When Straightedges Go Bad!

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.

Planing the fretboard with a high angle plane

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.

Remarkably scary fretboard sanding block

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.

Accurate perception is relative

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.

Using a level as a straightedge

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.

I think I got lucky!

7 thoughts on “When Straightedges Go Bad!

  1. Hmmmm, one of many things to consider when looking for an instrument. Does every luthier take these things into consideration or are this exact? Me thinks not. 🙂 Then again, what do I know?

  2. Doug

    Yup. I would think the maker should replace it. A non-straight straight-edge is not worth very much!


  3. Hi Gary,

    Thanks for the tip. Makes sense that graduations could cause stress or weakness. This straightedge didn’t have them. It was made by a reputable maker and is only a few years old so I may give them a call and see if they have any ideas.

    The Moxon disc arrived quickly. I’ve been too busy to check it out but I am looking forward to it!

  4. Doug… if memory serves, the best straightedge for gauging is one lacking any measurement markings. I think it’s the stampings that contribute to the loss of the edge over time, what with expansion and contraction. That’s a memory dug up from, oh, around 30 years past!


  5. Thanks Kari. It is a mystery how it warped but I’m glad I figured it out when I did!

    Some good has come from the experience though; I have a #4 and #5 1/4 plane that I know are very flat and true and I tried my hand at planing the fretboards and skipping the sanding. It worked very well, at least on clear, quartered walnut. The sole of the planes provided the “straightedge” and anytime I can avoid sanding I am happy!

  6. Glad you solved the mystery before your dulcimer was ruined. That would never have occurred to me to check the flatness of the steel straightedge. Now I know!

Comments are closed.