Theodolite Graduations

I was given this theodolite some time back. With an eye on laying track around the house sometime in the future, and laying extra track at Richards House [1] in the near future, I want to use it for measuring the yard. While it can give me levels and distances as it is, it will be much more useful with a degree scale so I get full polar co-ordinates.

Such a graduation scale requires 2 things:

  1. it needs a vernier scale to get down to bits of a degree. This is easy enough
  2. it needs to be zero-able so that a set of readings can be started on some handy 'zero' direction.

My plan so far is to make a narrow ring that fits just above the sloped base part, with the vernier on the right side of the body portion. See pix below with explanations. In fact, just as I type this I have realized that I can make the ring of a size to fit about halfway down the slope, with the vernier on a 'balcony' hanging of the side of the body. This willmake both dividing and zeroing much easier.

PS: the manual describes the next model up which incorporates such a degree scale. It has a seperate optical viewer for that, and the scale itself appears to be contained within the body. That tells me that it is quite small and I don't really want to get into trying to divide really tiny divisions.

theodolite/th000_1043.jpg

Right hand side general view

Last edited February 20 2013 09:55:30.
theodolite/th000_1045.jpg

The mirror angled to show the bottom of the longitudinal bubble. In this orientation it supplies light for the bubble sighting eyepiece.

Last edited February 20 2013 09:55:30.
theodolite/th000_1046.jpg

The bubble level has a mirror that serves 2 purposes. When setting up it is used for sighting the round bubble that levels the body as can be seen in the relection here. When rotated up it supplies light for the longitudinal bubble level.

Last edited February 20 2013 09:55:31.
theodolite/th000_1049.jpg

A view from the 'rear'. Lower rear knob is level adjust. Top left eyepiece is the bubble level.

Last edited February 20 2013 09:55:32.
theodolite/th000_1054.jpg

This the slope on which I propose to mount the degree graduation ring. If I make it large enough to sit about halfway down the slope it will give an inch more diameter and hence a large scale, as well as being easier make adjustable. My first thought was to make a ring that would just fit the small cylindrical section as that is the obvious place.

Note that the extentions from the body to the right prevent anything stcking up beyond the top of the small cylindrical section.

Last edited February 20 2013 09:55:32.

[1] Richard owns a Sweatpea in 5" gauge, and has on oval of track in his yard where we run monthly public days.


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Last modified: February 20 2013 07:52:53.