Cycloidal cutters

[Sub MandrelParticipant @submandrel]

[Sub MandrelParticipant @submandrel]

I've made a fair few involute gears using home made cutters. The world of cycloidal cutters seems very different – in John Wilding's series on the ME Jubilee Synchronome he advises the use of one cutter for gears from 16 to 0 teeth, including a crown wheel!

How does one decide the best cutter to use for a given size of clock gear and number of teeth, and is it possible to make acceptable home made cutters in a similar way to those for involute gears?

Neil

[John HaineParticipant @johnhaine32865]

There is a good book by j Malcolm wild, wheel & pinion cutting in horology, which describes all this.

[Russell EberhardtParticipant @russelleberhardt48058]

Thorntons who make cutters for clock gears sell six different cutters for pinions from 6 to 16 leaves but just one wheel cutter for all sizes of wheel. Theoretically each wheel will need a different cutter but not in practice.

I've not tried making my own cutters but the same principles apply as for involute gears. Some good advice is given here

Russell.

[Sub MandrelParticipant @submandrel]

Thanks,

That article doesn't make a whole lot of sense without any pictures though

There isn't a lot out there on designing and making these cutters…

Neil

[BazyleParticipant @bazyle]

The first hit on google seems pretty comprehensive

http://www.csparks.com/watchmaking/CycloidalGears/index.jhtml

Exactly how to design the tooth profile. Three cheers to Hugh Sparks for putting it out for the world to see.

[John HaineParticipant @johnhaine32865]

Read the article on Sparks’ website on why cycloidal teeth are obsolete though.

[John HaineParticipant @johnhaine32865]

Read the article on Sparks’ website on why cycloidal teeth are obsolete though.

[Sub MandrelParticipant @submandrel]

Thanks Bazyle – what did you google for? I looked for various things and didn't find that! And at the end of his pages he says "Sadly, I don't know of anything on-line about cycloidal gear design. If you make some gears, please make a web page and send me a note!"

John – Surely not obselete for clocks?

Neil

[John HaineParticipant @johnhaine32865]

Read the article! Written by a manufacturing engineer making clockwork fuses.

[John HaineParticipant @johnhaine32865]

The article I referred to is at

http://www.csparks.com/watchmaking/CycloidalGears/RichardThoen.xhtml

It is actually very hard if not impossible to make cycloidal gears exactly so they are always approximated by straight lines and circular arcs. I haven't seen any information on what errors this approximation introduces, I don't know if anything has been done. Involute gears however can be generated exactly using a hob. The article above suggests that actual production errors in cycloidal gears are quite large. The main reason usually given for using cycloidal gears in clocks is that they give lower friction in high-ratio step-up trains because their "action is before the line of centres". Thoen suggests that this is wrong, and that in practical production involute gears are (a) easier to make with smaller errors and (b) tolerate much larger errors (for example the wheels being too far apart) much better. I understand that one UK manufacturer of high grade clocks uses involute gearing. Of course, nowadays it doesn't really matter!

[Sub MandrelParticipant @submandrel]

This is interesting. I have read in several places that the errors introduced by using circular form tools to make involute cutters are less than the manufacturing tolerances for the cutters and far less than the errors at each end of a tooth size range.

Given that the main problem that seems to haunt all amateur clockmakers is depthing the wheels, going involute seems to be a no-brainer (as I'm not seeking either a gold medal or fellowship of the FBHI)

Neil

[BusterParticipant @buster]

Hi Neil, if you join my clockmaking group on yahoo you will see in the files section jigs for making your own wheel/pinion cutters http://groups.yahoo.com/group/Clockmaking/, also the davewestclocks web site has many of my published articles on clock repair/making, regards David

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

One of my college lecturers giving the Theory of Machines course had some very large Perspex gears segments – just a few teeth but accurately profiled . Watching the interaction of pairs of these gear segments at a size big enough to see what was going on was very instructive indeed .

He had examples of involute gears of different pressure angles and also cycloidal , lobal and conformal gears .

Apart from just seeing how the teeth interacted it was possible to see how the gear meshing action varied with depth of engagement errors .

Anyone that thinks a gear is a gear and they all work the same way would be astonished if they tried a similar experiment for themselves .

Two further things that the lecturer pointed out by a simple additional demonstration with a segment of a disk of Perspex were that in the local zone of contact of the various types of gear teeth they all had more or less the same curvature and that it was the local flank angle of the gear teeth that made the meshing gears different in action and more/less sensitive to depthing errors .

Further note :

Exact cycloidal gears or gear cutters can be generated using the actual properties of a cycloid – one planetary gear meshing a fixed gear and with the planetary gear carrying a cutter . However the arc approximation commonly used is so close to the ideal that it will serve for most practical purposes .

Michael Williams

 

Edited By MICHAEL WILLIAMS on 28/03/2012 11:37:50

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Buster on 28/03/2012 08:51:11:

Hi Neil, if you join my clockmaking group on yahoo you will see in the files section jigs for making your own wheel/pinion cutters http://groups.yahoo.com/group/Clockmaking/, also the davewestclocks web site has many of my published articles on clock repair/making, regards David

I can't see a file there on cutter making. Is it still there. What's it called. Or am I just going blind in my old age.

Many other useful files though.

Russell.

[johnp10Participant @johnp10]

Hello Gents.

A friend has acquired a Synchronome master clock and some slave clocks which he would to make into `stand alone` clocks.

Does anyone know of a suitable battery powered circuit which will provide the nessary 30 second impulses?

[Sub MandrelParticipant @submandrel]

Hello John,

A 32 KHz crytsal oscillator divided by 960,000 using a few logic chips than a buffer to make the pulse the right size would work, or a micro buff would use a microcontroller to do the job all in one chip,  a crystal, and a few capacitors.

A simple test circuit to prove the idea could be based on a 555 ic http://www.farnell.com/datasheets/80468.pdf don't expect a high level of accuracy, evin if it is called a 'precision' timer

Neil

Edited By Stub Mandrel on 28/03/2012 22:01:32

[johnp10Participant @johnp10]

Thank you Stub mandrel. I have passed on your information.

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