Plate clock movement – simple but finicky

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German-made time-only plate clock movement

Small shelf clocks of the 1930s from BlackForest Clock Co. of Toronto shared a simple German-made time-only movement across the line. The movement has tiny wheels and pivots plus a clever twisting pendulum rate adjuster.

Blackforest shelf clock, the case has been stripped (previous owner) but it manages to look attractive

I must have a place in my heart for these small clocks as I now have three. Two are now in running order while the third is a parts clock.

The mainspring is the movement’s weak point and in two of the three, the mainsprings were either broken when I received it or broke shortly thereafter when I attempted to let it down.

The second wheel evidently bent when the spring let go, so, thankfully I had a spare
The mainspring is broken but the movement reassembled to keep everything together while I order a new mainspring

These movements should never be overpowered. Should the mainspring require replacement it must be the same strength. The width, thickness and length of the new mainspring must match the old one precisely. After measuring I ordered a new one through my supplier.

I was unable to use my spring winder to install the mainspring into the clock housing and had to resort to coiling the spring into the open barrel by hand. It is not as difficult as you might think but wear work gloves for an extra measure of safety.

My non-working spare movement is for the parts. The escape wheel had a few nicked teeth and I took the one from the spare. I also replaced the second wheel which was bent when the spring let go. With a replacement escape wheel, second wheel and new mainspring I am ready to reassemble and begin testing.

During reassembly, care must be taken not to damage the tiny pivots. A pivot locator should be used as the pivots should not be forced into position. There are very few gears and everything clicked together nicely.

Top of movement showing adjustment screw, steel pivot and cup

These movements must be perfectly level to operate and must be in beat. At the top of the crutch sits a pointed steel pivot point that rocks back and forth in a cup. It and the cup must be perfectly clean and are not lubricated.

The beat is adjusted by twisting the verge on the arbour to find the correct entry and exit of the pallets. The height of the verge is adjustable by a screw located under the arbour, clockwise raises the verge and counterclockwise lowers it. A slight turn of the screw is all that is necessary to find the correct height however it can be difficult to get it right the first time. Success comes when the beat is steady and the pendulum amplitude is strong as you can see in the short video above.

Blackforest shelf clock
Another Blackforest shelf clock, a 1937 commemorative edition Royal Visit shelf clock

It is a well-engineered movement in a cheap pine clock case with a lacquered walnut finish. These clocks were inexpensive in their day and were often discarded when they stopped but there is no reason why this one and others should not run reliably for years to come.

Although simple in design and function they are a pain to get right.