Scientific Instrument fabrication

[Homemonkey]

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
http://i96.photobucket.com/albums/l167/locostmonkey/1370Astrolabe013.jpg
or just about any of these
http://i96.photobucket.com/albums/l167/locostmonkey/MultipleInstruments014.jpg

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

[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. . .

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

[Evan]

See here:

http://www.geocities.com/richardandtracy/SextantPage1.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.

[aostling]

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?

[PTSideshow]

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.
:D

[Evan]

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?"

[Fasttrack]

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

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!

[SHADOW]

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.

http://img146.imageshack.us/img146/8087/astrobg9.th.jpg (http://img146.imageshack.us/my.php?image=astrobg9.jpg)

[ckelloug]

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

--Cameron

[BobWarfield]

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/cnccookbook/CCOrreryNotes.html

and a drawing or two:

http://www.thewarfields.com/cnccookbook/img/Antikythera/ZodiacPerspective.jpg

http://www.thewarfields.com/cnccookbook/img/Antikythera/OrreryPersp.jpg

Cheers,

BW

[oldtiffie]

See here:

http://www.geocities.com/richardandtracy/SextantPage1.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.

[Evan]

I had to wait until I had some way to engrave it. Now I do.

[GNO]

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 !!!

[Homemonkey]

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:D

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

[Homemonkey]

See here:

http://www.geocities.com/richardandtracy/SextantPage1.htm



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

Eric

[Homemonkey]

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/

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.
:D

Glen thank you. I was aware of Lindsay books and have ordered a few from them over the years. I had never heard of astragal press, It looks like another valuable resource.

Also, thanks for the info on cutting by hand. So starting from a flat sheet, scribe somehow the overall form, cut outside the line and file away - makes sense. I've asked this in an earlier reply (a few minutes ago) but regardless if I cast or cut from flat stock, how would you guess the precision "degree" mark and other arcs are added?

Perhaps there is much less machine work than I suspected.

Eric

[Homemonkey]

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.

http://img146.imageshack.us/img146/8087/astrobg9.th.jpg (http://img146.imageshack.us/my.php?image=astrobg9.jpg)

Shadow,
Thanks for the reply. I have that book as well as the Scientific Instruments book that appears in your pic. I'll have to look into getting the others. What are the titles of the others in the background? Are they the ones from astrgalpress?

Making lenses that function is something I might try in the future (I am a glass artist and have an old book on it) in the meantime, I would probably just make various glass parts that fit.

Thanks,
Eric

[Homemonkey]

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

--Cameron

Great - and there are links there to the actual text.

Thank you,
Eric

[Homemonkey]

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

http://www.thewarfields.com/cnccookbook/CCOrreryNotes.html

BW

Bob,
Your project is fantastic. Most of it is beyond my current comprehension, but i absolutely love learning about the same sorts of things you discuss and have links to.

So will everything be CNC'd? All of the zodiac names etc. Or are there places that you will use some sort of hand scribing?

Also your site is just the sort of thing I've been looking for. Lots of information to try and digest.

Thanks,
Eric

[BobWarfield]

Bob,
Your project is fantastic. Most of it is beyond my current comprehension, but i absolutely love learning about the same sorts of things you discuss and have links to.

So will everything be CNC'd? All of the zodiac names etc. Or are there places that you will use some sort of hand scribing?

Also your site is just the sort of thing I've been looking for. Lots of information to try and digest.

Thanks,
Eric

No hand scribing, I've neither the skill nor the patience to learn! It will all be CNC. Most of the needed designs are actually very 2 1/2 dimensional. By that I mean they are not elaborate 3D carvings. They should be straightforward to CNC. Brass machines beautifully, so that will be nice too.

One other skill I want to learn more about is enameling. I envision that as the ideal way to add color to the proceedings, although you can also do inlay with CNC.

Speaking of CNC inlay, sometime you should look into what custom guitar makers can do with that. It's amazing.

So, if you sacrifice yourself at the altar of CNC (lots of learning curve, lots of costs, lots of time), you can do all that. You shouldn't even need casting--curves are easy in CNC.

Get hold of a copy of Rhino3D and try drawing some of those old astrolabes and such. If you can draw it, you'll eventually be able to CNC it.

Cheers,

BW