DIY Network

Handmade Guitar, Part 14: French-Polish, Neck and Bridge From "Handmade Music" episode DHMM-104

Dudenbostel #050, the fiftieth in a series of modern handcrafted guitars built in the tradition of the classic Martin guitars from the 1930s and early '40s.

In this segment of DIY's Handmade Music, Lynn Dudenbostel finalizes the guitar's wood finish with a French polish, then joins the neck to the body and installs the bridge.

Materials:

Cotton pads
Shellac
Walnut oil
Grain alcohol
Safety glasses or goggles

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Figure A

French Polish

The final phase of finishing the guitar is the creation of a smooth surface through a technique known as French polish. French polishing is just a method of applying a thin coat of shellac, using alcohol as a thinning medium, to create a final luster. The technique delivers a gloss to the instrument, and it's the only way to create the desired richness when using varnish. But there is a dilemma. Any amount of finish on a guitar hampers the sound in some way, but some form of finish is necessary. Applying shellac in the spray booth now would add too much finish. French polishing solves the problem.

The polish is achieved using a mixture of pure-grain alcohol, shellac, and walnut-oil (figure A), and the ratio of ingredients is learned through experience. Lynn's main objective is to find a balance between dry and saturated. Both extremes will hamper the effectiveness of French polishing.

• The mixture is applied meticulously by hand to the guitar's surfaces using a cotton pad (figures B and C). "You start out with lighter pressure on the pad," Lynn describes, "and as it dries out you apply more and more pressure. As you progress through the process of French polishing, you add less shellac and more alcohol. That helps smooth everything out and you get to the point where you're not building up any more, but just 'finishing the finish.'"

  Figure B

  Figure C

  
  
  
• With each pass of the cotton pad, Lynn leaves a micro-thin film of shellac (figures D and E). As the alcohol dries, the strokes leave what Lynn calls a "comet trail" resulting from the alcohol quickly evaporating as the mixture is applied. This cloudy appearance upon application is indicative that the finish is being applied properly. "Outside of selecting the wood, and knowing what to listen and feel for," says Dudenbostel, "if there's any other part of this process that seems magical, it's French polishing. When everything's going just right, it's a wonderful process."

  Figure D

  Figure E

  
  
  

With both the neck and body finished and buffed out, the two can now be joined together.

• Glue is applied to the faces of the dovetail and the bottom of the fingerboard extension, and to the surface on the body where the extension will join it (figure F).

• The neck is then placed in the body (figure G), and the two main elements of the guitar are finally joined.

  Figure F

  Figure G

  
  
  
• With the neck on the body, the guitar is ready for setup. Setting up a guitar includes adding frets, strings, and tuning pegs, but first the bridge must be glued to the top.

• Masking tape, which was added earlier, is now removed from the guitar top to reveal unfinished spruce wood at the bridge location. Hot hide-glue is applied to the raw spruce wood (figure H) and to the bottom of the bridge, and the bridge is quickly set in position. The glue is allowed to dry overnight.

• Once the glue has dried thoroughly, Lynn drills the holes for the six bridge pins through the bridge and spruce top (figure I). Once the guitar has been strung, bridge pins will hold the strings to the bridge once the guitar has been strung.

  Figure H

  Figure I

  
  
  

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

John Arnold, Luthier
Newport, TN

Ted Davis, Luthier
Loudon, TN