DIY Network

Handmade Guitar, Part 7: Kerfed Lining and Attaching the Back From "Handmade Music" episode DHMM-102

John Arnold holds an authentic and original Martin D-28 guitar.

In this segment of DIY's Handmade Music, luthier Lynn Dudenbostel continues work on the custom-built guitar, gluing the back and side pieces together.

Materials:

Rosewood stock
Mahogany kerfed-lining
Bending form
Saw
Chisel
Mallet
Clamps
Clothespins
Wood glue
Superglue
Straight-edge
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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Kerfed Lining and Gluing on the Back

In earlier segments, the guitar's rosewood back was built using book-matched pieces of Indian rosewood, and the back's internal bracing (made of red spruce) was added (figure A). Now work can begin in bringing the body of the guitar together by joining the rosewood back to the sides.

• To achieve this next step in the creation of the guitar, Lynn will uses kerfed lining (figure B). Luthiers use kerfed lining to create a wider surface area for gluing. The contact points for the kerfed lining is where the guitar's back top and back meet the sides. "This gives a little bit more glue joint," says Dudenbostel, "Once you put the purfling on the guitar and the binding, you've routed away most of the glue joint. So you need more surface area for the top and the back to be glued. That's the purpose of the kerfed lining." Kerfed lining can be ordered pre-cut from a luthier-supply company but, as with other steps in the process, Lynn prefers to make his own using mahogany.

  Figure A

  Figure B

  
  
• Lynn applies wood glue to the lining, positions it along the edge of each side and holds it in place using a large number of clothespins (figures C and D).

  Figure C

  Figure D

  
  Once in position, it's alright for the lining to rise slightly above the sides (figure E) since it will be sanded level later in the process. The important thing is to keep the lining from dipping below the top edge of the sides. The lining creates a sort of ledge for the top to rest against. Once glued, the bond between the top and sides is extremely strong and durable.

  After the top lining has dried for several hours, the clamps are removed, the body is flipped over, and kerfed lining is added to the opposing side (figure F).

  Figure E

  Figure F

  
  Once both sides are glued, and the glue has dried thoroughly, the clamps can be removed and the guitar is set on its side. Lynn measures the exact width of the side (figure G and H), and begins cutting reinforcement strips to that dimension.

  Figure G

  Figure H

  
  

  	Figure I
  	Figure J
  	Figure K
  	Figure L
  	Figure M

  The reinforcement strips will help stabilize the guitar and help prevent cracks from forming or spreading through the sides if the guitar is ever dropped or hit. The strips are 1/4-inch wide and are cut from rosewood stock (figure I). They are glued using superglue to five points spread along the guitar's inside surface.

  Once the reinforcement strips are in place, the next step is to level or contour the sides to accept the top and back. In the case of the top, Lynn uses coarse (100-grit or 80-grit) sandpaper attached to a wide board to create a flat surface -- while the sides, with kerfed lining in place, are still in the form (figure J). This creates a flat surface for gluing the top.

  "For the back," says Dudenbostel, "there's a compound curve going on -- a longitudinal and a latitudinal arch. The contour is changing. So the body is not as deep at the neck block as it is at the tail block." Lynn accommodates that curvature by planing a ramp into the head block (figure K) to allow the rosewood block to contact the sides, then slope upward and outward to create the compound curve. The curvature must also be accommodated when the kerfed lining is sanded so that it's no higher than the rosewood sides. For this, Lynn uses the sanding board for what he calls freehand sanding. "I'll take the board with sandpaper on it," he says, "and work those contours, changing the angle of the board depending on where I am on the guitar body."

  Once the sanding is done, the back is dry-fit against the sides (figure L) to check the contact points along the inside of the guitar.

  Lynn then marks the areas that will need to be cut away where brace wood and kerfed lining intersect. This ensures a firm fit without obstruction. He marks the contact points (figure M) then cuts away lining as needed using a hand-saw and a sharp chisel.
  Using a saw and chisel, he also cuts away portions of the back's bracing that extend too far into the guitars sides (figure N). Once he has the chisel positioned exactly, Lynn trims away just enough of the spruce wood to complete the fitting process.

  Tip: One of Lynn's tips for this step is to use the reflection of the brace in the chisel as a reference for achieving a perfectly straight cut with the chisel. When the reflection of the wood lines up perfectly so that the brace and the reflection looks like a continuous, straight piece (figure O) the blade will be at the perfect 90-degree angle to the wood for a perpendicular cut.

  Figure N

  Figure O

  
  After a final dry-fit to check the fit of the back with the sides, glue-up can begin. Wood glue is applied generously atop the kerfed lining (figure P) and positions the back (figure Q).

  Figure P

  Figure Q

  
  

  Figure R

  Finally, multiple clamps are used to hold the back secure against the sides within the form (figure R), forming a perfect joint as the glue dries.
  

RESOURCES :

Kentucky Thunder
For more information on the band that appeared in DIY's Handmade Music, Kentucky Thunder -- and to hear streaming audio and download samples of their music -- visit the website for Skaggs Family Records, www.skaggsfamilyrecords.com.

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