February 14, 2019 – Precision Woodworking with Jigs – by Sylvan Wells

February 14, 2019 – Precision Woodworking with Jigs – by Sylvan Wells

Our February meeting included a presentation by Sylvan Wells on Precision Woodworking.   Sylvan is a luthier who specialized in guitar building.  Although this is a highly specialized aspect of woodworking, many of the precision methods he uses are transferable to general woodworking.  Sylvan showed us several jigs that he built and uses in his profession.

A principal that guides his jig making is that you must know the “cut line”.   Most of his jigs reveal where the cut will be made directly on the jig.  This way the piece can be positioned on the jig and aligned with the cut line for accuracy.  

He demonstrated this concept with a tablesaw jig used to cut curves in thin strips of wood for bracing.  The jig rides in the T-Slot of the tablesaw.  It was built oversized at first, then placed in the T-Slot and trimmed to size.   This revealed the exact placement of the saw blade on the jig.   In use, the strip of wood is placed on the cutline of the jig, ends clamped, and the centered bowed out into the path of the blade.  After the cut, the braced is removed, and springs into its original position resulting in a concave curve.   Stops on the jig ensure that this process is repeatable for all the braces.

The next jig was an adaptation of the familiar cross cut sled.  His was a dedicated miniature version for cutting a 82-degree angle for “X” braces on the tablesaw.   Again, the “cut line” clearly visible on the jig.

His next jig is placed directly on the guitar body with the edge of the jig, the “cut line”, perfectly aligned in reference to the guitar body.  This jig guides a router for inlay work.  

Jigs are not only for precision, but for speed and repeatability.  Six holes need to be drilled in a guitar headstock for the tuning pins.    The position is the same for every guitar.   Sylvan made a jig from PaperStone (a popular material for countertops) which holds the headstock on top in the correct position.   On the underside of the jig are six registration holes.  A drill press is setup with a waste board clamped to it.   Using an “F” drill bit, a hole is drilled into the waste board, then a registration pin of the same diameter is inserted into this hole.  Each registration hole on the underside of the jig, is placed over the registration pin, one at a time, and the hole is drilled for each tuning pin.

Other tips Sylvan gave us include:

  • Using Draftsman’s proportional dividers for finding the center of any number of divisions.  His was an eBay find of a German made steel unit.  
  • Also, he avoids using pencils for marking because they introduce errors.  
  • Some of his jigs use a screw for fine adjustments.  He standardized on ¼”-20 threads because (at 20 threads per inch) one full revolution is equal to .050” and one-half revolution is .025”.
  • When needing a rectangular hole in a jig, rather than trying to cut it out, Sylvan will laminate 3 pieces of wood together, edge to edge, leaving the proper size hole in the middle.  The middle board is cut to the width of the rectangle, cut in half, and spaced to the length of the rectangle.   This is far easier and more accurate.
  • Another eBay find was a set of metalworking transfer punches used to find the center of any hole.
  • Shrink tubing is used on drill bits of any size to act as depth stops
  • Using 3M brand #233 green masking tape for some clamping jobs.
  • Using hide glue for visible joints and PVA for all other joints.

Sylvan wrapped up his presentation showing us a prototype of a guitar.   This guitar is unique in that it has a slanted bridge and frets making each string is a different length.   Hence, tuning is not wholly dependent on the tension of the strings.   He got this idea from looking at pianos.  Picture the shape of a grand piano.  The case is physically larger in the lower octaves to accommodate the longer strings needed for base notes.

Joe Kunzman

Joe is a retired CPA and Sr. IT Data Storage Architect. He resides in Lake Helen, FL with his wife Marie. His woodworking interests include cabinetry and building 18th century reproduction furniture. He is also the Florida Chapter President of Society of American Period Furniture Makers. When not making sawdust, he also spends his time building embedded systems with microprocessors, such as Arduino.

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