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  • Scientific Instrument fabrication

    Hello,
    I'm new to the forum and NOT a machinist (yet) and have some questions, and some assumptions. Please forgive any blatantly wrong assumptions.

    I would very much like to first, understand the processes used to create old scientific instruments like astrolabes, quadrants, nocturnals, armillary spheres sextants, etc., and second build some replicas at home in my garage (Manspace).

    I have almost no machining experience other than a few small pieces turned on a lathe. I assume that the majority of these instruments parts were created using a lathe, mill and some sort of mechanical engraver.

    I am hoping that somebody knows of some books, plans or other forums that would help me get started in creating things like this

    or just about any of these


    Once I have an idea of the process, I can begin to acquire the right equipment. I'm assuming there is some sort of multi-machine combo that would be fine for me (less expensive than a pro needs).

    Anyway, any help is greatly appreciated.
    Eric

  • #2
    Do you want to duplicate the process by which the old instruments were made or do you wish to just make the instruments? I suspect that much of the work in the old instruments was done by hand and by sand casting via processes that are involved. Think hand filing. . .

    To make functioning replicas, I suspect you should be able to do so with a mill and a lathe. There are not a lot of fans here of the 3-in-1 machines due to precision issues and the extra work they create but I'd suspect one would be serviceable for your application.

    Good luck, old instruments are interesting.

    --Cameron

    Comment


    • #3
      See here:

      http://www.geocities.com/richardandt...xtantPage1.htm

      I have been saving this project for when I finished my cnc mill. It seems like a nice design and not too hard to build.
      Free software for calculating bolt circles and similar: Click Here

      Comment


      • #4
        Evan,

        My brother gave me an "atomic clock" for Christmas. It cost less than $8. But it receives a time signal, and I guess must be accurate within a second. With that as a chronometer, and with this sextant you plan to build, how close could you determine your position, anywhere on the earth?
        Allan Ostling

        Phoenix, Arizona

        Comment


        • #5
          Here are a couple of places that may have some books to help you along. They have mostly reprints of the old style do it your self books.
          http://www.lindsaybks.com/
          http://www.astragalpress.com/
          Lindsay has a book on making electrical instruments the old style stuff. Astragalpress also has a number of books you my find of interest.
          Most of the work would have been done with casting or cut from flat stock. You would need a good assortment of files and a couple of jewelers saw frames of different depths from frame to blade and an assortments of sized blades for said frames. along with the general hand tools and a drill or drill press. You also can braze and grind down file separate pieces into one unit.To build up the frame shape or other pieces if you don't want to cast them. A lot of items are made in the home shop that way. Only some people wouldn't tell you they took a short cut like that. Depending on how you feel about modern equipment. You probably can get by with the small table top equipment
          http://www.sherline.com/
          is one type I happen to own a mill and lathe and like them a lot.
          Glen
          Been there, probably broke it, doing that!
          I am not a lawyer, and never played one on TV!
          All the usual and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or the suggested uses, Wear safety glasses, closed course, professionals only

          Comment


          • #6
            Back in the early 80's I wrote a celestial navigation program that calculated the apparent position of the sun in the sky instead of using precalculated ephemeris tables. To do so requires the consideration of at least 20 to 30 periodic perturbing, nutating and other cyclic terms. To be really accurate requires the consideration of over 100 terms that are a result of every piece of matter orbiting the sun and consequently affecting the orbit of Earth. My program was able to provide 1/4 mile accuracy and fit into the 4k of ram in a Commodore VIC-20 which conveniently runs on any ac or dc source of 12 volt power.

            A sextant sight doesn't provide you with an exact position. It provides you with a line of position (LOP) along which the same result will be obtained at any point at a particular time. Note: a local apparent noon sight is an exception, the possible LOP is directly north/south. To make a fix requires a second sight at a later time. Then the crossing point of the lines of position can be determined. How accurate this is depends on the time interval between the sights. The shorter the interval the shallower the angle the LOPs cross at the the less determinate the fix. Also, there are two possible places on Earth that will provide the same resultant with the same second LOP so the longer the interval the less the uncertainty about which position you are really at.

            As for the time element, a one second error in sight determination amounts to about 1/4 of a mile of error at the equator diminishing in proportion to increasing latitude.

            The bottom line is that with a tripod mounted manual sextant of the best sort in a fixed position on land and perfect observing conditions with multiple observations over the period of a day using a perfectly accurate clock (whew) one might expect an accuracy of position to within a few hundred feet, depending on the skill of the observer. At sea on the heaving deck of a small vessel the best that can be expected is to place your position within the distance it takes to see land masses on the horizon, if you are within sighting distance.

            That is why other navigational techniques are used. The old ploy used by experienced navigators (I studied celestial navigation when I obtained my pilot's license) is to ask a newbie where is is after flying for some period of time. If he plunks his finger on the map without hesitation then you say " you are lost, aren't you?"
            Free software for calculating bolt circles and similar: Click Here

            Comment


            • #7
              If you can swing it, please, for the love of God, don't buy a three-in-one!

              There are fans and non-fans here of the combo machines, but after having used the real deal, coming back home to my three-in-one is ... well painful.

              I've used several bridgeports of varying degrees of wear and an around-the-world sample of lathes including a cincinati (America) and Harrison (UK) and an MSC (china) and while my three-in-one lathe works pretty well, the mill plain sucks. I've found it to be flimsy and extremely limited in movement especially for any projects that require steel or cast iron to be machined. Also, my dials are graduated with .002 between lines. This sucks - you can only get to within +/- .0015 with the dials which isn't really that good. If you try to mill a slot down the middle of a shaft or something often times you find that you have to move a distance of 0.XX1 and not being able to move that last thousandth accurately will make a noticeable difference in whether it appears to be centered or not.

              I was always happy with my machine until i started using the real deal and now i see just how time consuming and frusterating the three-in-ones are!!


              Just my .02

              Lots of other opinions out there so listen to as many as you can stomach () before making any decisions!

              Comment


              • #8
                I would suggest the book "Latitude Hooks and Azimuth Rings" by Dennis Fisher. Simpler versions of instruments, mariner's astrolabe, quadrant, octant, nocturnal, etc. Although done in wood in the book an upgrade is certianly possible. If you're really set on a full blown astrolabe I believe Chauce's writings in the original old english are available with drawings, although it takes a while to read. a number of instruments from the scientific instruments book need lenses for the optical path and increases the effort.

                Comment


                • #9
                  You mean Geoffrey Chaucer's A Treatise on the Astrolabe? http://en.wikipedia.org/wiki/Treatise_on_the_Astrolabe

                  --Cameron

                  Comment


                  • #10
                    I'd be looking at CNC to do stuff like that unless you have a lot of art skills in your fingers.

                    I have an interest in creating something similar, an astronomical clock. It's way down my list, but I have done a little research into it:

                    http://www.thewarfields.com/cnccookb...reryNotes.html

                    and a drawing or two:





                    Cheers,

                    BW
                    ---------------------------------------------------

                    http://www.cnccookbook.com/index.htm
                    Try G-Wizard Machinist's Calculator for free:
                    http://www.cnccookbook.com/CCGWizard.html

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                    • #11
                      Nice surprise

                      Originally posted by Evan
                      See here:

                      http://www.geocities.com/richardandt...xtantPage1.htm

                      I have been saving this project for when I finished my cnc mill. It seems like a nice design and not too hard to build.

                      Well Evan.

                      You really are full of nice surprises.

                      Using it will be a fine test of many skills - particularly if used in a boat or a small ship in a significant sea-way!!

                      I don't doubt for a minute that you can and will make and use it to your usual very high standards of achievement.

                      Comment


                      • #12
                        I had to wait until I had some way to engrave it. Now I do.
                        Free software for calculating bolt circles and similar: Click Here

                        Comment


                        • #13
                          metal parts

                          something to look into--lost wax casting. that is how jewelery, turbine blades,some gun frames are made.it is so sensative/accurate that it will pickup fingerprints !!!
                          geno

                          Comment


                          • #14
                            Originally posted by ckelloug
                            Do you want to duplicate the process by which the old instruments were made or do you wish to just make the instruments? I suspect that much of the work in the old instruments was done by hand and by sand casting via processes that are involved. Think hand filing. . .

                            Good luck, old instruments are interesting.

                            --Cameron
                            Wow, this is one active forum. Other forums I've visited might have one reply by now, not 2 pages

                            I am most interested in "just making the instruments." I figured that some of the more "organic" parts were lost wax cast, and in some of the pictures I've seen, you can see a rough gritty texture where the sand was not packed properly.

                            Are you suggesting something along the lines of doing the majority of the work in wax and perhaps leaving some extra thickness to sand/file/mill down to flat? I have experience in lost wax casting of bronze (I teach glassblowing and sculpture) so this would be a possibility.

                            For the astrolabe (top pic) I assumed that the "degree" marks were made on some sort of indexed engraver (my term - don't know the lingo yet) and had no idea on the various arcs in the background. It seemed to precise to be scribed by hand, but what do I know? If they were scribed by hand, what would you need? A diamond or hardened steel scribe and various compasses, rulers,french curves etc?

                            Thanks,
                            Eric

                            Comment


                            • #15
                              Originally posted by Evan
                              That is fantastic Evan, thank you very much - exactly the type of thing I need to bookmark and work my way up to!

                              Eric

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