Monday, July 24, 2017

Day 153: Cutting the Bridges

As promised, I proceeded with sharpening all of my plane blades over the weekend. Frankly, I'm not sure I'm too enamoured with the ceramic wetstones. While I was able to get the blades plenty sharp, I didn't feel as if they are as sharp as I could get them. Yes, I was able to shave a little hair off the forearm, but it wasn't as if I was running a razor over it, so I shall continue the discovery process around getting the blades to where I want them to be.

Once I had finished sharpening all of the blades, I turned my attention to the bridges. Finally. As you may recall, I had chosen beech over cherry, both of which are traditional Ruckers bridge and nut materials. The bridges are the bent pieces of wood you see strings running over on the soundboard. The nuts are near the tuning pins by the keyboard.

The strings are stretched over both and, technically, the vibrating length of each string - the part that determines the pitch at which they play - runs between the nut and the bridge. On a guitar, this would be the part of the string that runs between the nut and the saddle. Unfortunately, a harpsichord is not fretted, so each key get its own eight foot and four foot (an octave higher than eight) string.

Cutting the bridges and nuts is an exacting process that's a lot like pulling one of your own teeth. First, they change width from end to end so that the eight foot changes from 3/4" to 1/2" over the span of the thing and the four foot changes from 1/2" to 1/4". The height also changes in the same way at the same measurements. And this includes a 35-degree cut on one of the faces, as well as a 30-degree bevel where the bridge pins are driven in to control the paths of the strings.

Following Mr. Miller's eBook Most Excellent pretty closely, I cut the 35-degree face into boards at the proper lengths for both bridges. As a side note, never rely on the blade angle degree indicator on your table saw - it's completely useless. The next fun part is to cut the line for the diminishing width (from 3/4" to 1/2"). I chose to do this on the Laguna 14" band saw with the 1" blade. I felt this would provide a straighter, more accurate cut and I was right on this one (journal entry recognition coming up).

Before cutting the 30-degree bevel, I went ahead and used the spokeshave to smooth down the 35-degree cut. No matter how well your band saw is set up and how thick the blade, it's going to wander a bit. Fortunately, the spokeshave made quick work of cleaning up the saw marks. I then cut the 30-degree bevel and smoothed it up accordingly.

As you can see, once I had the eight-footer cleaned up, I went ahead and cut and smoothed the four-footer. It was hot and humid in this part of the country over the weekend, so I took frequent breaks to cool down and hydrate. The shop side of the house gets the sun all day, which means I'm working in a nicely warmed oven when the temp gets into the 80s and above.

Today, I'll work on cutting the nuts. The process is similar to cutting the bridges only with shorter pieces. Now that I have a couple under my belt, it's not as intimidating as when I was making things up in my head. Sure, the cuts are difficult and one must be super-careful with the spokeshave and scraper, but if it were easy, everyone would be doing it, right?

On a tangentially related note, while I was working on sharpening the hand plane blades, I naturally had to disassemble them. Now, most planes are sufficiently simple in design so that it's easy to slap them back together. Not so for the Stanley No. 92 shoulder plane. I quickly realized I had no idea how it went back together, so I hit the Interwebs for the answer.

A shoulder plane is a nice tool for cleaning up rabbets and dados because the blade extends all the way to each side (not so for a typical hand plane). While the sides are not sharp, this still exposes more cutting real estate on the business end of the blade. While perusing the detailed information about the plane on the Stanley site, I discovered that the plane is intended to be partially disassembled to also become a chisel plane.

As you can see in the photo above, disassembly removes the "nose" of the plane, exposing the blade so that is can be used as a stable chisel to clean out corners when necessary. When I discovered this, I danced like no one was watching because, well, no one was. Mostly because it saved me $165 by obviating the need to purchase a chisel plane from my manufacturer of choice Lie-Nielsen. Sure, it's small, but, most of the time, that's just what the doctor ordered.

Until next time...

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