I have another Cuckoo in the shop this month; this one is an original Black Forest Clock with a cuckoo>>>>>>>>>>>>>>>>. The movement - upon first glance - looks like a amateur birdhouse project gone wrong. But there is beauty here beyond one's initial dismissal...... I believe the wood frame is beech; the pivot holes are brass bushings. This is really the ultimate in practicality: using the materials that are most abundant (and most likely right outside your door!!). Once you spend some time with the movement you really can appreciate the concept here: everything makes perfect sense and operates just as perfectly. When you work in metal for so long you assume tight tolerances and rock-solid construction are foundations of unfailing consistency over decades of constant use. But here we have a 130 year old shaky wooden cage doweled and pinned together, and worn brass bushings that all appear to be the originals. The gear fit is loose at best - yet both trains operate without a hitch.
The best part? Each train of gears is removed by unpinning one of the wood posts in the back of the movement, so if you need to make an adjustment to the strike train the time train will remain in place during adjustment. Sweet design!!!!!
The bad news? The small pinion that drives the count wheel on the back of the movement is missing. >>>>>>>>>>>>>>>>
The tricky part here is deducing how many teeth the drive pinion should have; once we know that then we can work out its diameter. The pinion is to be staked onto the extended arbor of the strike train ratchet wheel. This ratchet wheel also carries 11 pins which lift the cuckoo and hammer levers. The count wheel has 90 teeth (1 for each time the clock must cuckoo & gong during a 12 hour period). By design, one segment of a call (1 gong and 2 cuckoos) is carried out by the ratchet wheel travelling the distance of one pin (or exactly 1/11th of a turn in this case). This is enough motion to lift all 3 levers once and stop. Thus, we want to exactly reflect that ratchet wheel pin movement onto our pinion drive which will advance the count wheel exactly 1 tooth for each segment of a call. This means that we need to make an 11 tooth pinion gear.
I found the easiest way to accomplish this is to use a long brass rod which can be held in a collet or chuck with the end turned down to the correct diameter and center drilled to fit the arbor. The whole rod can then be brought from lathe to indexer (here I use the rusty 4-jaw chuck to hold the rod for indexing>>>>>>>>>.
The 11 tooth gear is accomplished via direct indexing (simply dividing 360 degrees by 11 and advancing by that number (32.727272) after each cut.
After the profile was created on the pinion the rod was moved back to the lathe and the pinion was parted from the rod. Unfortunately, the first attempt was thwarted at parting - one of the pinion teeth broke off. So back to the beginning we go.
The bottom photo shows the finished pinion ready to be staked onto the ratchet wheel arbor, and it's cousin with the broken tooth. >>>>>>>>>>>>>>>
"Don't make me go out there again!!!!!!"
Brass stock held in 4-jaw chuck mounted on dividing head. Initial pass taken with 1/16th" slotting saw.