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:

Biggest day yet, part II

Blogger kept crashing on me near the end of the last post, so I elected to split them into two posts. If you haven't yet read about shaping the braces, read the next post before this one.

Here you can see the top and back, along with the cutoffs (which the plan suggests keeping for use as cauls later in the project). On the right are the three major components to date – the top, the sides and kerfing, and the back.

And here's an exciting photo – I stacked the parts together on the benchtop just for giggles and took a photo. At some point in the near future the instrument will be glued together like this and then the top and back will be trimmed to final shape. I just thought it would be cool to see it like this.

Since I still had several hours (at this point I had spent only about 1.5 of my 6 or so) I decided to cut out the soundhole as well. Now, the plans suggest cutting the soundhole patch using a hobby knife. I had been dreading this step because I was frankly worried that I would cut this poorly and damage the top by over cutting. It had to get done sometime, though – so here it goes.

The photo on the left shows the soundhole from the kit manufacturer with the soundhole patch glued over it. The photo on the right shows the results of the rough-in cut out (as suggested by the plans I made a first cut a bit shy of the edges of the soundhole, followed by a final cutout to actual shape). As you can see in the left photo below, I did some minor damage to the top wood surrounding the soundhole when cutting it out just as I had worried. However, the next step in the plan is to smooth and bevel the edges of the soundhole with sandpaper so I decided not to worry too much about minor damage. Fortunately the damage turned out to be very minor indeed – the photo on the right is the soundhole after smoothing and rounding with some 120 grit sandpaper (the MDF of my benchtop is also visible here, and it might make the soundhole hard to make out. Sorry.)

These last two photos are of the top after all the work of today was complete. The one on the left is of the inside of the top (the side that will not be visible after the instrument is complete). You can see the soundhole patch and the markings for all the braces in this photo. The one on the right is of the outside of the instrument.

Next time I will be sanding the kerfing to match the curvature of the top and back, and gluing in some of the braces. Not too long until the body is largely complete!

Biggest day yet

Wow! I got several hours to work in the shop today and the outcome was better than I could have imagined. My wife took the kids and went off the visit her parents, and she instructed me (this is why I know she's the right girl) to work on the mandolin. I got more accomplished today than any other day of work on it yet!

I started off by shaping the braces for the top and back. The kit includes a specially sized “sanding stick” made of ¼” plywood. They even included a little piece of the same plywood for use as a caul for clamping the stick to the benchtop. The kit designers thought this step out well, and planned for it well, too – the caul that was included for the outside of the sides at the neck block it just the right height at the edges to result in the proper radius of curvature when used to elevate the non-clamped part of the stick. The following pictures should give some idea of what the heck I'm talking about:

The photo on the left shows the stick clamped to the benchtop and propped up at the other end using the neck block caul. A clamp holds the neck block caul in place – I found that the two clamps at the bench kept the stick from rotating sufficiently. As directed by the instructions I also supported the stick at two other points along its length; one of the supports is the tail block caul and the other is a piece of scrap left over from the toolbox I built for my son for his birthday. The picture on the right shows the same setup from above just for clarity. You can see the self-adhesive sandpaper (80-grit as recommended) in the photos.

The instructions say to sand one of the braces and compare it to the drawings, adjusting the curve by moving the neck block caul in or out until the curvature is satisfactory. You then sand all of the braces using that same setup so that they are the same. I found that, by luck, my setup worked out very well the first time, so I went about sanding all of the braces to the curvature shown on the plans (which the instructions helpfully tell me is about an 8' radius).

The picture on the left is an action shot of me sanding one of the braces. I used a longitudinal motion to sand them – that is along the length of the stick and not side to side across it. This just seemed easier and the results were good, so I guess it's OK – at any rate it matched the grain direction so it made for clean sanding. The photo on the right shows the completed braces. Note that there are two #3 braces.

The next step is rough-cutting the back and top. I had not originally planned to do this today, but the shaping of the braces went so well and so quickly that I decided to have at it. The instructions say to cut the top and back with a bandsaw if you have one. Since I do I decided to give this a shot.

Up until today I had not had luck with my bandsaw, which I bought used (along with almost all of the rest of my stationary power tools) from a guy who was liquidating his shop. I examined the saw and realized that I had not been setting the damned thing up correctly. Not one of the cuts I had tried with it had been successful until today. Today I adjusted the tensioner more carefully and realized that I had not been properly adjusting the blade guide. After having done this the saw cut like a dream. Lesson learned – adjust your bandsaw carefully for each situation and it will cut much, much better.

I used the bandsaw to cut out the back and sides (the instructions tell you to leave about ¼” proud for later trimming to the actual shape of the instrument). Because I was not being very careful about accuracy since I was leaving the cut proud it went fast. I first had to mark the brace on the back and trace the outline (the left photo) and then cut it out on the bandsaw (the right photo).

Flush with my success I then cut out the top as well.

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.