Why is the 9 leaf clock pinion ommitted?

Hi Guys,

currently reading Malcolm Wild's book 'Wheel and Pinion theory' he correctly states Addenda constant for wheels and pinions but there is no mention of a 9 leaf pinion. I also find the same when looking on certain cutter websites.

There must be implications of using a 9 leaf pinion, I suspect something to do with the gearing ratio. Can anyone shed a light on this as ( leaf pinions are common in mass produced clocks?

Regards

Chris

In 65 years + I don't think I've ever come across a 9 leaf pinion

Edited By roy entwistle on 10/10/2020 13:02:51

Probably the fact that they do not appear in clock trains. Thornton's produce 6 7 8 10 12 and 16 as standard pinion cutters 7 being a prime and the rest having usefull common factors. It's the same as preferred values in resistors. You can make all the values and ratios you need from a fixed set of components.

Simply put you cant get them but you never need them.

regards Martin

Grimthorpe's A Treatise on Clocks points out that in clockwork wheels drive and pinions run. In this gearing up context he refers to a proof in Professor Willis's Principles of Mechanism that no pinion of less than 11 leaves can be driven entirely after the line of centres, ie they grind causing the amount of force needed to turn low number pinions to rise suddenly. The problem can be partly overcome by altering the shape of the teeth, but it's best to avoid pinions with less than 11 leaves. They can be made to work, but...

All based on reading - the only mechanical clocks I've made were Meccano, and their gears aren't ideal for that purpose. If a horologist says different, believe him!

Dave

Edited By SillyOldDuffer on 10/10/2020 13:24:21

Just for fun ... Have a look at #5 here: **LINK**

https://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_general;action=display;num=1437696305

MichaelG.

Hmmm...Mr Grimthorp hadn't seen one of the many clocks that have 64/8 and 60/8 ratios in their trains.

I don't think Lord Grimthorpe would have changed his opinion on small numbers of leaves on a pinion, he had very strong views on many subjects, rightly or wrongly. He was a very talented engineer, his double three legged gravity escapement is still regarded as one of the best for turret clocks. If he had a failing, it was probably of his uncompromising belief that his own opinion being always correct one.

His 'Treatise on Clocks, Watches and Bells" is available for download from the Project Gutenburg website and is worth reading, but remember to consider his opinions with caution.

Neil

Thanks for all posts Guys.

After extensive research I found the solution was simple. 9 leaf pinion parameters are specified in BS 978 table 3 but it is just that the cutter makers apparentrely choose to not cater for them but they do exist, I have a clock with one.

Regards

Chris

Edited By Chris TickTock on 10/10/2020 21:16:19