Back Up Next

Maker Charles MacDowall, Wakefield, England, c. 1830 - 1835, s/n 169. 4.25"w x 9.75"h x 4.25"d net of base and dome. Deadbeat escapement, one month duration.

There are several novel features employed in this movement. The pallets, together with the crutch, are pivoted between the frames. Therefor no separate pallet cock is used. The crutch, fashioned from flat brass is unusual in having a slotted curved aperture suspended from a triangular section and swings between the helix escape pinion. The fork then protrudes through a slit cut into the frame to meet with the pendulum. Wheels are made of bronze in which the helical tooth pattern is cut. Due to the fact that helical wheels cause considerable side thrust, there are end or pivot screw caps throughout the train and the frame is thick at just under 1/4" thick. The barrel cap is held by three screws rather than press fitted.

All of his clocks were numbered and came in two basic frame styles. These however were individualized with some changes in the frame, pillar, dial or crutch details. This example is the only one known to employ maintaining power.

It is unknown if MacDowell was the first to employ helical gearing to clocks, but he was the only person to ever produce commercially a clock with complete helical gearing and helix pinions.

MacDowall (1).JPG (1068036 bytes)  MacDowall (2).JPG (1084016 bytes)

                                                            MacDowall (4).JPG (1030238 bytes)

                                                           MacDowall (11).jpg (275335 bytes)

The word helical is derived from the Greek and may be translated as 'having the form of a spiral'. In helical gearing a spiral groove is cut in the arbor or pinion which meshes with teeth angled to match it. It has these advantages: a) Power is transmitted by pressure and rolling without any sliding friction. b) The contact bearing area is increased, enabling far heavier loads to be dealt with smoothly, but this consideration is not normally of importance in clockwork. c) A much greater reduction in gearing may be achieved than with conventional wheel and pinion. (If the length of a spiral, for instance, which produces one turn of the arbor is equal in length to one of the teeth with which it meshes, then every tooth on the wheel will rotate the arbor once. Thus if the wheel has fourty eight teeth, the arbor will rotate fourty eight times whereas if a conventional wheel of fourty eight teeth meshes with an eight leaf pinion the arbor would rotate only eight times.)

The practical application of this in horology is that either one wheel and pinion may be omitted from the train, longer duration may be achieved, or some combination of the two, but in practice it is doubtful whether it is of any appreciable value. Helical gears because of their high ratios, absorb more power than a conventional train even with an extra wheel and pinion, and the complex machining required to cut them, utilizing both rotary and a progressive action, makes them far more expensive to produce. A further disadvantage is the lateral or end loads which helical gears impart to a train which is one of the main causes of power loss in a clock and is why end caps need to be employed on the train.

Whereas in horology the disadvantages of helical gearing far outweigh the advantages, in general engineering it has been used extensively, virtually since the start of the Industrial Revolution, in gearboxes and power transmissions of all kinds where a heavy load is to be expected. (1)


Back Up Next

(1) British Skeleton clocks, Derek Roberts, pp.171-172