DIY transit from junk

[mklotz]

While cleaning out some ancient boxes in the rafters of Garaj Mahal today I stumbled upon a tool I had built a long time ago and had completely forgotten after carefully storing it away. Not everyone needs a tool like this but the story behind it is, IMO, interesting and it is a classic example of what one can make with just the junk lying around in a reasonably junk-fertile shop.

I used to have my astronomical telescope set up on the back patio. To aid in observation I had written a program that would indicate the rise times and positions of all the planets as well as a few other things of interest. Trouble was that rise times were all calculated on the basis of a mathematical horizon but there are mountains surrounding the LA basin, not to mention neighborhood trees and other obstructions.

If I could map the azimuth and elevation of these obstructions I could put that data in my programs and compute true rise/set times for my location, thus saving me a lot of waiting around. To map them I needed something akin to a surveyor's transit. (Using the astronomical scope itself would have been very cumbersome.) Transits are expensive and I couldn't find any local rental places so I set out to build one for myself.

I didn't need anything as accurate as a real transit and, with young children, money wasn't plentiful so I opted to build it from what I had. The first picture shows the completed transit...

Basically, it's a framework that holds a 0.22 rifle scope so that it can be rotated in both azimuth and elevation. These angles are read off two 360 degree protractors I purchased at the local stationery store (remember when stationery stores carried stuff like that, drafting instruments, bow pens, etc.?)

The base...

is a plywood circle set on three adjustable leveling legs. Mounted on this base is a giant ball bearing found in the "someday I'll need this" bin. The upper structure that carries the scope will ride on its inner race. A plate in the middle of this race is connected to a smaller wheel under the the base that, driven by hand, will cause the upper structure to rotate. Note the ingenious bearing clamps made from screws, washers and spent 0.22 cartridge cases for spacers.

This photo...

shows the upper structure attached to the plate. The protractor that reads azimuth can also be seen along with the index post at which the azimuth angle is read.

I was lucky to have an 18:1 planetary gear assembly lying around in the same bin from which came the bearing. It had been rejected from a spacecraft antenna pointing mechanism and I retrieved it from the dumpster. This gear assembly provides the elevation motion in a nice smooth way; with the reduction precise pointing of the scope is easy. Also obvious is the elevation protractor; its index mark is on the opposite side of the aluminum support that holds the planetary gear.

The scope had dovetail mounts so I had to machine a dovetail carrier for it. This carrier is screwed to the planetary gear plate that originally carried the spacecraft antenna.

A level was needed. I was too cheap to buy a good level so I built an adjustable mount for a line level (the type masons hang on a string to lay out a level course). The level mount is made from two discarded steam chests I made for one of my steam engines...

and later discarded because I changed the valve design and that required a slightly larger steam chest.

The level is soft-mounted and two screws (not visible in the photo) on the bottoms of the steam chests allow find adjustment of the level.

Certainly not surveyor accuracy but plenty good enough for my purposes. Only the protractors, and the scope were bought so I would guess the whole thing cost less than $20 in 1970's money. No prints; I made it up as I went along and that's the most enjoyable way to build!

[Frank S]

great build Marv Probably every bit as my first dumpy level that I used to build boat docks on a lake with a broken elevation protractor.

[Stevohdee]

Brilliant! Junk is just material waiting to be used, nice build

[Toolmaker51]

...classic example of what one can make with just the junk lying around in a reasonably junk-fertile shop.
Anyone see a pattern?
...ingenious bearing clamps made from screws, washers and spent 0.22 cartridge cases for spacers.
.....lucky to have an 18:1 planetary gear assembly lying around
......components rejected from a spacecraft antenna pointing mechanism and I retrieved it from the dumpster.
........two discarded steam chests I made for one of my steam engines.

All I can say is LoL and Marv deserves another round of genuine applause.



And Stevodee observes "Junk is just material waiting to be used, nice build ". Same here, but my phrase runs "it's only scrap when it's too small to hold"

[Frank S]

[DIYer]

Thanks mklotz! We've added your Transit to our Measuring and Marking category,
as well as to your builder page: mklotz's Homemade Tools. Your receipt:

Transit by mklotz

tags: protractor, measurement

[mklotz]

And Stevodee observes "Junk is just material waiting to be used, nice build ". Same here, but my phrase runs "it's only scrap when it's too small to hold"

Exactly!

My rule for saving offcuts is: it doesn't go in the scrap bin until it weighs less than a nickel (5 grams).

[PJs]

Excellent build and "Story" Marv, definitely a fine scrap build. Funny I have 2 of those same protractors, one in my drafting template box and one bench handy and they came from a great stationary store back in the day!

Scrap Story...Back when, I used work across the street from ILM and our machine shop was next door to them. That was some of the best dumpster diving ever after getting to know a couple of people there. A month or so after a production one of my buddy's would let me know...it's time. Funny though almost all of them were hoarders by modern definition and had pallet racks and mobile racks of reusable stuff from projects, inside the building and what got tossed or not taken home made it to the dumpster, mainly for room...but still the diving was the best ever! I can imagine NASA bins would be the next level!

As for size/weight I have multiple film containers full of tiny shim stock, acrylic, AL and SST pieces and actually use them sometimes on tiny projects and often find just what I need with out having to take something tiny from a larger piece.

Thanks for the great build and story Marv!

PJ

[Papa Smurf]

Excellent build, Marv. Fit for purpose made from whatever is to hand.

Now for the hi-jack:

I have a question that someone on this group may be able to shed light on:

What accuracy is expected of the bubble level on a professional surveyor's transit? Let's confine ourselves to pre-digital technology. I'm curious because I have an antique instrument and wondered if it could be put to use levelling a lathe bed? Obviously we're bordering on the discussion around the length of a piece of string, but there must be someone who knows how level the surveyors needed to set their instrument before they could measure an angle from their plane of reference.

Interestingly, both my paternal grandfather and one of my uncles were surveyors, but both of them died when I was a schoolboy.

[mklotz]

Excellent build, Marv. Fit for purpose made from whatever is to hand.

Now for the hi-jack:

I have a question that someone on this group may be able to shed light on:

What accuracy is expected of the bubble level on a professional surveyor's transit? Let's confine ourselves to pre-digital technology. I'm curious because I have an antique instrument and wondered if it could be put to use levelling a lathe bed? Obviously we're bordering on the discussion around the length of a piece of string, but there must be someone who knows how level the surveyors needed to set their instrument before they could measure an angle from their plane of reference.

When discussing levels, the evaluative term is "sensitivity", not accuracy. Sensitivity is normally expressed as the smallest angular deviation the level can detect.

The Starrett 98...

https://www.amazon.com/Starrett-98-8...ds=starrett+98

often used for lathe unwinding* says it can detect 4.2 mm/m of deviation, which equates to...

3600*arctan(4.2/1000) = 86.6 arcseconds

This is undoubtedly more sensitive than the typical transit level.
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* A lathe bed need not be level; what's important is that it had no twist or "wind" in it. A convenient way to test for wind is to apply a level along the length of the bed. If the level shows no deviation, the lathe bed has no twist.