Sunday, January 20, 2002

Mandolin #1: Carving

Carving the top and back of the mandolin was one of the steps that caused me the most trepidation. I had read about people carving with hand chisels, power chisels (like a Dremel), planes, and even sanding discs mounted in drill presses but was not sure whether to run out and buy and special tools until I knew how I wanted to proceed.

Carving the Top
Fortunately, the MacRostie video at least got me started on the process and I refined my approach as I went. The first step in carving the top is to establish the recurve on the outside. I had decided that one special tool sounded worthwhile and bought a Sloane Violin Plane from StewMac. This tiny plane has a convex bottom so it can carve along a curve and takes only a sliver of wood with each pass. You can see this little gold plane in the pictures to the left. Essential to using this little tool is careful understanding of how to carve with the grain of the wood (different for the spruce top and the maple back) as described in the MacRostie video. You can also see my carving set up consisting of the top clamped at the neck and tail to some blocks and additional blocks under the sides for support.

After systematically widening and deepening the recurve and starting to blend it to match the center of machined top, I brought out the random orbital sander to finish the job. With the top properly clamped and supported and a relatively coarse sand paper, the orbital sander was definitely the the way to go to blend between the recurve and the top and even to deepen (carefully) and even out the recurve. I used the sander much more on the inside of the top and the back once I figured this out.

Top carving setup 2 Top carving setup Carving the top recurve First round of top recurve carving

Opening the Scroll
Wait a second, I just spent all that time working on carving the top to precise curvatures and now you want me to cut into my work with a saw? What if the blade slips and I hack off the scroll? All my work on the top will be wasted. Well, it turns out this is a situation that repeats itself multiple times in mandolin building and the best one can do is to arrange the building process so that the more risky operations to a certain piece come before the more complex ones. Thus, if a risky operation goes south, it's easier (emotionally) to scrap the piece and start over. Do I seem sensitive about this? Well, read on (with special attention to the Assembly section).

In my effort to minimize the chances of a slip of the saw, I set to work opening the scroll with a chisel. As you can see from the picture, it started off looking pretty ugly, but it quickly opened up enough that I could use some 60 grit adhesive sandpaper on strips of plastic as well as some needle files to expand and smooth things. When it's all done, it looks pretty good (despite the picture quality).

Cutting the scroll Opened scroll 2 Opening the scroll

Carving the Scroll
I was very nervous to find that the next step was carving the scroll. To me, the scroll is the most elegant part of an f-style mandolin and is one of the most striking features on any musical instrument. It's rise above the sides on top and back can make it the thickest part of the mandolin and gives it a very impressive feeling. I've heard people say that the scroll ridge actually provides strength to the top. In any case, I often notice how smoothly the ridge fades into the top and back and subtly suggests the recurve that continues around the body.

After making a template from the blueprint (using my trusty clear plastic) and drilling holes along the scroll ridge (in the template not the mandolin, genius), I could make pencil marks in the drilled holes to show the ridge pattern. Then, with my curved gouge, I worked in both directions from the ridge line until I had a nice pronounced ridge. Next, I attempted to smooth out the gouge marks with some sandpaper on a plastic tube.

I knew I wanted to make the scroll button as pronounced as possible so I tried to make the slope from the ridge to the inside of the scroll as steep as I could. I also wanted to maximize the rise of the top above the sides as the scroll curved around near the neck so I made this slope more gradual while trying to match it to the inside slope. I was not sure how the carving of the point where the ridge comes into the button and where the inner slope rises up to the button level would affect the binding that would have to fit in there later, but... that's later.

Top Scroll Outline 2Carving the scroll   Carving the scroll 2Carved scroll 3 Carved scroll 2

Graduating the Top
The next step was to hollow out the underside of the top to match the contours I had carved on the outside. In order to be sure of the amount of wood to remove at each point, some kind of measuring device was necessary. This was one of those cases where I was not sure whether to run out and buy a special tool (a deep throat thickness caliper from StewMac) or to try to make due. After having my finger on the order button several times for this $140 item, I came across a few descriptions of homemade calipers and coincidently a perfect dial gauge at Sears. After some experimentation with the best thickness to minimize flex, I cut a wood frame from some oak and mounted the dial gauge. One key design feature include the need for the bottom of the "feeler" to be small enough to drop into holes left by a gouge to give a correct reading (I replaced the orange cap seen in the picture with a smaller black one). I also made this bottom feeler adjustable up and down so the whole device can be calibrated.

Homemade thickness caliper 2 Homemade thickness caliper Using the caliper

With my new caliper, it was clear that I had a fair amount of wood (of course we're still talking in thousandths of and inch) to remove from the inside of the top. With this in mind, I abandoned my delicate violin planer in favor of the gouge that had worked so well carving the scroll. After tracing the inside of the rim onto the underside of the top, I started working around the outside to establish the flat border that would glue to the rim. I then moved towards the center removing material. You can see from the pictures how important it is to carve in the direction of the wood grain. With the gouge, there's definitely a risk of it "diving" on you and leaving a much deeper hole than desired. This happened to me a few times. In some cases I could even out the areas around the hole and end up with a consistent thickness. In other cases, I marked the area and stayed clear figuring that a tiny area (smaller than a pea) that was too thin would not be a problem.

By the way, I chose to hollow out the inside of the scroll on the theory that it might lighten the instrument slightly and increase the volume inside the body. I think the jury is still out as to whether this step has any effect but it was easy to do.

 Top inside carving Top inside carving 2

As more material was removed from the top, I frequently checked the top thickness using the caliper. Clamping the top up on the blocks allows me to get the caliper in to measure easily. As I got closer to the correct measurements, I took the whole setup outside and continued with the random orbital sander. With 60 or 80 grit paper, the sander removes a significant amount of wood and the round sanding discs make it easy to shape along the curves of the outline of the body. I had a few scares when areas I thought I'd measured correctly turned out to be thinner than I'd thought because the frame of my caliper had been flexing under its own weight when I held it from anywhere other than the handle. As a result, I was so nervous about making the top too thin that I ended up chickening out and quitting before all the gouge marks were removed. As it turns out, I've since heard that the measurements on the StewMac plan are considered by some to be "beefy" and that I probably would have been okay evening those areas out even if the result was thinner than indicated on the blueprint. Next time, I think I'll use the orbital sander even earlier and avoid the issue. In any case, I'm sure some one will open up Coydog #1 in 200 years and speculate that its creator (a genius no doubt) carefully gouged these "sound nooks" into the underside of top, each perfectly positioned to intensify a specific tonal objective.

Carving the Back
With the back, I went right for the gouge to create the recurve then promptly to the orbital sander to smooth out the transition to the center. In opening the scroll on the back, I was buoyed by my now extensive instrument building experience and went for the coping saw with good results despite anxious moments watching the scroll flex with each stroke. The fine shaping was still done with my plastic sanding strips and needle files. Carving the scroll went similarly to on the top. Graduating the back was done with the gauge and then a healthy dose of the orbital sander. There is a significant amount of material in the back to support the neck joint. The back comes to what looks like the flattened hull of a boat as it approaches the neck block.

Checking top thickness Finished top

Index of Project

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