Summer Uke Build #6: Cutting Soundhole Making Radius Dishes

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Blog entry by onoitsmatt posted 10-21-2016 07:16 PM 953 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 5: Joining Back, Gluing Neck Block, Adding Rosette Part 6 of Summer Uke Build series Part 7: Tail detail/Kerfed Lining/Top Braces »

Today’s update is a bit incomplete. I cut out the soundhole and sanded down the olive wood rosette to be a little more level with the top. I bought a drum sander in the interim as I just don’t trust myself to flatten and thickness the top with any accuracy. I’ll send the top through the drum sander sometime soon to get the finished thickness/flatness for the rosette and top.

I put the back behind it for contrast in the photo.

I also have started trying to figure out how to do the radius dishes to radius the top and back. I’m planning to do the guitars with 20’ radius backs and 28’ radius tops, so am just going to use these radii for the uke build as well so I only have to make one set of radius dishes.

I could just buy some, but I hate to do it, would rather beat my head on the wall trying to figure out the best way to do it. There are some very clever solutions out there. One that I tried (and failed at) was to use 3/4” plywood and glue thin wooden “risers” that get progressively taller as they radiate from the center of the dish. Then attach a piece of melamine to the top allowing the risers to elevate the melamine from the center out, mimicking the radius needed. This proved to be pretty inaccurate, and difficult to get consistency all the way around. So am working on some other ideas at the moment.

The current plan is that I went into Microsoft Excel and opened a blank workbook. I inserted a shape (a circle) which defaults to a 1” by 1” circle. By choosing the properties of the circle, I was able to make the circle 480” tall (which would be 40 feet or a 20’ radius circle).

Through trial and error I found that to get a length of about 24” is about 34 cell widths from the defaulted width when you open a fresh workbook. So I added a column count from 18 back to 1 and up to 17 again.

The apex of the circle is shown in the screen capture below with the little rotate icon.

By selecting a section of the circle and choosing the “print selection” option in the print menu, I was able to print a 24” segment of the circle which (when printing landscape orientation on legal size paper) gets me a nice 24” segment of a 20’ radius circle.

Below are the left and right halves of the segment which when combined give me my 24” length to use as a template for my 20’ radius.

After printing, I aligned the left and right sides and taped them together.

Will probably paste these to some 3/4” baltic birch plywood and sand or plane them to the line. Then Either use them as a sled to rout out the radius dish or make a few of these to use to just shape the braces, etc. Haven’t figured that out yet.

-- Matt - Phoenix, AZ

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