I have long relied on a steel straightedge to assure that anything that needs to be straight or flat is indeed straight or flat.
I have treated this steel straightedge very well, keeping it from direct sunlight to avoid warping and storing it where it would not be bumped or abused.
Today I was having a very difficult time leveling a fretboard. This is usually a straightforward task; I check the fingerboard with the straightedge and mark any high spots and plane them down.
I follow up the planing with a remarkably scary sanding block. The block is trued by planing and it’s straightness is also checked using the straightedge.
Once the fretboard is dead flat I plane and sand a bit of relief into the fingerboard. I check the depth and curve of the relief by placing feeler gauges between the straightedge and the fretboard.
After several failed attempts to get the fretboard dead flat I was perplexed; perhaps I was having a bad day, perhaps my sense of perception was off.
And then I thought that possibly “old reliable,” my trusty straightedge may have made the transition from accurate tool to annoying metal object.
And it had!
Both edges are no longer truly straight. They both have a bit of a wave to them. I don’t know what caused this to happen.
The mystery was solved but what to do now?
I have a 3 foot level that I have assumed was fairly true. I checked it and found that one side was dead-on straight! It’s a bit flimsy so I have to be careful not to flex it when using it as a reference.
The straightedge was expensive.
The level wasn’t.
When I bought the level I looked for the straightest one by placing them all against each other till I found one that seemed the flattest and most true by eye.
For some time I have relied on an outside mold to maintain the shape of a dulcimer during assembly.
This type of mold helps keep the body symmetrical. Recently I have desired more flexibility during construction. Sometimes I’ll be working with wood that asks for a slightly different body shape for both acoustic and aesthetic reasons. I am also currently working on a dulcimer that is an experiment in subtly departing from the usual goal of symmetry.
Traditional classical guitar makers often construct instruments on a work-board called a solera. The solera also serves as a jig providing references for the geometry of the instrument and allows for some flexibility when determining the shape of the body.
I’ve recently started using a solera. The geometry of a dulcimer is much simpler than that of a guitar. My current solera is simply a heavy piece of plywood glued and screwed to a brace. The brace keeps the solera flat and allows it to be mounted in a vise.
The flatness of the solera is my reference for keeping everything square and parallel during assembly of an instrument. The solera also provides a good surface for gluing and shaping braces. The elevation above the bench and the contoured outline of the solera help make various clamping procedures much easier to perform. The extra few inches of height above the bench makes working much easier on my back too!
I can control the shape of the dulcimer by using spacers both within and outside the perimeter of the instrument. My standard pattern is easy to set up using a few spacer blocks and one clamp at the waist. I have the pattern drawn on the solera in pencil to help me line everything up.
When using an outside mold I glued the soundboard to the top of the sides face up. With the solera I glue the soundboard to the sides by laying the soundboard face down and clamping the sides down from from above. Cauls placed around the edges of the top and back make simple work of adding arching if desired.
I enjoy the simplicity and the freedom of working without a solid form. I am thinking of making some simple add-on attachments to assist with other aspects of construction.