Don't slam on the brakes!

When we last visited our DUFA tall case I was expounding on the action of the hammers for chiming. In particular I find the elaborate metal shapes of the levers most compelling. A quick review of that last post will probably help the reader understand the material presented below.

A reminder that the two sets of hammers are bound to those two steel hammer arbors, each having an elbow-shaped lifting rod that are pushed up by their respective levers.

In this photo I've removed the arbor mechanism and we're looking at it from a different angle.

Certainly dirty but remarkably intact and with little wear.

Working from the left we have each arbor's pivot then, moving along the arbor, the lifting rod elbows, then a brass locking ring that is screwed down to the arbor and then a fascinating mesh of two metal pieces and then the big brass outer plate that the two arbors share.

It's those two meshing metal pieces, that I've never seen before, that have become something truly fascinating to your correspondent.

Here's a close up of me holding them after a light cleaning.

Those two pieces are effectively flat plates of metal with a hole in the center, like washers, that slip over the arbors and slide into place. But imagine those washers were stamped, cut and bent such that parts stick up, out and down in a very interesting pattern.

And now with the outer plate removed.

Now to the view below. The upper "washers" are fixed to the locking ring such that when the arbors turn, the upper washers turn with it. The lower washers lock to the outer plate via small locking holes in the plate. Those washers have little nibs sticking down that lock into the holes in the plate. You can see them in the photo above sticking downward. That locking has the effect that when the arbors turn, the lower washers stay put and don't rotate. The effect is one washer slides along, against the other.

So when that arbor above turns counterclockwise, the upper washer turns with it. Each upper washer has 3 nibs and each nib rides up along a matching sloped plate cut/bent into the lower washers as the arbor turns. 

As the nib rides up / against the lower washer's sloped plate it effectively pushes the washers apart, creating friction / separation pressure and this entire action works as a brake.

Amazing bit of engineering.

There is quite a bit of precision needed here. What these washer/brakes do is enable it such that the lifting rods will be raised by the lifting levers but then when the levers fall back, the rods won't slam into the levers. The brakes slow and stop the fall before the rods hit the lifting levers.

Alignment needs:

A. Adjust the hammers on their arbors so they strike the rods but then recoil back so as not to actually stay in touch with the rods ensuring the a note continues to chime and is not muffled by prolonged contact with the hammer.

AND

B. When the hammers fall ensure that they don't fall so far that they cause the lifting rods to hit the lifting levers. This is what the brakes are designed to do.

AND

C. The brake can't lock too tightly else it will create excess friction requiring extra energy to unlock the nib pressed against the opposite washer and slow or prevent the movement from raising the hammers for the next strike

AND 

There's even more things happening in the hammer strike that need adjustment that I haven't gotten to but I've made my overall point.

Perhaps it all needs to be seen in action to truly appreciate it.

The by dog the whole mechanism is ingenious.