Monday, 28 October 2013
The generosity of Thomas Wall - now famous in the UK for making sausages, pies and ice cream led to the setting up of the Thomas Wall trust. I took this photo in Sutton of the Thomas Wall Centre clock.
Sunday, 20 October 2013
Decimal or "French Revolution Time", introduced in France in 1793 during the French Revolution (it didn't catch on though) - each day was 10 hours long, each hour 100 minutes, and each minute 100 seconds.
Folkestone is a coastal town, and looking across the English channel on a clear day you can see France. The clock in the photo is one of 10 decimal clocks in the town; they are part of an art commission to show the close ties between Folkestone and France.
Thursday, 20 June 2013
By Stuart Ward - June 2013
Here is a description of modifications made to a Meccano No.2 Clock Kit to improve reliability and achieve a useful 24-hour run time.
The original kit was difficult to get working properly, had a huge driving weight and only ran for a few hours unless fitted at the top of a stair well with a very long string!
Photo 2 shows the timing weight sprocket drive. The sprocket is small to reduce the travel of the weight. The sprocket is free to rotate on the shaft. Screws and locknuts in the grubscrew holes act as pegs to engage on the spring-loaded flap on the large gear. During winding the pegs push the flap open. When the weight is applied the flap rests against the long stop bolt and the peg rests against the flap, thus providing the drive.
The use of small sprockets for the drive chain requires the friction to be minimised. The biggest cause of friction is in the pendulum bearing. I made a pair of brass pin bearings as shown in photo 3. Some form of rocker mechanism may work even better. A lot of time was spent working the friction out of the timing gear train. Every bearing has to run totally freely, and all were lubricated. The centre shaft which carries the weight is a bad area. It has three bearings and it is very difficult to get all three perfectly aligned. I cheated and reamed the middle hole out a little! I also greased it to stop it binding. The heavily-loaded gears at the weight end of the gear train were greased. The faster-moving gears at the pendulum end were oiled.
The same system is used for the chime sprocket drive shown in photo 4. Springs are all sorts out of my odd springs bin. The heads of the peg screws needed to be filed to miss the chain.
The sprocket and gear arrangement on the chime ring is very clever but troublesome. A common problem with the Meccano sprocket chain is that it binds up on the sprockets after a couple of revolutions. This is due to a slight pitch mis-match between the chain and the sprockets. It can be solved by firmly pinching the chain together between the sprockets in a couple of different places. This stretches the chain slightly and hey-presto- the binding disappears!
The speed of striking is governed by an air damper. The air damper runs at high speed. When the strking stops the mechanism has to suddenly stop the spinning air damper, which loads the stop lugs on the chime ring heavily. This has been prevented by a Meccano ratchet and pawl as shown in photo 5. The large gear carrying the pawl is free to rotate on the shaft and is driven by the ratchet gear. When the ratchet gear stops the large gear and air damper run down to a stop without back-driving the gear train.
Photo 6 shows the rearranged striker release mechanism. The lugs on the chime ring present a high force on the stop arms when the striker stops. Meccano supplied special extra-strong black-painted brackets for the chime ring lugs to stop them bending. As the clock ran the stop arms were driven inwards into further engagement by the cams on the timing gear. This required considerable force- enough to stop the clock!
I’ve used cranked axles for the stop arms and put them the other side of the cams so that they normally sit in engagement. When the time approaches the hour the cam pin now pulls the stop arm out of engagement, releasing the chime ring and starting the striker. This requires much less force.
The stop arms are held in the up engaged position by Meccano tension springs, and the ends of the arms are guided by a pair of fishplates bracketed off the frame. The stops are made from cranks extended by 135° brackets and reinforced by three-hole strips. Photo 7 shows the stops and guides. The modifications took some time but now the clock is more than just a novelty- it actually forms a useful working timepiece that is wound daily and runs constantly in my office, and it actually keeps good time too!
Note from Alan: Many thanks to Stuart for this article. This article is Stuart's response to the blog post Meccano Clock Kit 2 in January 2009.
Saturday, 25 February 2012
It's 153 days until the opening ceremony of the London 2012 Olympic games!
The countdown clock is in Trafalgar Square, London. The clock was created by Omega who are the official timekeeper of the games. One side of the clock shows the time until the opening ceremony of Olympic Games and the other side shows the time until the opening ceremony of the Paralympic Games.