I got a comment earlier asking about the process behind coming up with the Galbert Caliper. I am so close to getting the new Drawsharp in my hands from Jameel at Benchcrafted that I can hardly contain myself. So I thought I'd show a little about how these things come to be.
The calipers were born out of pure frustration with all the other methods that I tried for measuring my turnings. I won't go into it, but suffice it to say, I hated the first part of every turning. Then, one day, I noticed how the large part of a chair leg was harder to clamp in the v blocks that I use to drill mortises because it didn't seat as far as the small parts. When I realized that measuring the distance that each one went into the v block could be translated into the diameter, I dropped what I was doing and made my first crude caliper. You can see it at the top of the image below. I made it by grinding an old plane blade.
Above is a partial series of the caliper prototypes. The early ones worked great, but the range of the tool was limited and the "jaws" were so long that they would hit the tool rest. So I started thinking of other ways to translate the linear motion of the "stylus" to a rotary motion that could use different angles and ratios. I called upon a former student who was a rocket scientist to work out the math for me and I came to what I thought was the best angle for the largest range of measuring.
I am a big believer in ugly prototypes. The point is to prove the concept, not to be pretty.
I can't wait to present the new Drawsharp and the Adze that Tim Manney and I have been developing. The process is such a pleasure, that having an actual tool in the end feels like icing on the cake.