Sunday, April 5, 2009

Cutting F-Holes, Tone Bars, and Gluing on Soundboard

Sunday, April 5, 2009.

While it was a short week and I wasn’t able to spend as much time on my project as I would have liked, I still accomplished some of the more impressive steps to date and am very pleased with where I am.

Having been out of town on Saturday, Sunday and Monday of last week, I got back to work on Tuesday evening by first removing all my clamps from where I left them last Friday and then cutting out the F-holes in the soundboard.

The photos above show the results of my gluing on Friday.

As I started to cut the F-holes I was a little nervous about this step since the soundboard is so thin (as little as .01”) and I was planning to use a powered scroll saw to do the work. My fear, naturally, was that the scroll saw would cause cracks or some kind of chipping. My other option was to try to cut these manually using a hand-held scroll saw with one hand while trying to steady the soundboard with the other. While the manual method would likely help prevent chipping and cracking, I opted for better material handling control and went with the powered method. I figured the gauze I glued in earlier was my insurance against damage. As Mr. Siminoff suggested, I made sure to cut slowly.

I started by drilling four holes, one in the center of each scroll “balls” (best description I can think of on short notice) using a small 1/6” bit as a pilot followed with a larger 1/4” bit which is big enough to allow the scroll saw blade to be inserted. Then with these four holes drilled, I moved over to the scroll saw and began cutting.

In this picture, you can see where I have made my first cut from one hole to the other and am getting ready to cut around the ball.

As I did this next step, I learned something - cut out the ball first and then cut the long stretches. Here is why; as I made the cut around the ball, the “stretch” cut (my term) completed earlier, I found that the wood was vibrating badly and realized that the inside point where the stretch cut meets the ball was having to handle all that vibration with no support. Had I cut the ball first and then the stretch, starting the stretch cut at the point, the stress from the vibration would have been shared by a lot more wood rather than just the point. I hope that makes sense.

In any case, the points on this first F-hole made it through my abuse and I went successfully on with the second one much happier with my new-found insight. Here are some photos of the finished results after some sanding.

That pretty much did it for Tuesday night.

Wednesday I started with the tone bars. Back when I started this project, I made it a point to save pretty much all my scrap wood so, when it came time to make these, I was able to cut them out of the scrap pieces I saved from the blanks used to make the soundboard itself. Once I had cut out my tone bar blanks as per the dimensions in the book, I needed a way to transfer the shape of the inside curve of the soundboard to the bars so I could cut them to fit. To do this I went about as simple as it gets. I took a small piece of scrap side wood and taped on some lead from my mechanical pencil. Holding this in my right hand while holding the tone bar blanks in position with my left, I gently traced the curvature onto the blanks.

The razor blade (that’s saw dust on it) is there for reference.

Once I had the blanks marked I cut them roughly to shape.

Then I went through the time-consuming process of sanding and shaving them to actually match.

Then it was time to glue them in place. For this, I used three clamps one each tone bar with leather cauls on the back side of each clamp and a board on the from to help distribute the pleasure more evenly. As with most gluing procedures, I finished of the night with this step and left them to dry for 24 hours.

These photos only show the first of the two bars being glued. I glued the second one on right after taking the pictures.

Thursday I removed the clamps and did an initial crowing and cleaned the edges of the joints between the bars and the soundboard.

That is a pencil mark on the front edge I used as a reference while fitting the tone bar, not a crack. It actually fooled me once while I was working on it, too.

Come Friday, it was time to glue the soundboard to the sides. This process was one I had been looking forward to with both excitement and a little bit of trepidation. I figure this is where it starts coming together or you find out you have to take some big backward steps. While I frequently compared my soundboard to the side assembly at each stage of the process, I couldn’t help but worry. Fortunately, nothing seemed too out of whack to prevent me from gluing up, so I went for it.

For this, I used my 40 cello clamps, the side mold for reference, and hide glue. After preparing the clamps and getting the hide glue to temperature, I spread the glue and worked as fast as I could to clamp the soundboard in place. Here’s how it looked with all the clamps in place.

I was concerned with the time that it took to get all the clamps on since I have read that the hide glue dries quickly, but I figured that even though it took longer to complete than I wanted, I would wait and see how it looked once dried and, if necessary, take it apart and try again if it didn’t hold. With that, I was done for Friday.

Saturday was completely a wash as far as mandolin building goes since my wife and I decided to go to an auction that ended up lasting all day. We got some good stuff, but boy, what a day. Once we got home and got unloaded, it was about 9:00 pm, so about all I had time for was to unclamp and inspect my glue joints. It appears that contrary to my worries, my clamping speed was sufficient and the joints are tight. Here is how it came out.

I’m going to have even less time available next week so I am not sure if I will get enough done to really be worth posting, but I probably will anyway. Until then.

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