Top and back

Over the past two days I have glued the top and back onto the mandolin. This was much simpler than I expected (as, in fact, most of the project has been). First, though, I made some spool clamps. These are expensive - about $20 for a set of six from Stew-Mac - but simple. Basically they consist of a threaded rod with a wingnut for tightening and two short (about 3/4") lengths of dowel. To do it right you have to pad the dowel sections with cork. Since this is so straightforward, and since I happen to have a full woodshop with a chop saw and a drill press, I made my own and saved about $60. They aren't as pretty as Stew-Mac's, but they're perfectly functional, as I learned and you will learn below. Here is a shot of the spool clamps all laid out and ready for the top glueup.



I cut all of the dowel sections at once, and then cut little squares of cork and little squares of waxed paper. I drilled the dowel sections first, and then made stacks of cork and waxed paper so that when threaded onto the rod there would be a piece of waxed paper between every two pieces of cork (to keep the cork, and hence the jaws of the new clamps, from getting glued together) and drilled the stacks with the same drill press setup. I then threaded them all on one threaded rod. There was a nut and a washer at one end, and then I threaded a piece of dowel, a cork/waxed paper/cork stack, and a piece of dowel. This sequence was repeated until all pieces were on the rod, when I then put a washer at the top and threaded on another nut. I tightened the nut, and presto! the whole thing was clamped and glued.


Lesson learned - if you do this, wax the threaded rod before the glueup. The dowel sections stuck to the rod in some places and required some effort, including a heat gun in two or three cases, to get them off the rod. Oh, and the rod was toocaked with hardened glue to use for making the clamps themselves as well.

These pairs of dowel were then threaded onto 6" pieces of threaded rod with a hex nut at one end (the fixed end) and a wingnut at the other end (the moveable end) with big fender washers under both nuts.

These clamps are invaluable for gluing on the top and back. With the cork lining you don't even need cauls.

I then glued on the top. Here are some photos:











And here are the results:













I did the back today. Photos:

Fitting the top

So I finally got to work a bit on the mandolin this weekend again.

Today I glued the back brace onto the back, cut notches in the kerfing for the top braces to fit into, and trimmed the top braces so that they fit into the notches behind the sides.
First I glued the back brace on. Since I already wrote ad nauseum regarding gluing braces when I wrote about the top, I will refrain from kills virtual trees here repeating that information. I'll just show a picture of the back and back brace glued up. Next step for these pieces is carving the brace.

The next step is to fit the top to the sides. To do this you start out by cutting notches in the kerfing so that the top braces, which in some cases extend almost all the way to the sides, can fit. We start out by lightly clamping the top to the sides, making sure that the centerlines align, and also making sure that we are clamping to the top (as noted in a previous entry the hole for mounting the neck is offset towards the back so we have to make sure we clamp the top onto the correct side...). Then we make marks on the sides where the braces protrude, and then transfer those marks to the kerfing, which we are then going to notch out. Per the instructions I used my handy Xacto knife to cut the notches. Here are some photos of the process.

Finally you have to trim the braces so that they are short enough to fit. I used my trusty Marples pull saw and a chisel. Here are photos of that:

And here is the top, "snapped" into place with the braces in their notches.

Recent work

Well, I've had a bit of a hiatus while I took care of some personal business in the past few weeks, mostly related to a small but significant bit of elective surgery I had over the past weekend. For the record it was not plastic surgery of any kind...

At any rate, over the several weeks since my last post I have accomplished a bit but not had time to post about it. Actually, I also failed to take photos of most of these steps, but fortunately they aren't really visually gripping steps to miss.

What I did over the past few weeks was exactly what I said my next steps would be in the last post. I glued the short braces onto the top and sanded the kerfing to match the radius of curvature of the top. Fortunately the kit builder again thoughtfully configured the sanding stick setup so that the sanding stick, with the additional pad attached, resulted in a radius of the correct curvature. Basically you attach a strip of self-adhesive 80-grit sandpaper to the end of the sanding stick (7" in from the end, actually) and then, keeping the additional pad on the side of the instrument directly across from the area being sanded, you just sand the edges until you have properly contoured and leveled the kerfing. To aid in doing that you scribble with a pencil all over the kerfing. When the pencil lines vanish you have done your job. The key here is to keep moving around the circumference of the edge to ensure that you remove material somewhat evenly.

Here's a photo of the sanding stick setup. See the strip of sandpaper attached to the stick, and the additional pad? This photo was taken after some sanding of the top edge of the sides.



I also glued on the short braces for the top. I can't do any additional gluing of top braces, or really of the bottom brace either, until I get a set of more or less lutherie-dedicated cam clamps, so I'm somewhat stymied at this point. I failed to take a picture of the top with both braces glued-up, but rest assured that the process was identical for both braces and that the top pretty much looks just like this, but with two braces attached. Here is a photo of the brace being glued from the "inside".


And here is a photo of that same gluing operation from the outside, showing a piece cutoff from the top being used as a caul to protect the top. Note that cauls were not used on the braces since they have to be carved and will lose much of the material in the area that the clamp would have been bearing on anyway.


And, finally, here is a photo of the top with one of the two short braces attached.


I also spent some time tuning a bench plane which will be crucial to the shaping of the braces and neck and to the trimming of the top and back to the sides. I never really understood that almost all planes, and other woodworking cutting tools like chisels, require substantial preparation in the shop before they can be used, even if they are purchased brand new. While some of the very high-end planes might come with flat soles and very sharp irons, most do not. On a bench plane you can also spend a considerable amount of time ensuring that the bottom is a true 90 degrees from the side of the plane. Fortunately in my case the sole was very flat when the plane arrived, and the sides were close enough to 90 degrees from the sole to be acceptable for my purposes. I am somewhat surprised by this since because this is just a bench plane and not a high-end plane like a smoothing or jointing plane I bought a Stanley and not a really good plane. But a few minutes of (frankly) significant exertion really got this plane into usable shape. Mostly it was just flattening the sole by polishing it on 80-grit sandpaper adhered to a piece of polished granite I got through my previous employer that is truly flat and very, very stable. I then polished it with ever increasing grits until the sole was flat and mirrorlike. I have yet to sharpen the iron in exactly the same way before being completely pleased with the tool, but it still makes impressive shavings despite the relatively cheap nature of the tool. But this is a bench plane, after all - how accurate are we really expecting it to be?

At some point I will post some details about my sharpening system. Basically it is the Scary Sharp system (link, perhaps not to the originator of the system using that name, to the right), using a Veritas honing guide and several pieces of polished granite with various grits of sandpaper stuck to them. My good friend Joe Barker, who is building a sailboat in a room about 5% larger than the boat and blogs at http://barkerboat.blogspot.com/, uses the same system (I gave him several pieces of the granite, too) and he has more details at his site. Ignore all the Old Style comments over there. He has great taste in beer (and women) - he just wants to feel like a boat builder and you just can't get Narragansett beer in Cincinnati.

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.