Alignment. Who knew?

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Our DUFA has recovered from surgery however your local horologist knew that sewing the patient back up would not be child's play.

As previously mentioned, our German friend is a "rack and snail" movement. Often reassembling a movement is just getting all the wheels and bits in the right holes and such. With a rack and snail there are very specific alignments needed for wheels, pins on wheels and levers so that clock will run correctly. 

I cleaned and reassembled a Vienna regulator last year (for another blog post). I did not get the rack and snail correctly aligned. The clock won't strike the hour. At all. Time runs beautifully. It's one of my best clocks. I have not gone back to its rack and snail yet for fear I'd botch it (or worse) and decided to learn about rack and snail on our German friend instead.

And learn I have.

Here's an example. See this wheel? It has a "pin" sticking out of the edge of the wheel.


Here's one with several pins.


Those pins must be aligned precisely to matching levers during the reassembly. Here's a photo of a lever's arm correctly abutting a pin (prior to my disassembly).


Does that pin look a little bent to you? It did to me.


Fixed that.

Now that wheel with multiple pins? It's used for striking the hour. As the wheel turns, the pins lift a lever that turns a rod that raises a hammer that strikes a gong.

Whew.

Here's that wheel with a pin up against the lever.


A close up


OK this is pretty much how I reassembled the movement. 

Well turns out that was wrong!

The clock would strike one less than the time. 8 strikes for 9am, 4 strikes for 5pm, etc.

What!?

Lot's of research on the NAWCC boards and I discover that when the movement is reassembled and at rest that specific lever must sit in the space BETWEEN two pins of that wheel, not resting against a pin.

OK apart it comes again. Getting these wheels exactly aligned is challenging.

Here's another example.

I fixed the lever problem above, reassembled the movement and hey presto it strikes correctly! 9 strikes for 9am, 5 strikes for 5pm, etc.

Except at noon. 

When it only strikes 7 times. What!?

Seven?

All the other striking is fine. 3 at 3. 11 at 11. Etc.

Huh?

Ahem. 

Turns out when you reinstall a snail and have the mesh with the second wheel off by one, yes one, tooth, then the rack hammer won't fall correctly against the snail when it strikes 12.

At 12pm or 12am, the rack hammer will fall and the snail is one tooth too far clockwise causing the hammer to hit the edge of the snail wall instead of flat against the base of the snail. As seen below.

What I did. There's the hammer stuck against the wall of the snail.

Nope

What was required. Re-meshing the wheels by one tooth allowed the hammer to fall all the way to the base of the wheel and strike normally. Thank dog for the NAWCC gang as, it turns out, I'm not the first person to screw this up.

Yup

AND NOW A SPECIAL EXTRA GUEST STAR!!!

My first video on the blog!

Here's a video of that striking pin wheel in action. The strike wheel (multiple pins) turning, each pin lifting the lever, which turns the rod and raises and then releases the hammers. I took this in the middle of trying to figure out why my first reassembly resulted in incomplete striking. If you watch right at the end of the video you will see the striking complete and the rod is sitting on a pin on the wheel (around 14 secs in). That's what was incorrectly aligned during my first reassembly. Click on full screen. It's a large video image.



Suffice it to say I now have a pretty decent grasp of how rack and snail striking movements work and how to align them correctly. 

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