Identifying WT C40B & C movements.

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There was an ongoing discussion on WT model designation [letters C40A, B & C] in the comments section of my blog when  a new example appeared at auction.

The C40B, recently sold at auction, has matching 'shoulders' and the larger wormwheel of the larger models. A new detail has been raised to confuse the issue. On the right of the mainframe there is a clear step in the casting. While the much larger C40C drops straight down to the cast foot without such an obvious step.

These Gents factory drawings show the different models.

The C40B mainframe [image right] has matching shoulders but they slope slightly. While the shoulders of C40C  are more "muscular" and are horizontal where they meet the pendulum support bearings. [image below]

Judging mainframe size from online images is certainly not easy. Another point of confusion lies with the later chair-frame models using the parlance of weight-driven movements. Though in the case of the later WTs the frame is stepped sideways. Rather than from front to back. L-shaped frames might be clearer than "stepped" frame. Since the model B does seem to have a step of its own. One not shared by the C40C.

However, a glance at the only example of an early C40"C" on Clockdoc.org clearly shows a step on the right of the mainframe:

https://clockdoc.org/?user=European&moid=53980

In fact this example easily satisfies the description and appearance of a C40B. Stepped on right of frame and matched, sloping shoulders. A nice example too!

Each larger model in the WT series is supposed to drive the hands of larger dials than the next smaller. This strongly suggests a change of scale is required. Scale brings stronger drive electromagnets, a larger drive wormwheel and heavier pendulum.

These are only the most obvious "bigger engine" details required to increase torque beyond that available from the smaller models. Some models of WT show much larger time setting dials and matching, larger bevel gears. Surely an obvious clue to the greater expectations in driven dial size?

Discussion of these details is not mere horological pedantry. The larger models are vitally necessary beyond a certain dial size or number of larger dials. The theft of a much rarer, C40C from the Terry's factory meant that no replacement could be easily found. A national appeal went out to interested parties within the clock milieu to find a replacement.

A smaller model  of WT will be found wanting in driving and controlling the much heavier hands of larger dials. Adverse weather will soon show with an under-powered WT. A row of birds will unbalance the hands. Ice and wind loads rise alarmingly with hand and dial size.

Larger dials [and their much larger hands] will usually be installed much higher on highly exposed buildings. Small dials are quickly lost with distance. Rapidly shrinking into insignificance. The general rule is that a dial diameter should be one foot in diameter for every ten feet in installed height on the tower or building. Not always achieved due to architectural restraints but worth adhering to.

In the next [newer] post I shall show some images of these larger WT models culled from the Internet for educational purposes.

Click on any image for an enlargement.

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