Kemenyek: Smiths chronometric instrument drives.................

In an earlier Blog I discussed Smiths tachometer drive gearboxes.
This blog discusses the small 90 degree instrument drive gearboxes that were fitted to the Smiths chronometric speedometer and tachometer. As well the later BG2410 series drives that were a thumb screw attachment to Smiths speedometers to get a more suitable cable run in Rover 2000 and 3500 P6 cars and Jaguar XJ6 cars in the period mid 1960-end 1970.
Left click on any image to enlarge it....
The first pic is one that perplexes me....
You'll note it is a 250MPH speedometer in 80mm dia. format...wow!
I obtained this with the stock of the ex Smiths Competition Shop, Oxgate Lane, London, that I bought in the 1980's from the last manager, the late Jack Owens.
I never questioned him over it's use regrettably....so now I figure it could be off a Le Mans endurance racer, note the black bezel rim to cut reflection rather than the usual chrome version. To this day we can't identify it....
H'mm....
Well new information to light from Rodger Howard of Howard Instruments in Melbourne, Victoria to whom I sold the speedo to.
He chased up it's history and it is from a 1966 Jaguar XJ13 Le Mans racer

You'll notice that it has the small angle drive, attached by a keyplate to the case.

The method of attachment is shown...you'll notice that the internal die-cast frame that holds the movement mechanism has no threaded section with mainshaft, rather this is all in the small drive.
So the other drive, mentioned above is a clamp on type Smiths drive..illustrated below.

Illustrated is an assembly of both keyplate and clamp-on drives in parts...

I mentioned above the three types...illustrated below, beside each other.

The BG2410 series has several attachment methods , illustrated as well as in parts. We tooled up to make these years ago and still make and supply them.