engineer

tim   .

                                                      


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.   hunkin

                                                         


cartoonist

 

THE MECHANISMS

 

Science museums all used to have displays of mechanisms similar to the ones in the clock. They were considered essential for training Ďmechanicsí and the models are obviously easier to understand than drawings. They disappeared because the rise of computers led to mechanical ingenuity being replaced with simpler mechanisms controlled by clever software. One of many examples is the sewing machine. These used to have elaborate mechanical cam systems to create fancy stitches, and now have computer controlled stepper motors instead.  

 

Even before the rise of computers, Iím not convinced the displays of mechanisms were ever that practical because always Ďthe devil is in the detailí. Some mechanisms only work on a small scale with tiny loads. Some need making really accurately. Some need really low friction bearings. Some transfer power ridiculously inefficiently. Some are only intellectual curiosities without any practical application. Choosing a mechanism for a particular application depends on so many factors the models donít show. Useful or not, they certainly are part of the history of teaching mechanics, and they are also just fun to watch and to play with.

 

ECCENTRIC

This is a useful alternative to a crank. Making an accurate crankshaft, like in an internal combustion engine, is difficult and takes time. A row of eccentrics is easier to make because they can have a single main shaft running through the middle.

 

CARDAN

This is usually used to convert linear motion into rotary. It was historically important on early steam engines.

SLIDING BLOCK

This is one of Paul Spoonerís mechanisms that he uses on his automata. Iíve never come across any industrial uses for it.

 

RATCHET

Ratchets are widely used, for example on winches and clocks. However I had never come across one in which the ratchet arm moves the wheel forward when it is rocking both clockwise or anticlockwise.

 

DAISYWHEEL GENEVA

A Geneva is a mechanism that converts a constant motion into intermittent motion. This one is sometimes used on electric clocks that advance the hands once a minute.

 

CURIOUS CAM

Paul found this in a book of ĎIngenious Mechanismsí. I suspect it was always more of an intellectual puzzle than for any practical application.

 

IRREGULAR CAM

Cams are widely used, for example for lifting the valves in internal combustion engines. Complex cams were also common in printing presses and industrial machinery. The cam follower needs to have low friction for a cam mechanism to transmit much power. 

 

LAZY TONGS

This is used in reverse on industrial riveting tools, a long easy pull creating a powerful short pull on the rivet. It is not an efficient mechanism as there are so many bearings.

 

BELLOWS

Low pressure air, as pushed out by the bellows, is used to power amazingly complicated mechanisms on player pianos. Paul also uses it on his automata. I had never tried it before but was amazed how much force it can exert.

 

LEVERS

This is a mechanism that used to be in Chicagoís science museum, copied from a photo online. I was curious to see it work, but donít know anything else about it.

 

QUICK RETURN CRANK

Both Paul and I use this mechanism sometimes to move automata characters. Itís easy to make.

 

TWIN COG

This can produce a bewildering array of different movements, by moving the position of the teeth of one gear relative to the teeth in the other. Iíve never come across any practical applications.

 

 



 

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