First clock suggestions

I have a kit of parts for a John Wilding eight-day weight driven wall clock (with instructions) that I will never get round to making. PM me if you are interested.

Brian

I couldn't find a photo of one of those. Maybe it's my browser but without a shot of the completed clock who would buy it? Or maybe they are one and the same.

I've looked around at skeleton clocks at times hoping to find some plans as I don't really want the instructions to go with them. Also one that only uses 0.8 mod for the gearing.

John

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I might respectfully suggest that 0.8 mod maybe rather large for a skeleton clock I would expect something like 0.6 mod

Roy

John,

This is a link to a picture of the completed clock, on the second site link that I sent **LINK**

Roy,

I am happy to show my ignorance: why would a 0.6 be better than 0.8? Is it a metter of cosmetics?

Regards,

James.

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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.

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

Roy

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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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.

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

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Nothing

MichaelG.

Thanks Michael.

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

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.

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

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

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

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.

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

MichaelG.

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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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)

**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.