A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Noell Wilson
Date: 2021 Jun 18, 08:02 -0700
Even failures might add something to the discussion.
I tried my version of a Bygrave many years ago. It was comparatively simple but just didn’t work well enough.
I used PVC tubes and scraped and sanded the outside of the smaller, 26 mm final OD, tube until the next size up, 34 mm OD, would slide on it. I finally managed to print Sin/Cos scales and corresponding value scales- D scale on a slide rule- that wrapped almost exactly.
Both scales on a 34 mm OD x Pi x 20 wraps gave 2136.3 mm total length of scale. I just checked and Sin 6/Cos 84 gives 0.1044. Actual is 0.1045.
But, the plastic tubes were sticky feeling against each other and the floppy clear plastic cursor was too aggravating to use. Another, clear, plastic tube with a cursor line would be much better.
As you may see from the multiple “arrowhead” marks on the cursor, I had problems running off the scales when trying to make the CosL-CosD-CosT calculation.
I think PVC tubes could be a reasonable choice. A felt interface, perhaps with some type of lock, and a clear outer tube with a cursor line might make a reasonable package.