Kit explanation

A good friend of mine (Suave) asked for some detail that separated this kit build from simply building from scratch. After reflection I realized that the aspects of the kit might not be clear to everyone from the descriptions so far, so I sent him this:

I guess I should have spent some time illustrating the kit itself. The kit came with all the wood, the fret wire, the fretboard side and top dots, and the nut and bridge material. The top was bookmatched, properly thicknessed, and had the soundhole cut. The back was also bookmatched. The kerfing was precut and prekerfed, although there were four pieces each of which was far too long and had to be properly trimmed. The braces were provided, properly thicknessed in cross section but requiring shaping both to form the curve of the top and the shape of the side of the braces away from the top or bottom (the manufacturer provided a long narrow piece of plywood that, when clamped to the table at one end and blocked up at the other end, will form the curve necessary for the curvature of the top). I do have to learn to fret an instrument, though - but they provided enough waste fingerboard with fret slots cut into it that you can practice this before going big time, and they also included extra fretwire. Critically, the sides were prebent. This is probably the biggest advantage of the kit since it meant that I would not have to learn to bend sides in concert with everything else (though it should be noted that I have some limited experience with bending wood and it is not that difficult to do - though my experience is not to the level of tolerance required for instrument building). I plan to bend them myself the next time.

Interestingly, not included were a tailpiece (mandolins typically use trapeze-type tailpieces) or tuning machines. I will buy these this spring after completing the instrument. I think the project is going fairly well, although it appears that the mandolin will be slightly nonsymmetrical about the axis of the neck - the sides might not have been exactly the same length and that seems to have resulted in a slight lopsidedness favoring the side that will be "up" when I play it. I don't know that it will be obvious to anyone but me (and, now, you) or that this will be the most out-of-whack thing about it in the long run. So far I am pleased.

I see your point - most of the tough stuff was left for me to do - but just gluing together a pretty much already built instrument would not be all that rewarding, I guess. This has been very rewarding so far. Believe it or not they actually have a kit with less stuff done for you. You have to bend the sides and glue up both the top and the back in that one. I might try that one next. In fact, I almost certainly will.

Kerfing for back

On Monday I took the mandolin out of the clamps (err... clothespins) and examined my work. Here is the result of the glue-up of the kerfing for the top of the mandolin:


Here I'll take a moment to once again try to explain kerfing. I now have a couple of good examples of what it looks like in the field.




See how the kerfs in the wood (the word kerf refers to the bit of wood removed by the passing of a saw blade, so here they are the notches in the wood) allow the wood to bend smoothly while still maintaining a nice bit of glue surface on top?




Here we have two closeup details of what the kerfing looks like. Notice how the kerfs close slightly on inside curves, allowing the wood to bend smoothly.






Finally, I have a closeup of the kerfing in the clamps, showing the small amount I left the kerfing proud of the sides during the glue-up. The instructions say to make this small reveal about 1/32". No idea how close I am to that but it looks fairly good, anyway.





These last two pictures are of the glue-up underway, showing how I laid out the kerfing on the side while clamping. Also shown is a photo of the back with all clamps in place.






After this was done I had some time before my wife and boy came home. The next step in the instructions is to layout the braces on the top and back. However, it recommends cutting up the pattern to make this easier. I'm an engineer and I hate working on an original - it makes it impossible to revert - so I decided to take the pattern/drawing in to the office and make a couple of copies before cutting anything up. The next step after the layout step is to cut the soundhole patch. This step does not rely on the layout on the top so I decided to do this step instead.

The soundhole patch is a very thin piece of wood that reinforces the top at the soundhole. The top is made of bookmatched spruce - which essentially means that it is made of two identical pieces with a joint running from the tailpiece to the neck - and the soundhole patch strengthens the top in the area where the material was removed to make the soundhole. The wood is very thin - almost a veneer, really - and the intention is for the soundhole patch to have its grain run perpendicular to the grain of the top. It's trapezoidal and because the wood is very thin I cut it with my Exacto knife and a straightedge. A few moments of layout and the cuts were made.


The photo on the left shows the layout of the soundhole patch cuts, including the patch itself, the framing square I am using as a straightedge, and the drawing/pattern. The one to the right shows the soundhole patch after trimming with the straightedge and the Exacto knife. I should also take a moment to apologize for the incredibly ugly cutting mat. Darn you, Wal Mart!!!



The final image of the day shows the drawing/pattern, the soundhole patch, and the top blank. The next step, probably on Wednesday, will be to transfer the brace locations and commence to shaping the braces, and to glue the soundhole patch onto the top.

Return to the shop

I finally got to return to the shop today. As promised, today's steps were exciting ones that really moved things in the right direction. I prepared the "mold" for the mandolin, and also glued up the kerfing. These are the biggest steps I've taken yet towards actually finishing the mandolin (which is still a LONG way off).

Along the way, a few explanations.

First, the mold. Stringed instruments are constructed of wood (most of the time, and this one is in that class). Wood has a tendency to deflect under pressure - that is, it bends when you pick it up or work on it. Since the sides of the instrument are made of very thin wood, they will tend to deflect quite a bit while you are attaching the kerfing and the top and bottom. Of course, once the top or bottom have been added to the instrument the mandolin will be fairly stiff, but until then you want to keep the instrument in the same shape as the final product as far as possible because every part added will tend to stiffen it, and if parts are added while the sides are deformed due to handling they will tend to cause a system-wide deformation in the final product. So typically builders use a form to ensure that the instrument keeps true to its final shape wile being worked upon. These molds take many shapes and forms - molds for guitars are frequently made of wood and form the outside of the instrument. My kit calls for a cardboard mold that fits inside the instrument as shown here.

The process started with selecting a piece of cardboard that the pattern would fit onto (the kit says to use the "included" cardboard but my kit did not include a piece - fortunately the lid of the shipping box for the kit was large enough to cut a piece out of). I then used a glue stick to adhere the paper pattern to the cardboard and, using an Exacto knife with a fine-tipped blade and a straightedge, I cut the mold out by following the lines (the yellow-green thing in the photos is the cutting mat). First I made a series of straight cuts to remove the bulk of the material, staying just outside of the lines and cutting the waste away. Having done that I cut the pattern out by carefully following the lines with the Exacto knife. I did this in small sections by making cuts perpendicular to the cut line out to the edge of the waste area and then removing the waste by cutting along the cut lines. Here's the final product of this process:

You can see some of the waste pieces lying off to the left and the Exacto knife I used to the right in this photo.

Once the mold was in place it was time to add the kerfing. Kerfing is actually a process by which a series of cuts are made parallel (usually) to one another in a piece of wood to make it easier to bend the wood. In stringed instruments the work also refers to the small pieces of wood, often triangular in section, which are used to glue the top and back onto an instrument. These pieces are kerfed to make them easier to bend into shape. The purpose of kerfing is simple: the sides of the instrument are far too thin to offer enough glue surface to make a secure joint between the top and side. The kerfing is securely glued to the sides and then glued to the top, offering enough glue surface to make a strong joint. My instructions say to use clothespins for clamps since they can be placed very closely together along the sides to ensure even clamping pressure. They also recommend wrapping the clothespins with rubberbands if they have weak clamping force. My clothespins, bought at Wal Mart, had terrible clamping force, so I did this. I started by dry fitting the kerfing to the mandolin to size it and to determine how many clothespins I would need. I fit 23 pins in the dry fit, so I took a few minutes and wrapped 23 pins with rubber bands. I then spread glue onto the first piece of kerfing and clamped it in place using the prepared pins. It turns out that because the pins are significantly wider when wrapped with rubber bands I only used 20 of them. To the left is the first piece of kerfing glued in place. You then repeat the process with the second side (shown on the right).

One final note: the instructions tell you to leave the kerfing about 1/32" above the sides. This will be sanded down at a later moment in the proper shape for the slight bow curve of the top. I tried to do this, and the detail below is the result.

A brief respite

I apologize but with the Christmas season upon us my progress has been entirely stopped. I will resume working on the mandolin (and the next step is an exciting one!) shortly after Christmas.

Neck bolt hole

I went out to the shop today to accomplish several non-mandolin related items while my wife and son were napping. While out there I took a moment to drill the neck bolt hole. The instructions recommend just turning the bit with your hands using the predrilled neck block as a guide since a drill is unlikely to fit into the glued-up mandolin sides. I happen to have a right-angle drill, so I could have used a power drill for this purpose. However, upon reflection I decided that the bolt hole was being drilled through the very thin sides and drilling by hand might do somewhat less damage to the sides than drilling with a power drill would. I resolved, then, to twist the bit in by hand. First, of course, I had to go to the hardware store to buy the bit (it's a 9/32" bit and such a size is not a part of any set of bits I currently own). I twisted it in by hand, which turned out to be easier than I expected, but of course it bound when it reached the outside of the wood. I then turned it once with a pair of pliers to complete the hole. To ensure that the hole was clean I then retwisted the bit in by hand from the outside.

To add ridiculousness to the situation I did not have my digital camera at hand, and so the photo of the completed hole was taken with a cell phone.

Good news

I've been down for several days because the weather turned colder recently and as a bonus my kerosene heater took a hiatus. I ordered new wicks for it, which I received and installed today (what a pain in the neck!) so I hope to be working again tomorrow. While I was out there working on the wick I went and looked at the blocks and sides I glued up a few days ago today in order to satisfy myself regarding the issue with the sides being wider than the blocks are thick. To be honest I was worried that I had a major mess up on my hands because I failed to notice the problem until after the neck block was glued in. When I noticed I was at least smart enough to keep both blocks level with the same edge of the sides. However, the bolt hole for the neck (which is a bolt-on neck) is eccentric relative to the thickness of the neck block (it's closer to the back side of the block) and I didn't know whether I had set both blocks level with the top or back edge of the sides.

As it turns out I set them level to the top edge.

This is unbeliveably good for several reasons. First it means that the neck will fit as it sits right now. I was worried that I would have to do alot of adjusting to make this fit work out. Second, the back really isn't under any tension when the mandolin is strung up. However, the front bears the loads from the strings. I therefore want the front to be completely glued to the blocks if necessary. I can live with the back being slightly imperfectly glued (if absolutely necessary) since it serves mainly acoustic purposes, with the added benefit of adding stiffness to the instrument.

This is great news since it means that while I will have to make some adjustments to the instrument to make the back glue on properly it will not affect the construction of the front of the mandolin.

Sometimes it's better to be lucky than good.

Out of the clamps

Just before leaving for my dad's place for Thanksgiving dinner I took the tail block glue-up out of the clamps. Like the neck block glue-up this one went swimmingly. Please ignore the wrist strap hanging down in the photo to the left.