I have been reading By Hand & Eye By George R. Walker & Jim Tolpin. Going through the construction of angles and geometric shapes at the end had me a little puzzled. So there is a set of drafting instruments in my office/computer room/library/man cave.
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The pair of dividers, under the beam compass, was taken to my bedroom since that is where much of my reading is done before falling asleep.
I hadn't given them much attention in the past since there are many others out in the shop that get used all the time. The little wheel between the legs got me curious. Turns out it might be a fine adjustment for the legs. It only changes the span by 1mm. That is likely enough for many purposes.
One thing I wish the book, By Hand & Eye, did would have been to better explain the constructions. The write up on the construction of a 45º angle doesn't explain the point above the vertex of the angle is a ghost construction of a 90º angle. It also doesn't explain how stepping off two radiuses on one of the arcs creating the ghost angle produces a 45º angle. Believing it works is one thing, but for me knowing why has it's values.
In the construction of polygons, for many polygons stepping off with a pair of dividers may be the best way. Though in high school my instructor showed us an easy way of constructing a pentagon using a compass and straight edge.
jtk
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