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Shortt–Synchronome clock No 11 Service


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For those that don't know the Shortt Free Pendulum clocks were made from the 1920s to the late 1950s and were the most accurate clocks made between the 1920s and 1940s.

Only 100 of these clocks were made and they were sent around the world to observatories and anywhere else that needed the most precise time keeping.

Very simply describing the clock it had a master unit that ran in a vacuum and a slave unit that synchronised to the master free pendulum unit and then could send timing signals to any number of other slave clock units.

The Perth Observatory which is now run by volunteers has 2 of these clocks Number 11 that was made in 1926 and after serving time at the Royal Observatory, Greeenwich to 1940, then it went to Edinburgh in 1941 for the duration of the war and then back to Greenwich in 1946 and then to Perth Obervatory in 1960.

The other clock Short clock that is at the Perth Observatory is number 94 which was ordered by the observatory in 1956 and delivered in 1957.

Besides these 2 clocks the observatory has a number of other significant clocks that they are wanting to get running after decades of static display.

The president of my association had been in talks with them for some time to service and repair these clocks and started doing so a few months back, but has only just in the last few weeks started working on the Shortt clock. It had been 'fiddled' with by people he didn't know what they were doing and besides being gummed up solid for reasons only known to the person that did it they had put paint over the ends of the friction plate on the centre wheel so it could no longer slip.

On boxing day he got the slave clock ticking after fabricating a new gathering wire and jewel and stripping and cleaning the whole movement, but it still needs some adjusting.

I went to visit him yesterday to have a look and bring my reference book 'Synchronome Masters of Electrical Timekeeping' by Brober Miles that was only just published to help him out with some of the items he was a bit lite on with information. Whilst I was there I took some photos which I thought may interest people.

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Dials of Slave Clock

Couple of the inside of the slave unit

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Apologies for this photo but I couldn't get a good picture with the sun shining through the window, but this is the vaccum chamber for the free pendulum

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Stand alone slave dial.

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I've got more photos and a slow mo video showing the pendulum being given its impulse but this is the limit I can upload to one post.

This is a very special rare clock, but once it is finished then number 94 will get the same treatment.

Number 11 is a type A model whilst 94 is the simpler type B model.

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This was the clock that was used before the 'atomic clock'.

The first atomic clock was built in 1949 but it was really only a proof of concept and didn't even reach quartz clock accuracy, the first accurate atomic clock was built in 1955 and the started to be sold in 1956, hence why the last Shortt clock was ordered in 1957 as after that date atmoic clocks were used.

Shortt clocks were the most accurate clock available from the 1920s to the mid 1950s

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I guess another way to  put it would be :

'This is the most accurate clock any of us could ever hope to work on'

As there are no mechanical clocks more accurate than this and you have to move to 'Atomic Clocks' to get more accurate and that requires a very different skill-set to work on.

The Shortt clock is accurate to less than a second a year if run in a temperature controlled environment.

Edited by Tmuir
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This is ultra cool. I have some much simpler master clocks with Hipp toggle escapments that I love, but these were for schools/factories etc. The Schortt is an animal all on its own. Amazing stuff. Last place I worked before moving overseas got in a couple of Riefler clocks from an observatory that were gorgeous but I left before work started. Vacuum chambers and all that, so cool.

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A couple more photos.

This first one shows the impulse mechanism.

Every swing of the pendulumdrops the gathhering pallet on the end of the gathering wire (Its just above the tooth in what would be the 3 position on the dial) onto the saw shape teeth and rotates the wheel and the hand. When the hand reaches 30 it realeases the impulse leaver (for want of a better word) which drops under gravity causing the impulse wheel to run down the slope on the impulse pallet giving the pendulum a little kit. If enough people are interested I will upload to Youtube a slow motion video of this.

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The next photo is the master movement that sits on top of the vacuum tube under a glass dome that runs the master movement. It has been cleaned and serviced but cant be installed yet as the impulse carriage which I don't have a photo of has a broken pivot on a wheel and that part was off at another watchmakers being repivotted. (Its a joint effort between 2 watchmakers to restore all of the observatories clocks).

The movement is sitting ontop of a basic wiring diagram for Shortt Clocks, which they hadn't been able to figure out why it did not match the clock they were working on, but my reference material solved that mystery as I managed to prove they were for clock number 94 (The other Shortt clock at the observatory) which is a Type B clock (simpler) than the Type A clock number 11 is.

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