Top Plate Machining

Before any voicing or tweaking can be done, the top plates must be machined.

Here’s the Cliff’s Notes version, in the form of a video…

The plates are bookmatched, jointed, and dimensioned by hand. As I am doing this, I try to get a sense of the individual piece of wood. I like to work with large billets so I can get as many tops out of one chunk of wood as possible. It just reduces the number of variables I have to deal with.

Once a clean, well joined top is ready, I modify the CAD/CAM program to be close to my target graduations, just a tad on the thick side. Depending on the wood, and whether it’s an oval-hole or tone-bar type instrument, the graduations may vary by as much as 70%.

Then the blank is placed on a vacuum fixture. Atmospheric pressure holds the part down with between 5-10 psi, so it’s like having a several hundred pounds of weight sitting on top of the piece of wood. It’s not going anywhere, as long as my little boys don’t run in and step on the hose…

Here’s the part after the first roughing cycle, which is under 5 minutes.
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Next, the inside is profiled to approximate its final shape. That takes another 6 minutes or so.
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Then the part gets flipped onto a different part of the same fixture.
flip fixture

Then the same roughing and profiling operations are performed on the outside of the top.
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Now the tops are ready for careful voicing and bracing, which is done by hand.

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