Was this the birth of CNC ?

[Michael GilliganParticipant @michaelgilligan61133]

Neil,

There are some useful notes and references here:
http://www.cnccookbook.com/CCOrreryNotes.html

MichaelG.

[Richard ParsonsParticipant @richardparsons61721]

Billy I will agree with you about the wheels on the Home Pointing Chariot. The Chinese were very good craftsmen. They knew about both the Compass plane and the lathe so there was no problem over wheel sizes. The main cause of errors with the chariot was bumps in the road, but these generally averaged themselves out. The chariots would be deployed in ‘foreign’ or ‘enemy’ territory.

They used lodestones yes but they did not understand the problems of Magnetic Variation. which is something the Hungarians do not know either.

Have a look at the Beijing Ancient Observatory. Although this place is quite late on, the mid 1400s, it was very accurate. It had one of the world’s first seismographs for providing the authorities with information about earthquakes (for disaster relief). Its main use was for providing accurate information for astrological.

The chariot could be (and probably) was re-aligned by either the noon day sun or Polaris. One should remember that 20 miles was a long day’s march and that a rapidly advancing army would make on average only some 6 to 8 miles per day.

Rgds

Dick

[Billy MillsParticipant @billymills]

Dick,

I’ve seen the astronomical exhibits at Beijing, been there, stood on the roof. Very impressive, there is also the very long period of recorded observations at Beijing. However it pails compared with the Great Wall. We tried walking along the wall during a local public holiday, half of China was up there that day. Sharpened elbows honed on the London Underground were very helpful as was being an Ugly outsider somewhat taller than the locals. The Wall takes the most difficult route possible up hills and down slopes, much of the Wall is in good condition.

 

The “Seismograph” is really only an indicator of movement, although it was claimed to be directional that is perhaps a triumph of hope against reality. But it did have a suspended mass.

 

The ancient world did have a lot of trackways- which tended to get well rutted- so I would not want to depend on differential rotation of wooden cart wheels on a trackway or averaging rock hits out.

 

Thanks for the Antikythera reconstruction link, there is also a 3D model on http://www.mogi-vice.com with a video on the tube following your link. However the use of the term Computer is perhaps misleading, Calculator is more appropriate. It remains a great achievement for the period, all of those different gears!

 

Billy.

Edited By Billy Mills on 16/12/2011 13:28:46

[Richard ParsonsParticipant @richardparsons61721]

Billy you are right the Antikythera was a mechanism to replicate planetary motion and to provide corrections to sundials used to set the public water clocks. It is not the only example of such an apparatus in existence. There is Richard of Wallingford’s celestial clock, which he never finished, but has been made as a modern replica. There is also the great clock in Prague and hordes of others. None of these are computers in the true modern sense of the word but are mechanical simulations of the situation as we understand it. It of course is incomplete in the same way that when you think that float glass is flat. It is not as I learned when I used a piece as an optical flat in an 8” Newtonian telescope. Float glass is actually a spherical whose radius is that of the earth where it was made.

I had fun once with the corrections to a form of gyroscope. This thing was mounted on a large steel tube which went down into the bed rock. It used to display movement and seemed to be slowly moving in one direction. They had taken the earth’s movements around the sun but had forgotten earth’s precession or the earth orbit round the sun and the wobble of the earth’s axis. My programmer had the vapours over that one. The corrections were added to the program but it still showed drift. Not acceptable to the customer. I had to do a lot of digging into astronomy and found that the sun its self was moving through space. New corrections were added and the thing settled down to be within the experimental error. The customer bought the system but not the program. We can write that ourselves they said. Result -2 years later the sued us for the program specification and lost the day. The bought at a huge cost both the program, its specification and support from the Executive in Electronic Information Organisation. Yes assistant analyst was the EIEIO!

[Billy MillsParticipant @billymills]

Richard, I was wondering how the gears were made in ancient times. The Antikythera needs a lot of well formed gears to run at all smoothly. Perhaps the main tool would be a tapered edge file and we could assume a simple lathe was available so how could it be done? Perhaps you could make an equally spaced rack by marking an edge with a small rotating roller with a notch. By inking the roller you could evenly mark the edge then file rack teeth into the edge. A disc could be turned then marked with the roller and the marks counted, the diameter could then be turned or filed down until the right number of marks was around the circle then you file teeth gaps into the circle using the rack as a meshing gauge. Now this would not work because you would be marking the outside diameter not the pitch circle however you could correct this by having a very slight taper on the roller so that the marks were slightly further apart making the bare disk larger. or by over cutting the teeth.

 

How did they do it?

 

Billy.

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