DIY Network

Handmade Mandolin, Part 2: Hand-Shaping the Top and Back From "Handmade Music" episode DHMM-105

From this stage at Nashville's Ryman Auditorium, Bill Monroe introduced the world to modern bluegrass. He played the fabled Gibson F5 mandolin, the model on which this modern replica was based.

In this segment of DIY's Handmade Music, luthier Lynn Dudenbostel hand-shapes the mandolin top and back after they have been rough-cut using a computerized router known as a CNC machine.

Materials:

Red-spruce stock
CNC (computer-driven) router
Band saw
Finger planes
Hand scrapers
Sandpaper
Violin caliper
Hot-hide glue
Gauze reinforcement
Gluing fixture
Carpenter's pencil
Safety glasses or goggles

Safety Alert: Always wear safety goggles or safety glasses when
working with wood, power-tools, saws, drills, routers, etc.

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Hand-Shaping the Top

• After some additional trimming with a band saw, Lynn reverts to the old-school techniques using finger planes (figures A and B) and other specialty tools. Finger-planes are tiny, specialized planes that are also used by violin-makers.

  Figure A

  Figure B

  
  

  Figure C

• As he hand-shapes the top using the finger planes, he checks his progress periodically with a violin caliper (figure C) which measures the precise thickness of the plate.

• As he carves the plate to specific dimensions, he also tap-tests the wood occasionally to check its sound. "There will be variation [in the sound]," says Dudenbostel, "depending on the hardness of the wood, the stiffness. Each wood calls for individual characteristics in carving. That's why you can't just machine each one on a CNC to a given dimension. There still has to be that human input in carving each one.
  
• Once the hand-carving of the top reaches a certain point, it's taken back to the CNC router (figure D) to create the F-holes. These ornately shaped openings if the mandolin's top (figure E) are its sound holes.

  Figure D

  Figure E

  
  
• Lynn describes the essential function of the sound holes in the mandolin. "Without a hole in the top of the instrument," says Dudenbostel, "there's really no way for that body to project sound. You can think of the body of a mandolin or a guitar as an air-pump -- because any time you strum the strings the top vibrates, and there's air moving in and out of that sound hole. Without that, you'd have a very quiet instrument." For this process, computer precision of the CNC is a great asset because, while F-Holes enhance the look of the instrument (figures F and G), they are critical to the sound. There is little room for error.

  Figure F

  Figure G

  
  
• At this point, the top may look complete but it's not. The tone bars on the inside of the mandolin are created and installed next (figures H and I). Though they may look like braces, the mandolin doesn't require additional internal support; just acoustic enhancement. "In an arch-top style mandolin, the bridge can support the weight of the strings and the tension," says Dudenbostel, "without any additional support. The tone bars inside the instrument are just for transmitting the vibrations throughout the top."

  Figure H

  Figure I

  
  
• "Fitting the tone bars," he continues, "can be a fairly lengthy process because you have a very complex curve on the inside of the instrument. That has to be fitted by hand. I'll use finger planes, scrapers, sandpaper -- whatever's necessary. And it has to be an absolutely perfect fit." Once the tone bars have been trimmed to their final form and fitted, they are carefully glued in place using hot hide-glue (figures J and K).

  Figure J

  Figure K

  
  

  Figure L

• While the tone bars provide no support, the gauze strips over the F-holes (figure L) do provide extra strength. Lynn will cut away the gauze over the holes but the edges are now reinforced and that should prevent any splitting through the years.
  
• It's at this point that Lynn truly creates the sound of this mandolin. As he says, he is "giving the instrument its voice" as he carves the tone bars to specific dimensions (figures M and N). The dimensions and the carving techniques are gleaned from years of research. Lynn listens to the mandolins of yesteryear and, from their voices, he learns styles and techniques worthy of emulation. Every shaving removed from a tone bar affects the acoustics. This is deliberate and thoughtful work, and is the final step in preparation of the top.

  Figure M

  Figure N

  
  

  	Figure O
  	Figure P
  	Figure Q

• With the creation of the top complete, focus shifts to creating a back and later the sides for the mandolin. First, a single solid block of curly maple is used for the instrument's back (figure O). The stock must be thick enough to allow the deep carving required to create the curves of an F-5.

• After leveling the piece with a thickness sander, Lynn returns to the CNC machine and carves a rough approximation of the mandolin's back. Again, the machine is simply duplicating a shape chosen and programmed by Lynn. When the inner and outer profiles are carved, the shape is trimmed at the band saw (figure P).

• Once trimmed to shape, Lynn sands the outer portion of the back. The inner carving of the back must be done by hand and, like the carving of the top, the work is done with the finger planes normally used by violinmakers (figure Q).

• Lynn scrapes away the maple little by little until he hears what he wants to hear when he conducts his tap-test. Exactly what he's listening for is of those unwritten, elusive things that only a luthier with years of experience can know. As Lynn says, "When it's right, it's right."
  

RESOURCES :

Stewart MacDonald's Luthier Supply Shop
Website: www.stewmac.com

Luthier's Mercantile International, Inc.
Website: www.lmii.com

Pioneer Valley Luthier Supply Company
Website: www.pioneervalleyluthier.com

GUESTS :

Lynn Dudenbostel, Luthier
Dudenbostel Stringed Instruments
Knoxville, TN