Closing the chapter on meshing

First it is important to acknowledge that the coefficient of friction for approach action cannot be different from that for recess action, for when Leonardo da Vinci slid weights across a table, observing that "Friction produces double the amount of effort if the weight be doubled," he didn't have to differentiate between pushing (approach) and pulling (recess)

That is true for free moving sliding weights. However if the resultant of the frictive vector and the normal force vector acting on a pinion is such direction as to pass behind the centre of rotation it will act to increase the normal force vector which increases the frictive force vector in consequence hence the wedging action.

Personally I would always use cycloidal on small clocks if only for the look of the wheels. Tower clock are different animals and for them involute wins hands down if only because you get a stronger tooth.

regards Martin

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Oops

... well, at least it saved me worrying about whether to write Davis’ or Davis’s

• Wilfred Owen Davis, Engineer, Research Department, Aviation Division, S. Smith & Sons (England) Ltd.

MichaelG.

With no intentions of appearing gender biased, I was brought to my senses by what appears to be a sign of the times when MS Word underlined in blue my use of the word ‘gentlemen’.

So I tried gentle men, and guess what, MS Word responded with the instruction to use ‘gentlemen’!

And all I wanted to say was ‘Gentlemen, Thank you for your interest and contributions!’

Sam

Any tin hats to spare?

Neil wrote … Pah, Sam, it works which is what counts

Thanks Neil, and well spotted.

Had I been more observant before cutting my own clock teeth, I could have taken the easier route of a radiused cycloidal addenda. Instead, mine were a botched up involute, a recollection from night school perhaps.

I’m sure too, you know better than I that, as with ordinary wheels (which were originally square until the corners wore off), most of the Antikythera gear teeth appear to be triangular and nothing like cycloidal. At least that’s how Chris of Clickspring has cut his Antikythera teeth.

**LINK**

Martin, Thanks for the prompting re force vectors. I couldn’t think of how to apply the potential variance between entry and exit friction. Maybe I’ll fire up the laptop and ponder some more.

Sam