Duncans Metal Pages
Prime numbers
Last updated: 13 Nov 2018


Prime numbers

Prime numbers are those which can only be divided by themselves and 1.  If you are wondering what the relevance of this is to cutting gears, you will find out when you need to cut a gear with a prime number of teeth. ;-)

The only way to cut a gear with a prime number of teeth using a dividing chain, is to have a gear in the dividing chain which is that number, or a multiple thereof.  Prime numbers up to 127 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127.

There are neat ways round this, like using a differential mechanism to add and subtract different ratios to get primes.

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