Bridges & Gears

Now that all the gears, cams and levers are worked out for the perpetual calendar mechanism, I was able to design the bridges that hold the arbors all those parts pivot on.

With previous perpetual clocks I didn’t need to design bridges, because the two plates behind the mechanism would hold all of the arbors, and the parts were cantilevered out front. But with this piece the giant wheel of moons spins where those arbors would need to be. So the arbor for each part is between the front plate, and a bridge, which is essentially a mini plate just for that part.

The other thing I worked on is the gear-spokes for the 2nd and center gear. I was already pretty happy with the way the design of the bridges came out, but I stumbled onto something with the gear design that has me pretty excited.

I drew a few designs at first. Some of them looked like the spokes from “Perpetual No.1”, in which there are small recessed panels that mirror the number frames of the clock face. The other designs looked more like the gears from “The Grasmere Commission” or “Twisted Twelve”. Either direction would have been really good. But then I had the thought to not just pull from design motifs in the clock, but mirror the clock itself in the gear spokes.

The result is what I hope will be my favorite gears yet. The drawings are still on the loose side, but this direction is definitely something new, and something I’m excited about.

Mechanism design

This week I sat down with a pencil to figure out all these tangled mechanisms.

Yes…a pencil. That’s my big fancy tool. Creating these mechanisms is, above all, a design process for me. No CAD or solidworks. Just lots of drawing, re-drawing, and refining. I use the light table and a protractor to look at the levers in different positions of their amplitude. This is to not only check that they don’t run into each other, but also look at the shapes to see how they visually interact. It’s a sort of back and forth balancing act that hopefully leads to a mechanism where all the shapes and angles look good and flow together, no matter what position everything is in. 

The drawings piled on this disaster of a work surface include:

-The lever that works off a cam on the hour-hand, clicking a 24 tooth ratchet once an hour. Almost everything works off the rotation of that 24 tooth wheel, so things are very mechanically busy in that area.

-The great lever. This controls the calendar hands, telling them how many days to jump forward. Also attached to this lever is an arm with gear teeth on the end of it, which moves the gear train of a drag-fan that slows and softens the action of the mechanism.

-The day click. This simply bumps the hand for the day of the week forward one click with each rev of the 24 tooth wheel

-The moon-gears. Of all the drawings this one looks the simplest, but it’s actually kind of interesting and unique (for me) to this clock. In order to make the moon as big as it is, I had to make the moons span the entire mechanism. The four moons will rotate inside of a giant gear that spins around the center axis behind the whole perpetual-calendar dial. Those gears work off of the 24 T ratchet, reaching out and down through the front plate to engage with the big moon gear.

I’m admittedly not very good at explaining this stuff with type. It’ll be easier once it’s made and I can show pictures or video.

Next I have a few small clicks and stops to design, and then I have to design the bridges that hold all of these mechanisms in place.

The great-lever & drag-fan arm.

The day-click.

The lever & click that advances the 24 tooth ratchet wheel.

The moon-gears

The Beginning

Not long after the start of the new year I got to work finalizing the design and drawings for my newest endeavor. A six-foot-wide wall-hung clock, complete with a perpetual triple-date mechanism and a shadow moon-phase display.

The word “perpetual” means that it will keep track of the date and automatically account for the number of days in each month, including leap year. The term “triple-date” is because it displays the day, date, and month. And “shadow-moon”…well, I’m not sure that’s even the technical horological term, but I’m calling it that because rather than the moon moving through a window to show the phase, the moon stays stationary, and a shadow will move in front of it to show the phase.

Fun fact, normally the shadow would travel counter-clockwise, because that’s how the shadow appears to move across the moon if you’re viewing it from the northern hemisphere. However this clock is for a client in Perth Australia, and they actually see the shadow move in the opposite direction. So for that reason I’ll be reversing the gearing so that the shadow moves clockwise across the face of the moon.

One thing of note, mechanically speaking. The placement of the moon is particularly challenging. The shadow will need to sweep through an area that normally has all of the arbors for the cantilevered perpetual mechanism. There’s also a set of gears for the drag-fan of the great lever that usually go where the shadow now has to be. There will be some bridges, unique looking gears, and general mechanical gymnastics necessary to pull of this display.

Good thing I like a challenge. This piece will be well worth the extra work!

Here are is the drawing for the new project. There are two versions - One with hands and one without. I always draw the final without hands so I can clearly see everything that needs to be cut out.

All of the progress for this piece will be posted here. More sparsely at first, since I’m still handling the filming and shipping of my last project. Eventually posts will be once a week.

Hope you’ll follow along.

Thank you & enjoy the creation of “PERTH” !!!