This is a telegraph sounder described in a boy's construction book, pre WWI.
It works very well, but tricky to make as the instructions lacked measurements and detail. I found there was too much play in the pivot, so added a guide, a vertical rod through the moving arm, which stopped it jamming. A better pivot with a bearing would help, even a rod through a metal tube.. I hadn't understood that if the steel plate on the arm touched the top of the magnet, residual magnetism would hold it there and it would also stick. A lot of adjustment was needed but once right it works reliably. 200 turns on the coils, maybe 20swg, wound on a 2 inch bolt, 1 inch high. Apologies for the morse - it is gibberish. Base board 10 inches long. I love the clunking sound, far nicer than a buzzer.

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