One of the projects that has been ticking over at the back of my mind is to build a clock. A quick internet search shows lots of ideas of building clock faces out of Lego, and some of these are very artistic. A lot of work goes into making some of these designs, and eventually my clock will have an arty face as well.
For the idea in hand, I am not content to use a purchased clock mechanism. The challenge is to build the mechanism as well. For this, Lego Technic is my weapon of choice, but there are a number of challenges:
- Lego axles are cross-shaped rather than round, and the gears have a cross-shaped hole in the middle so that the gears do not spin on the axle. The challenge is that a clock has two concentric axles for the hour and minute hand - three if you want a second-hand as well. So somewhere in the mechanism, at least one gear must be able to spin freely on the axle.
- It is considered extremely bad form among Adult Fans of Lego to deliberately damage one's Lego. Therefore the drilling-out of the axle-cross in a gear is not permitted. Having said that, I confess to doing exactly that a number of years ago.
- The minute hand rotates sixty times faster than the hour hand. A gear ratio of 60:1 is required between the two concentric axles. Lego gears are available with 8, 16, 24, and 40 teeth (there are a few others too). I leave the maths as an exercise for the reader.
On the front (in the lower part of the picture to the left) is a dark grey part , known as a "differential ". This part is found in many of the Technic vehicle sets, and your car has one too. I use it here, because it has round axle-holes. The dark grey bit itself is driven by the small 8-tooth gear to its right. The axle through the middle is driven from the back of the mechanism (top of the picture).
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If I have nothing else to do on Saturday after my lie-in, I might start work on the drive mechanism. Episode 2 of this saga will follow in a few months' time. If you can't wait for me to build mine, have a look at what others have done.