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machinist - [machinist] The Newbould Indexer - the 28th basic mechanism in the Smithsonian - several explanations of how it works.

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  • From: Lawrence London <lfljvenaura@gmail.com>
  • To: machinist@lists.ibiblio.org
  • Subject: [machinist] The Newbould Indexer - the 28th basic mechanism in the Smithsonian - several explanations of how it works.
  • Date: Mon, 25 May 2020 00:57:19 -0400

Information gleaned from several machinist forums:

[]

How I think it works is like this, it has three sets of face gears. I guess they are just V shape and it is akin to a dog clutch type sort of thing. On one set the pitch between the teeth is 1 degree. That is move one gear one notch moves it one degree.

Now the next gear set the tooth pitch is one degree and one minute. But this has a dilemma that the last tooth is a tiny tooth which is OK when it fits in the mating gear as it is cut the same, but it will not fit anywhere else. So the solution was to remove the next tooth on one side, then the next, removing 60 teeth from one gear.

Then you cut the next gear set. It is one degree, one minute and one second between teeth. And the same again, you end up with a dodgy tooth at the end, so cut out another 60 teeth.

So you want to index one degree one second. So you move the first gear set clockwise two notches or two degrees. Then you move the third gear set backwards one tooth or one degree one second. So you have moved forward one degree one second.

The reason to cut out sixty teeth out of the two gear sets is once you move either of the two sets 60 teeth, you have moved either a full degree or a full minute but it leaves plenty of teeth to engage for locking together.

[]

It indexes every 8 degrees.

The top pitch is 24 degrees, making 15 teeth

The bottom pitch is 16 degrees making 22.5 teeth. Odd tooth is marked in red.

Difference = 8 degrees.

Starts closed at zero degrees.

Opens, indexes middle "adapter" disk one pitch of 16 degrees.

Closes, top plate forced to rotate 8 degrees to engage.

Repeats until end of clearance area, totaling 24 degrees rotation of top plate.

Middle plate returnes to start position, top plate stays at 24 degrees.

Repeating would index another 24 degrees to total 48 degrees

This means the adapter plate goes back and forth in the open area and effectively ratchets the top plate in 8 degree increments.

Make the adapter plate free rotating, and you can set any 8 degree angle at random.

Change pitches to suit for desired increments.

[]

Video on You Tube

https://www.youtube.com/watch?v=3EGGuR5YziE

listed as the 28th basic mechanism invented

Published on Jan 3, 2017

A model of the Newbould Indexing mechanism as invented in 1971 by Richard Newbould. Used for quick and accurate direct reading angular indexing. Is listed as the 28th basic mechanism invented. A description written by R J Newbould of the model shown is as follows;

It indexes every 8 degrees.

The top pitch is 24 degrees, making 15 teeth

The bottom pitch is 16 degrees making 22.5 teeth. Odd tooth is marked in red.

Difference = 8 degrees.

Starts closed at zero degrees.

Opens, indexes middle "adapter" disk one pitch of 16 degrees.

Closes, top plate forced to rotate 8 degrees to engage.

Repeats until end of clearance area, totaling 24 degrees rotation of top plate.

Middle plate returnes to start position, top plate stays at 24 degrees.

Repeating would index another 24 degrees to total 48 degrees

This means the adapter plate goes back and forth in the open area and effectively ratchets the top plate in 8 degree increments.

Make the adapter plate free rotating, and you can set any 8 degree angle at random.

Change pitches to suit for desired increments.

[]

See OxToolCo's youtube Monday Night Meatloaf #115 near end for the Newbold Indexer model 202 that is the production model- single arc seconds of division.

--
Lawrence F. London, Jr.
lfljvenaura@gmail.com
Avant Geared
walnut and oak serving and kitchen cutting boards
https://sites.google.com/site/avantgeared
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  • [machinist] The Newbould Indexer - the 28th basic mechanism in the Smithsonian - several explanations of how it works., Lawrence London, 05/25/2020

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