Skeleton Clocks

Timekeeping is affected by variations in the strength of motive power.

As a spring runs down, the power available decreases.

The fusee is a grooved cylinder. with the cylinder reducing in diameter (I suspect that the curve is exponential).

There is a chain which wraps around the spring barrel as the spring runs down, and which pulls off from the fusee. The Fusee drives the clock.

When the spring is fully wound, the chain pulls off the smallest diameter of the fusee. When the spring is unwound, it pulls off the largest diameter of the fusee, with pro-rata between the two limits. The idea is that the torque (spring power X diameter) remains constant.

There is a parallel with the Derailleur gears on your bicycle in the ratio of diameter between the pedal sprocket and the wheel sprocket, where there is an attempt to keep the torque (required rather than delivered) constant.

Model Engineer in 1972 vol 138 issue 3434 had an article on Skeleton clocks running for 5 installments

Then in 1983 vol 151 and onwards there was an article on a Grasshopper Skeleton clock that ran to 25 parts plus two extra in 1987

-- Regards,

John Stevenson Nottingham, England.

Thanks John and Airy for your replies.

I have all the 1972 volume and am considering this. I have the first 3 of the 1983 volume (I appear to be missing all of vol 152). I have shown 'er indoors and she doesn't like the later one anyway, so it looks like the earlier one.

Having looked through the mags, the main frame is made from BMS. Whilst I could do it with this, is there any harm me making it from copper or brass? (I am considering the use of a mixture of materials to get nice contrast.)

Also, in order to stopping the finished item tarnishing (forever polishing) what would anyone suggest?

Thanks. Dave. ~~ Customise your internet experience

I believe John Wilding has written books for the construction of such clocks. Look at his web site

A fusee is a device designed to even out the torque of the mainspring as it unwinds. The spring is enclosed in a drum (known as a barrel) which is connected to the fusee by a line or chain. The fusee is approximately conical and has a groove cut into it to locate the chain/line. It also has a gear (known as the great wheel) which connects to the rest of the train. A fully wound spring has a high torque initially so the line operates on the smallest diameter of the fusee, as the spring unwinds so its torque decreases and the line operates on increasingly larger diameters of the fusee. The slope of the fusee needs to be matched to the spring characteristics to obtain a reasonably constant torque.

Cliff Coggin Kent UK

The message from "Dave" contains these words:

Dave. John Wilding has a good book "The Construction of a crystal wheel skeleton clock". His books are very informative and easy to follow. Bill Lamond

Although quite expensive at £30 for a pile of photostatted sheets held in by an office-style plastic edge binder.

Dave,

A brass "frame" is fine and more traditional (as well as being IMO more attractive). I haven't seen the designs referenced here but I suspect that BMS may have been used to keep the cost down. Skeleton clock frames were usually made from brass (sometimes cast) and were typically around 4 to 8 mm thick dependant upon the overall size of the clock. The frames need to be thick if it is going to be a fusee movement as the springs required are relatively large and powerful, and being 'skeletonised' there are a number of weak points built in when compared with a non-skeletonised movement. Odd as it may seem, brass plates do not need bushing (until they have been running for 50 years or so).

I have never seen clock made in copper, I suspect it may be too soft and too expensive.

Brass skeleton clock frames are often lacquered to keep the tarnish at bay although, in my experience, if a clock is covered by a reasonably well sealed dome or case, they only need repolishing every 5 years or so. Mostly, unless ball races are used, the clock needs to be thoroughly serviced (and therefore stripped down) every 5 years anyway, so it's not a big deal if you don't lacquer it. If you do lacquer it, make sure the lacquer is removed from the pivot holes.

If you're not already 'geared up' to build clocks, the things to consider are:

a) How are you going to make the fusee? - If you have a CNC lathe or 4-axis CNC'd mill then life is good, otherwise you will need to make or buy a fusee cutter for the lathe (they are available to buy but they're quite pricey).

b) Does the design you're using require many gear cutters? Remember that wheels and pinions need different cutters and each different module size needs a different cutter - cutters can also be pricey. Single point cutters are fairly easy to make but are no good for pinions. Lantern pinions may be the answer in these circumstances. Multi-toothed cutters are a nightmare to make and are seldom worth it for 'one-offs'.

c) You will need a depthing tool, again, they are expensive to buy although some designs are reasonably easy to make.

I hope it helps. I have designed and built a number of clocks (including skeletons) in the past, so if I can be of any help, feel free to ask any questions.

Regards

Mark

Somebody must make fusee cutters in the first place, and surely it is one of the strengths of we model engineers that we can turn our hands to making anything?

18 Feb 72 Model Engineer has an article on a tool to cut the groove, once the fusee shape (exponential?) has been cut.

The article is reproduced in Chapter 29 of "Tools for the Clockmaker & Repairer", one of those John Wilding books that are photostatted and edge bound. (OK - I admit to buying a couple of them!)

For a good general intro to clocks and watches, Adam Harris at camdenmin.co.uk is publishing a facsimile of the 1914 edition of Britten's "Watch and Clockmaker's Handbook Dictionary and Guide".

There is an Alan Timmins design for a skeleton clock in volume 3 of EIM (1981). is this any good for you. *somewhere* i will have these issues if you need a photocopy.

regards

Bob

Can you throw some light on something that has bugged me in the past?

I recall reading the that the 'best' fusees- ie those the most accurate clocks- had a curved slope, a "wasted parabola" was the description, as I recall. Did the early clock makers have the knowledge, facilities, and consistent quality materials (esp the spring) to determine the shape mathematically or was it all trial and error?

I believe the slope was determined empirically i.e. almost trial-and-error. Even if the slope of the fusee was not well matched to the spring, there would still be a dramatic levelling of the output torque compared to a spring without a fusee.

Cliff.

trial-and-error.

That makes sense. Thanks.

The message from "Dave" contains these words:

Dave If you are thinking of getting any of John Wildings books, which I would heartily recommend, try giving the BHI a ring. British Horological Institute. Upton Hall, Upton, Newark, Notts. UK. NG23 5TE Telephone (01636) 813795 They used to stock them, and recently they were selling them at a reduced rate. At any rate they are, in my opinion, well worth while for amateur clock makers like me.

Brian,

I have just had a look in Britten's, and we get the following ..... "To determine the shape of the fusee is much more complicated and requires first of all that the mainspring output curve is determined."

I note also that there is an entry for 'Fusee Engine'. Here we read ..... "A form of screw cutting or threading machine for forming the grooves in fusees; the shape of the fusee can be controlled by a guide plate which has to be changed for each different fusee."

The Fusee was invented c.1450, perhaps earlier - it says.

Thinking about it, I suppose that when the spring is fully unwound the fusee is of infinite diameter! :)

Mike

I don't agree with you. There's a lot of nonsense and silly taboo in this country on an event that we shall all experience. There have been

300,000 further deaths throughout the world since the time of that discussion, deaths which have not stirred a tear in anyone's (from this NG) eye. Does anyone hear feel guilty that they did not shed a tear for each and every one of those 300,000 corpses or their near relatives?

No, they didn't.

By the same token I did not shed a tear not experience any emotional reaction from the OP and I said so, and dissociated myself from the OP.

Perhaps there are those reading this Ng who dislike truth, or who dislike truth about themselves?

This matter has its genesis in a discussion a few months ago about driving stepper motors direct from PC's. I had some commercial experience of this and so I shared it in all sincerity with the NG.

John Stevenson did not understand the technical issues involved and resorted to a series of rather silly and infantile outbursts, getting more and more offensive with each of his postings. Every one of those postings of his was out of place in a public discussion forum.

I criticised him for the anti-social way in which he was posting to a public discussion forum, but I did not realise that he was the leader of a gang of escapees from the school playground. They all rounded on me and have continued to do so ever since, on the slightest pretence.

My position in this NG has always been a technical stance, and a stance for civilised and mature behaviour. I criticised a number of people for their infantile and silly posts, and I stand by that criticism.

I can thoroughly recommend that book, as the name suggests, it is in dictionary form but it covers a phenomenal range of horological subjects, some are maybe outdated now with our modern machinery and materials but will give you a pretty thorough knowledge base. It's a 'must have'.

There is also what is probably a companion to it, again by Britten, called "Horological Hints and Helps" which is also very helpful.

Mark

To quote your 'words' Airy, "Bwahahahahaha...............................hahahaha!!!!!!" ...(_!_)...