First clock suggestions

[John HaineParticipant @johnhaine32865]

James, a 60 tooth wheel will be 48mm diameter at .6 mod and 64mm at .8 mod, the gears just get bigger, take more brass, look a bit large.

[roy entwistleParticipant @royentwistle24699]

James As john has pointed out it,s a matter of size 0.8 mod are usually ok for long case clocks

Roy

[AjohnwParticipant @ajohnw51620]

Some of the clocks that are about need several sizes of gear cutter. 0.8 mod was a jocular comment but I wouldn't be too concerned about the size of the clock or making cutters really. I happen to have a set of 0.8 mod for small gears and some 18dp cutters for larger ones. I have tools for making the cutters for the ME Myford gearbox but as I changed lathe it was an unfinished project.

Just thinking of economy really and feeling that 0,8mod would be a fairly common size for people to have who are into models.

John

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[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Ajohnw on 28/03/2016 17:01:34:

Just thinking of economy really and feeling that 0,8mod would be a fairly common size for people to have who are into models.

Unfortunately the gear cutters used for most models are not best suited for use as clock wheel cutters, having a different tooth form. Many clocks can be made with just one wheel cutter. Pinions need a range of cutters but you can make lantern pinions instead or buy ready cut pinions.

Russell.

[Sam StonesParticipant @samstones42903]

Here's where I get shouted down, but …

What's wrong with fly-cutters?

It's likely that the teeth of the escapement wheel will need to be cut that way.

Apart from the lantern pinions, that's how I cut all the gears for John Stevens skeleton clock, including the six-leafed pinion.

The teeth may not look pretty under magnification, and they certainly don't conform to any particular standard.

The `proof in the pudding' is that the clock has been running since 2011.

Regards to all,

Sam

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Sam Stones on 28/03/2016 21:31:08:

What's wrong with fly-cutters?

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Nothing

MichaelG.

[Sam StonesParticipant @samstones42903]

Thanks Michael.

That's the sort of support which gives me a warm feeling.

[Russell EberhardtParticipant @russelleberhardt48058]

That's interesting Sam. You can of course make fly cutters that produce a good approximation to the cycloidal tooth form but you have proved that it is not really necessary.

The cycloidal form minimises the friction but in a well made clock what is the biggest source of friction? I think it is a toss-up between the escapement and the friction in the pendulum suspension and air resistance.

Russell.

[Brian HParticipant @brianh50089]

Edited By Brian Hutchings on 29/03/2016 10:12:24

My first clock was John Wildings English Regulator clock. I intended making the case myself but I'm no woodworker so I contacted a cabinet maker in Cromford, Derbyshire who made one out of light oak.

Edited By Brian Hutchings on 29/03/2016 10:15:13

[AjohnwParticipant @ajohnw51620]

Posted by Michael Gilligan on 28/03/2016 21:35:00:

Posted by Sam Stones on 28/03/2016 21:31:08:

What's wrong with fly-cutters?

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Nothing

MichaelG.

I agree entirely Sam. Nothing and would expect to have to use them on some wheels. To be honest though I don't see why cycloid has to be used on clocks other than tradition. In some ways involute are easier to cut as pretty close approximation cutters can be made.

That looks to be a rather nice piece of work Sam – I should have added that initially rather than via an edit.

John

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Edited By Ajohnw on 29/03/2016 10:25:52

[Michael GilliganParticipant @michaelgilligan61133]

There is some very interesting reading on [and linked from] this page.

MichaelG.

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Edit: Just noticed that Ajohnw had posted the same link on another thread.

'Snap'

Edited By Michael Gilligan on 29/03/2016 16:45:39

[BazyleParticipant @bazyle]

Cycloidal gears as used for clocks have rolling contact so minimal friction but are not constandt velocity. This doesn't matter if the mechanism is going tic-toc. Involute gears for lathes and models have sliding contact so high friction unless well oiled but are constant velocity so your car doesn't go in a series of jerks.

The cycloidal form approximates to a straight line for larger diameters so you can get away with a simple form.

[Michael GilliganParticipant @michaelgilligan61133]

As an interesting aside … I would recommend having a look at this compartively new site about WorkClocks.

MichaelG.

[AjohnwParticipant @ajohnw51620]

Posted by Bazyle on 29/03/2016 17:27:53:

Cycloidal gears as used for clocks have rolling contact so minimal friction but are not constandt velocity. This doesn't matter if the mechanism is going tic-toc. Involute gears for lathes and models have sliding contact so high friction unless well oiled but are constant velocity so your car doesn't go in a series of jerks.

The cycloidal form approximates to a straight line for larger diameters so you can get away with a simple form.

That does seem to be conventional wisdom Bazyle but this shows the contact and force line on an involute

**LINK**

As I see it rolling not sliding contact.

However as with cycloids achieving a perfect tooth form is problematic when clearance and practicalities are included.

John

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[Sam StonesParticipant @samstones42903]

Thanks for your compliments John (Ajohnw) I’ll send you a PM later.

I’m not particularly proud of the results of my gear cutting, nor in fact the photograph which shows a mixture of old and new (clock parts).

As for gear-cutting, the teeth of the cannon and hour wheels in particular look like something from several centuries ago. At the scale I was working, the amount of curvature (involute/cycloid/radius) is hardly noticeable, and my simple radius should, and probably has been sufficient.

I think my next comments should be under a new/different thread, but I’ll leave them here for now. I anticipate some clever replies which I trust this old brain of mine will grasp.

Although I am supposed to know about gears and have a good head for geometry, I cannot get my head around the claim that cycloidal tooth profiles are purely rolling not sliding. If that is the case then why do gears wear out?

For any pair of teeth in motion (and while ignoring surface deformation), there are always two lines of contact travelling towards or away from each other. The momentary exception being as their relative direction becomes tangential /identical.

Although the geometry suggests rolling, surely there has to be some sliding?

What do the tests for gear-train friction tell us? Personally, I don’t have a clue.

Michael, I can’t bring myself to study your link, but it sure looks brilliant – **LINK**

Regards,

Sam (aka Dennis)

[John HaineParticipant @johnhaine32865]

**LINK**

Involute gears give rolling contact and can be hobbed to generate the profile exactly. Cycloidal gears are much harder to generate and it's also difficult to shape single tooth cutters, so just how close actual clock gears are to rolling contact is doubtful. The link above suggests, not very! Sinclair Harding, who make very fine clocks, use at least some involute gears.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 30/03/2016 07:54:43:

**LINK**

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John,

Yes, that ^^^ is an excellent page … I make no claim to priority, but it's the one that I was pointing Sam towards when I wrote earler:

[quote] There is some very interesting reading on [and linked from] this page. [/quote]

MichaelG.

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Sam (aka Denis) : you really should sit down quietly some time, and read it.

[jaCK HobsonParticipant @jackhobson50760]

I read 'the lost science … of harrison' by Laycock and came away with the conclusion that Harrisons prime concern for gear teeth was for the friction to be consistent in forward and reverse which allowed him to dismiss concern about recoil in the escapement design.

The book also shows in detail the problem with depthing errors, as suggested in the excellent linked page above, and further suggests that the usual depthng technique tends to introduce depthing errors (when driven forward, gears tend to feel better at slightly larger depth distance than therory).

I may have remembered that wrong.

[roy entwistleParticipant @royentwistle24699]

The biggest trouble with a clock train is that you have a large wheel driving a small pinion all through the train Apparently this is the least efficient and why friction has to be kept to a minimum

Roy

[John HaineParticipant @johnhaine32865]

Michael, it's on the same website but a different page! I found this link ages ago and it still works, though it isn't actually linked on the csparks site itself. This is an article by a guy very experienced in mass production of clockwork fuses on how cycloidal gears caused huge problems and why involute ones were much better.

(Actually just checked and it is linked right at the bottom of the page I think you pointed to.)

Edited By John Haine on 30/03/2016 09:22:23

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 30/03/2016 09:16:35:

Michael, it's on the same website but a different page!

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John,

This isn't worth debating, but … I wrote "[and linked from]"

… Which it is:

"Finally, I would like to mention a privately published monograph by my gear-expert friend, Richard Thoen."

MichaelG.

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Edit: inserted quote from web page.

Edited By Michael Gilligan on 30/03/2016 09:26:58

[Sam StonesParticipant @samstones42903]

OK Michael, But it had better be good!!!

Only joking and thanks for your persistence.

[John HaineParticipant @johnhaine32865]

Yes, sure, sorry!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Sam Stones on 30/03/2016 09:22:49:

OK Michael, But it had better be good!!!

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It is !!

John and I agree

MichaelG.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Brian Hutchings on 29/03/2016 10:11:28:My first clock was John Wildings English Regulator clock. I intended making the case myself but I'm no woodworker so I contacted a cabinet maker in Cromford, Derbyshire who made one out of light oak.

Nice looking clock Brian. I have recently completed the month going version and am in the process of making the case. Metalwork is much easier though!

Russell.

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