Friday, February 7, 2014

Fitting a Footjoint - Part II

We were upstairs on the production floor earlier this week when we ran into flute finisher Lindsey McChord fitting a footjoint.  We had a previous post on footjoint fitting (you can see the post by clicking here), but that post detailed how to fit a footjoint when the body tenon was too big.  So, what happens when the tenon is too small?  We had the chance to find out!

When we caught up with Lindsey, she had a Conservatory with a body tenon that was just slightly too small for the footjoint.  Additionally, Lindsey felt a bit of "rocking" when she placed the footjoint on the tenon, so she needed to expand the body tenon just slightly.  To do this, she placed the body on an arbor and began burnishing the tenon.  Burnishing is a process where the metal of the tenon is pressed against the metal arbor.  By doing this, the tenon metal expands from the pressure.  However, the pressure has to be very light, and you have to exert equal pressure all around.  Because the process is so delicate, Lindsey began by burnishing the tenon in about three spots.  She then tested the fit, and it was still a bit loose.  The initial three burnished spots on the tenon were visible as lines that had a bit of a "matte" finish.  Since she could see the initial marks, she then burnished the tenon in a few more spots between the areas that were burnished in the previous step.   Once again, she tested the fit.  It was good -- even a bit on the tight side.

Now that the fit was almost perfect, there was one more step needed to remove any marks from the burnishing process and get a perfect fit.  To do this, Lindsey used very fine-grade sandpaper on the tenon.  The rough side of the sandpaper is good for removing slight bits of material, so Lindsey sanded a bit with that side of the paper.  However, she also used the opposite, smooth side of the sandpaper to smooth out any marks.  Then, she took a tissue and wiped both the outside of the body tenon and the inside of the footjoint.  This helped remove any debris that might hinder a smooth fit.  After this, she tested the fit of the tenon once again, and it was perfect.  She then added the final step of a bit of polish to shine and smooth the tenon, and it was ready!

Recapping the process, it may seem simple enough, but it truly takes great skill and patience.  Every step in burnishing must be done in very small, light increments -- but the most important skill is the ability to feel the fit.  It's much more than a matter of  "too tight" or "too loose."  One must be able to assess the fit on many levels and feel the slightest imperfections.

Checking the fit of the footjoint.  It is a bit loose and "rocking."
Placing the body tenon on an arbor.
Burnishing the tenon with a burnishing tool.
Burnishing marks -- these serve as a guide, too, for additional burnishing.
Checking the fit again.  Just a tiny bot too tight now.
Sanding the tenon to remove marks and make it just a bit smaller after burnishing.
Using the opposite side of the sandpaper to smooth out the tenon.
Cleaning out any residue in the footjoint.  This was done on the tenon as well.
Checking the fit again -- perfect now.
After polishing, the tenon is shiny and smooth.  Done!

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