Fitting Tone Bars
© Frank Ford, 10/6/98; Photos by FF, 10/5/98
Tone bars not only help to reinforce the arched top of a guitar, but they also contribute greatly to the sound of the finished instrument.
Tom Ribbecke believes in fitting the tone bars precisely to the arch of the top:
And he's offered to show us his ingenious method of achieving a perfect fit.
First, he uses a compass with a pencil to scribe the bottom of the bar:
Then he rough-cuts the bar to the scribed line.
Next he mounts the bar in his special fixture which holds the ends down with little springs:
A few lengthwise strokes with some sandpaper, and the bar begins to fit the top very closely:
As the bar begins to fit right against the curve of the top, Tom adds another spring loaded plunger to the center of the bar to equalize the cutting action of the sandpaper. (I didn't photograph that part, because it obscures view of the sanding action.)
Here's the subtle, and really important stuff:
Tom showed me how you can tell if the bar is really fitting well. He strikes a tuning fork and runs it along the bar. As the fork travels, you can really hear a drop in volume of sound anywhere there is a gap under the bar.
This is a great technique, Tom!
Another hot tip:
After the bar fits just right, Tom carefully scrapes the gluing surface with a razor blade to improve glue adhesion and to straighten out any rounding over that the sanding may have created.
Visit Tom's shop
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