3 Thacher Replicas

My first replica was of a Thacher, and after Mike Konshak put its picture on the International Slide Rule Museum site enough people contacted me that I was encouraged to make a couple more using different designs.

Pictures of these efforts are on this page.

Building Your Own

Click here to see how I build a Thacher v3. I invite others to build their own replicas and let me know how they work out. Or just take a look to see what you get for $750.

Version 1

In my first effort, I built the cylindrical cage of triangular bars (called the "envelope") by cutting 4 wood end-rings, gluing pairs together, and then cutting triangular notches into one side of each glued pair. Those notches could then receive the ends of triangular bars which were prevented from falling inward by a strip of thin brass sheet glued to the inside of the wood rings. The assembly rotated in recesses routed out of end supports. The supports were mounted on a base board and a 4" piece of acrylic pipe with wooden endcaps served as the central drum (or "slide").

Version 2

In my second effort, the ends of the envelope were fashioned from brass and copper sheet soldered into a circle of triangular prisms to hold the ends of the bars. Instead of having the ends of the envelope rotate within recesses in the end

supports, I made the supports much thinner and attached circular ridges on which the end could ride.

Wayne Harrison and I worked on replicating the instructions affixed to the base of real Thachers for this replica. Lots and lots of proofing there!

Version 3

The third go-round, I tried to emulate the original Thacher mechanics as much as possible, but using wood for all the brass parts. I was very happy with these results.

I've actually built this version two different ways, call them v3.0 and 3.1. In 3.0 the envelope end rings are milled, and in 3.1 they're assembled. The pictures below show the milled end rings (the gold-painted rings at the ends of the envelope). They are rings with a square S cross section. Little triangles of wood are glued around the inside to form V's into which the ends of the triangular bars are glued. See here for how the end rings are made in 3.1. The 3.1 rings more closely match the size of a real Thacher's, so I prefer them.

The first 6 pictures below show the replica envelope vs. the envelope of a real Thacher stripped of its (ruined) scales. Real Thacher envelopes were made of steel bars welded to brass end rings. The bars, which were really open "Vs", were stuffed with fabric bats so that the metal didn't scrape the surface of the slide. The replica has solid oak bars instead which are glued to the end rings. To get a good look, I painted the rings gold and glued strips of brass to their circumferences.