August 2011
Black Forest Cuckoo With Wood
Post Movement
A Monthly Sample of Clock Repair Projects
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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.
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See Other "In the Shop"

Boardman & Wells Wood
Works Shelf Clock

Ithaca Double Dial

Black Forest Cuckoo

Cuckoo with Quarter

Scottish Tallcase

Kienzle Clock Restoration

London Dial Restoration