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April 15, 2018

Making a Bowlback Mandolin Pt. 2

Mandolin Pt. 1 >>

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In Part 2 the form is finally getting finished and it's almost time to lay the first stave - known as the "keel stave". Turning it around and around and viewing it from every angle as I shape it, I find that it's important to trust your eye.

Now that I'm getting near the end I am using a Japanese Shinto rasp and here's a tool that should be in every wood worker's tool box. I've had this one for more than 30 years and it's still going strong and it does a great job.

After sanding I cut the front off of the form and this is where the neck block will go. This has to be a very accurate cut because the neck block is a small piece of wood that is responsible for holding the neck and the body of the mandolin together.

If you've been following OpenWoodShop you may have seen the Strip Sander I built a while back and it's finally in use doing what it was intended to do, finishing off the staves for the mandolin back. I'm milling these down to about 2mm.

And along the way there are a couple of more jigs to make. I make a kind of a poor man's jointer. It will allow me to sand edges that are perpendicular to the face of the board which will be essential when I am gluing the top boards together but it's also good for other parts as well.

Another jig is for sawing those tiny little spacers. They are about 2mm square and if I first get it started with a saw, I can finishish it off with a razor without the wood grain pulling my blade off track.

After the neck block is squared up it's time to put a dovetail on one side. I'll take out the bulk in the middle with the table saw and finish it off on the router table. The block is about twice as big as it needs to be but that gives me a good sized piece to work with while running it through the saw and router.

I also cut a small piece of maple that will eventually be glued right into the neck and then slip into the neck block I'm building. The fit couldn't be better.

The neck block is fit very accurately onto the form and held in place with 2 screws. Trace around the body, and then the block comes back off for shaping. I'm still working out what works best for shaping. I took a lot off with the band saw and then got closer to my lines with the belt sander. And now I'm back at it with the rasp, doing my best to cut the facets so that they line up with the staves that will be coming.

I'm using Robert Lundberg's method of making and fitting the staves. Here you see a previous attempt and it didn't really work out that well - the shape was difficult to control - so we'll try again.

And finally. The time has come to bend those staves. Here's where all of the work that I've been doing will tell the tale of whether I've done my prep correctly or not. The shape of the first stave is on the plans that I have and I heat bend it until it fits the form. Push pins, straps, and a clamp will keep it in place until it cools down.

The spacers also have to be bent.

After the stave comes off of the form the edges have to be bevelled and interestingly enough this just means laying it down and sanding until the edge is completely bevelled. Which on a piece 2mm thick takes no time at all.

The stave goes back up onto the form and is glued to the neck block. And finally the spacers get glued onto either side of the stave, held in place by more push pins.

And so that's it for the day. The rest of the ribs will require a lot more work to fit. They get bent first and then shaped to the rib before it. That's what I'll be doing on the next video and it should be a lot of fun.

If everything goes right.

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