Monthly Archives: November 2012

Update On Longcase Clock

Completed cad designs of primary longcase movement this morning. Still need to add the driving weight and winding gear but the main gear train is now fitted together in the cad model. I found when I resized the gears from the original design that I needed to include an intermediate carrying plate in order to prevent the 2W gear from clashing with the arbor of the GW.

A clock is really just a series of gear boxes. Firstly comes the gear box for the second hand. This is more of just a direct drive. The pendulum interrupts a 30 tooth escape wheel. Because the pendulum swings in two directions from centre the escape wheel must be half the time increment So 30 teeth on the escape wheel for a pendulum just under a meter equals 60 seconds or 6 degrees for each step of the second hand.

Next comes the Cannon Pinion. This is not fixed to the main arbor but is able to rotate freely on it. You could in fact if you wanted have each of the hands on the clock separated in to an individual dial but of course we want to stack them up. This is achieved by making the arbor of each gear box in the series hollow so that its final driven gear may rest above the driven gear before it. Seconds. Minutes. Hours. This results in the arbor for the seconds being the first to emerge from the clock face. The minutes being next and the hour hands the next.

Where this now gets complicated is that the clock mechanism must be driven by something. It is a common misconception that the clock is driven by the movement of the pendulum. This is incorrect. A clock of this design is driven by a driving weight. What the pendulum does is to interrupt the progress of the escape wheel by the anchor that rests above it. This rotates back and forth in a carefully calculated arc that always interrupts and then releases the escape gear at each step.

Where this gets tricky is that you need a secondary gear stage to take some of the energy of the slowly lowering drive weight and to put that back in to the primary arbor to which the escape wheel is attached. The result of this is a highly effective regen system that keeps the pendulum going for much longer than it would if it was just allowed to free swing itself with no return.

Here are some pictures that break down the mechanism in the movement. The drive weight and its winding gear sit behind what is called the GW or great wheel. This sits on the lower centre arbor ( axle ) and is usually behind it.

At the very back of the mechanism behind the entire movement sits the pendulum. This will be driven by a small rod that pokes through a hole in the anchor. As the pendulum moves from side to side it moves a small rod in an almost transverse line relative to the anchor and extends through it. This provides the timing movement for the anchor.

I have not included the winding gear yet but this mechanism is a one way ratchet. In one direction it is caught up with the driving weight as it falls and pulls around the arbor of the great wheel. In the other direction it can be turned freely and returns the weight back to its initial drop height.

This mechanism is for a 30 hour clock which means it must be wound once a day. At the pinnacle of clock design a long case clock could have as many as 30 weights and run for an entire year without winding.

For My Friends

The world is filled with doubters. Tremulous and timid. Not even the margins of history have space for them. Always off the page they would remind us of how nothing can be done and how no idea is possible.

We must not listen to them. We must take risk and be as happy with success as we are with failure. Do not doubt yourself. This is the poison given to us from a wet nurse that must still cosset us in swath. Pathetic. Vile. I can share no common idea or opinion with such creatures anymore than I could with the dumbest insects. Even then this is to insult nature where many small and wonderful things may be seen toiling away driven as they are like so many little clocks against mighty odds.

If you commit yourself to a task do your best to complete it. Do not forgive the death of butterflies. These are small ideas that you are trying to give flight to that will be larger than you imagined.

Remember those people who doubted and make sure they are ignominiously trodden down under the heel of your achievement.

Your Future

Find no forgiveness or kindness for them. The world is made worse for them. You will go where they may not and see many incredible things.

Don’t even send them a postcard when you arrive for they are the worst of us and complete wankers!

Sometimes events will conspire against you. It is given that sometimes we are going to fail. We will fail in creating things. Sometimes a great work will be destroyed and you will need to start again. Sometimes the way ahead will not be clear. Great loss is going to happen. If the way was always clear then the task would be more easily addressed by some other. This is all a test of how much faith you have.

Stare down and DESTROY the filth that whispers defeat in your ears. Look it in the eyes and summon up all the anger that you can to eject it utterly from your person. Such people will not pick you up from the mud. They will not push you down when everything lights up. No you will look around and they will be quite gone. Still hiding in a trench somewhere crying.

I have no countenance for such people. No time. No respect. Just anger.

But then for those people who want to make things. Those who have small or little dreams or big and amazing dreams then I will dig in my boxes of bits and I will bring you whatever I have. Because you are my brothers and sisters and I believe that what you create will be pretty damn cool and I want to see if it works.

I will be generous with my time and I will encourage you. I will not be that pathetic off the page greyness that first resorts to difficulty and doubt and then falters.

Just ask… I am bound to have something that fits that axle somewhere … :)

John Harrison Clock



MALLFUNCTION! MALFUNCTION! MALFUNCTION . . . Generally grog is very well behaved when it comes to the spinning objects but I was polishing escape wheel and it has very fine teeth. Had good gloves on to. Caught up and the piece span in to my hand like I was trying to catch a freaking Shruikan. Opened up side of glove like a boss. Tore big chunk out of glove and blood and meat. Woukd have taken a chunk out of the bone I think without the glove. Oddly the escape wheel seems to have only got the mildest deflection from flat. Awsome,

On Gears


Most modern involute gears are cut using a hobb. The gear is rolled in the hobb against a hardened steel profile of its teeth.

But what did pre industrial age clock makers do. Apparently something called a Lancashire gear cutter which is a form of rotary mill.

A modern version exists called a Bergon. I found plans today for building a copy as the genuine article costs about eight thousand dollars!