A quick update on rosettes

Abalone and ebony rosette for Richard's ukulele

It's downright weird what I remember from science courses in high school. I always liked chemistry better than physics (too much math involved in physics.) One of the things that has stuck in my brain is the idea of a rate-determining step in a chemical reaction. As I understand it, the reaction can't go faster than the slowest bit of it. In terms of where I am in the ukulele building process the rosette is my rate-determining step. I need to get the rosette inlaid into the top before I can put the top on the building form and start bracing it. Once the braces are in then I can bend the sides and attach the sides to the top.

The top is pretty thin around 2mm. The reason I know that is that I measured it with my digital calliper which happened to be set to metric and I saw no need to change the units to imperial although that's what I normally use. With the same handy device I measured the rosette at its thinnest point .97mm. That means I have very little room for error or I'm going to have a hole in the top other than the sound hole which is supposed to be there. It's a good thing I like to putter along because this particular exercise has required quite a lot of puttering. I started Tuesday by drawing around the rosette with an X-acto knife and then deepening the line. When I first took the rosette off the top I could hardly see the line. Not deep enough so I carefully put the rosette back in place. Jake gave me the tip of putting 4 tiny dabs of glue on the rosette so it wouldn't move around while I was trying to scribe a line around it. That worked well and I was able to get the glue off when I picked up the rosette and I was also able to get the rosette back in exactly the same place with 4 more tiny dabs of glue for the second round of scribing. Then I removed the rosette and went at it again, this time using the cut lines to guide the knife going slowly and gently. Many light passes later I had a pretty good outline. Then I began to remove a bit of the waste up to the cut lines with a chisels.

Router plane, chisels, X-acto knife, digital calliper

I'm not sure how long that took me but I was pretty much cross-eyed by the time I was ready to come home. I carried on with that process yesterday and, once I had the shoulders delineated, I began to remove wood from the middle of the channel. I still had to be careful because it would have been easy enough to push a little too hard and tear the grain. That did happen in one spot but I think I know
how to fix it. I used both my chisels and my router plane for this job. To get the depth of the cut I wanted with the router plane I used feeler gauges, thin bits of metal graduated in thousands of an inch. I didn't need to worry about what the numbers said because I put combinations of the metal leaves beside the top until they were about half way up and then set the cutter accordingly.

When I'm doing work like this and it's going well I'm amazed by the effectiveness of some of the tools I use and I feel a real fondness for them. I experienced that as I worked with the router plane. How many people before me have used a tool like this to build instruments and furniture? How many people has it taken over the years to perfect the design? And, how many people in this age of CNC routers are turning back to hand tools simply for the delight of creating something with only hands and a sharp blade? I know it's the most rewarding thing I've ever done. The downside is that I find it pretty hard on my arthritic thumbs.

Not deep enough yet

Every once in a while I checked to see how thin I was making the top and whether or not the rosette fit into the cavity. I got the outline done pretty well and the rosette slipped in without too much trouble. Force it in an it's likely to break ... again. I think the number of times I've broken it, either on purpose to fix or redo something or accidentally stands at about 7. There was too much of it sticking up though. In woodwork-speak it was too 'proud.' The only choice was to do some more careful excavating, check the fit and repeat. The hardest part was trying to keep the walls of the cavity perpendicular and smooth. I resorted to using the chisel to pare down the walls because the chisel, unlike the knife has a flat back so it will go straight down the wall as long as I hold it straight. The knife has a V point so you get a sloped wall.

Lampshade anyone?

I thought it might be interesting to hold the top up to the light so see how thin it was getting. In one spot it was really thin and I put an X in pencil there I wouldn't take off any more material. Bit by bit I lowered the floor of the channel until I completely lost my nerve. There are no holes in the top but it sure is thin and I'm not prepared to try to get it any thinner. The rosette is still proud and I hope there is enough thickness to it that when I sand it down to make it level with the top I won't sand through it. The process can be a nerve-wracking and I didn't exactly pick an easy rosette to start on. Nonetheless, it's absolutely engaging work and, outside of the nervous-making quality of it, I'm thoroughly enjoying myself. Today I glue the rosette into the top. I can already think of a number of other possible rosette designs and I can't wait to try some of them out. I guess I'll just have to keep building instruments so I have an excuse to make rosettes. In the meantime I can get on with the next steps in building the two instruments I already have on the go. Stay tuned.