Sine Tables, Sine bars and calculations

Hi All

An interesting sine table

Made by Matrix Tool and Gauge Coventry England

The hypotenuse is 5 inches

With the top of the table level in both planes the gage block height for each axis is 3.75 inches. To set the angle or angles you place a stack of gauge blocks under the two spherical pins.

For a minute I wondered how the large radius could relate; the answer being an imaginary ball in the centre. The axis of the two small spherical locating points, located at 90 degrees to each other, pass through the centre point of the large ball segment. So as the large ball rotates the imaginary ball in the center and the two locating balls rotate also. Maintaining the strict 5 inch relationship to the two visible balls,

All that remains is to constrain the vertical axis. This is done by the 90 degree plane formed in an arc around 90 degrees of the large ball.

What I like about this design is the immense strength. Once set the large ball is locked into a cast iron pocket buy a single bolt that pulls the ball into the socket. There is a spherical coupling at the geometric centre of the large ball.

It is nice to see a design based on first principles.

I have no idea what the two small pins seen in the photo showing the vertical axis constraint do? The must have a use. Does anyone know?

I have no documentation for this find and would appreciate any feedback.

 

Cheers

 

John McNamara

 

Edited By John McNamara on 08/05/2011 03:06:31

Edited By John McNamara on 08/05/2011 03:33:21

John - I can foresee a sort of problem. The small pins that you point out may be there to stop the big ball from over rotating so you will not get the small balls up on the table. Hum Ho