by hand bending the sides using the bending iron, and I thought the first one came out pretty well, so I was feeling confident. The next one snapped in two almost immediately. And so did the one after that.  I went veeerrry slowly after that, and with much stress got 4 bindings bent. I even went the extra step of clamping them into the inside of the guitar form, wetting them and then heating them further with a heat gun and letting them sit overnight to make a snug fit. I was feeling really good. Will I ever learn?

After I removed them from the form, I realized to my horror that they were badly scorched / burnt in several places from the heating iron. For a time I thought I could sand out the burn marks, but no. I had no choice but to get more binding material and go to plan B, whatever that was.

While waiting for the replacement bindings to arrive, I figured maybe plan B would be to steam the bindings. So I built a steam box from a PVC pipe. I figured I could use the coffee machine milk frothing trick I did when I did the neck reset on the first guitar. I knew I saved that setup for a reason.

Well it looked cool anyways. After steaming the bindings, I found they were even more brittle than before! Apparently this is a well known annoyance about using curly maple, known by everyone but me. So it’s on to plan C.

The next idea was to press the bindings into shape with a form, a heat gun, and some clamps. The idea was to wrap the bindings in aluminum foil with a touch of moisture, and have a form rimmed with aluminum tape that I could heat more evenly versus using a bending iron. So I made a form to do this, which I wound up having to modify at least three times.

Although it eventually worked, a successful technique was not something I arrived at quickly. In fact, I’m humbled to say that I broke at least 10 additional binding strips before I had a set of 4 that I could use. Clearly, the next time I do this, I’m going for plan D, which is to use heating blankets and a bending machine (which I will also use to bend the sides) – just like the big boys do. That’s something I can obsess about in the future, but for now I’m really on to the final stretch for Mopus’ body.

Installing the Binding

Gluing in the binding also presents challenges, but now I was back to something I sort of did once before (although with plastic last time). But I already had the experience of using tape to hold the binding in place, and then using a really really long rubber band to hog tie the guitar and apply good even clamping pressure all the way around. I can be a little stressful, because you’re fighting the clock as the glue sets, so I put on some Chopin to calm me down, and went to work.

The End (of this chapter)

And so,  after many adventures over hill and dale, after frustration and injury, after fighting off orcs, trolls, and a balrog, and with absolutely no help at all from from wizards or eagles, I have a body for Mopus. Now I’m on to making the neck. I’m sure that will be easy, right?