My skeleton clock

This may be an opportune time to follow up on all my previous (clock) postings, having been delayed due to several health issues.

With the help of a very kind friend who sent me a couple of helical balance springs to try, I was able to set my `John Stevens’ clock ticking under power. It's only been abobut 35 years in the making!?

The once-on-the-hour bell is quite distinct and puts a smile on my good wife’s face whenever it rings. It was necessary to `invent’ an additional spring which would `catch’ the bell hammer and stop it from yammering several times when it struck the bell.

There is one snag however.

The clock ticks (beats) too fast, taking only 28 minutes between bell tinkles, and for the minute hand to traverse one hour of the chapter ring. Upon closer inspection of the balance spring I found that the spring wire is about 37% larger in diameter. In terms of wire stiffness, this is a whopping 4 times greater (diameter raised to the fourth power) than my previous calculations. So I made yet another trip to see my friend with a music shop, and bought some more guitar strings. I have mentioned in other threads that, in abandoning a flat section spring for a round wire, I calculated that I needed a wire diameter of 0.2mm (0.008"). It just so happens that this is the smallest diameter of guitar strings. Lucky me!

So now it’s back into the garage to try a couple of new spring-winding ideas. Despite lots of help from ME contributors, my previous attempts at winding 0.2mm diameter wire around a 4mm mandrel by hand, have been thwarted by several issues. None the least being varying helical pitch.

I have also been warned several times that making a helical balance spring is one of the hardest tasks in clock making and repairing. But failure at this point means that the clock would be almost useless. Perhaps I should have started with making the spring, or gone the easier way and used a pendulum, with a falling weight for the power. No, not for me!!!

Thanks for your response ADY,

 

If you like that kind of history, which I certainly do, I would indeed recommend reading "The Illustrated Longitude" by Dava Sobel. If I remember correctly, it was also made into a documentary for TV.

 

For reference to my previous threads, please insert as appropriate - the words `Balance' or `Spring' or `HobbyMat' into the `Keywords' column.

 

As mentioned in one or other of these previous threads, the lathe I’m using (a HobbyMat with a constant mesh leadscrew) is not very friendly in the screw-cutting or spring winding department. I shall therefore continue winding the chuck by hand, with a couple of changes noted below.

Before I do, I must reiterate warnings (especially those of other ME readers) about the dangers of winding springs on a lathe.

DO NOT DO IT UNDER POWER!

To reduce the risk of an accident, turn off the power supply to the machine.

Addressing my current issue of variable helical pitch, I note some of my previous efforts as follows :-

For strength purposes, I made sure that there was a nicely polished fillet radius at the corner of the mandrel where it steps down from 6.4mm (1/4") to the 4mm working diameter. Working in the plastics industry for about 50 plus years, has made me particularly conscious of failures due to sharp corners and consequential notch sensitivity.

Inadvertently, with the anchor hole for the wire drilled through at the 6.4mm diameter, (again for strength, but more especially to limit deflection), I have probably allowed the wire to slide and roll over the fillet radius down to the 4mm diameter, introducing an unwanted twist to the wire. I used gravity to tension the wire which required a feed/guide pulley some 200mm from the tool post. I'm unsure if the wire should be fully controlled as it wraps around the mandrel or if it should be free. With very limited workshop (garage) facilities, there is very little I can do to set up the best method.

What I propose to do is drill another wire anchor-hole through the 4mm section so that the wire only makes contact with the mandrel at this smaller diameter. Using a length of timber placed horizontally and fastened to the lathe tool post, I will move the feed/guide pulley so as to extend the free length of the wire to its maximum of 1 metre.

 

It was a surprise to find that the guitar string (made in America), was 1 metre long.

 

They may get to complete metrication eventually, says he tongue in cheek.

 

Best regards,

 

Sam

Edited By Sam Stones on 15/05/2011 00:57:35

Edited By Sam Stones on 15/05/2011 00:59:20

Edited By ady on 15/05/2011 01:27:38

Edited By ady on 15/05/2011 01:31:06

Edited By ady on 15/05/2011 01:40:47

Edited By Sam Stones on 15/05/2011 02:45:26

Edited By ady on 15/05/2011 03:34:37

The bl . . y thing was plated steel. After all these years you would think that I’d know better.

Faced with a limited range of tools, I pondered about the simplest way to form the (4.9mm x 4.9mm) square hole in the key which matches the square end of the fusee arbor. So, at the end of the key shaft I have sawn and filed a shape which forms two opposite sides of the square hole.

A couple of flat bits of brass will be silver soldered to close off the hole, and I expect the fit on the arbor will be quite neat.

I’ve also pondered whether to reinforce this end of the key shaft with a steel ferule, thus increasing the key’s (burst) strength. Despite the clock having a maintaining mechanism, I have visions that if the key were to break mid-wind, the clock could suffer damage too. The resultant (ferule) diameter needs to be quite slim to sensibly match the rest of the clock, and would best be a press fit over the brass. Alternatively, I’m tempted to use Araldite.

After getting the balance spring right, the last test will be making a case, for which I have had heaps of helpful suggestions. Although appearing to be lesser challenging than other aspects of the clock, the case has to satisfy several functions, non-the-least being dust exclusion while allowing it to `breath’ during the wide temperature fluctuations. Australia can become quite warm during the day, while getting pretty cool at night. There can also be an `impressive’ show when it comes to dust.

Regards to all,

Sam

Thanks for your response Terry, I hope you won't mind, but I’ll address your ideas in a moment.

First, I have to say that last night while watching TV, the clock was ticking away merrily in the background albeit at twice its intended speed. From the vicinity of the clock, there was a sudden `clatter’. Actually, clatter is a bit too strong a word because the noise was that of a pin dropping. There was a noticeable change of clock beat too, although it was still running but at a slower rate.

When I investigated, the clock was ticking but with less obvious vigour by way of the balance wheel and escapement. Peering closer, I could see that the taper pin (actually a piece of sewing needle) was missing from the bottom of the spring. This pin is 0.82mm diameter, has a flat along one side, and is wedged into the balance spring collet to attach the spring to the balance wheel arbor. Here's the collet.

The split collet is a friction grip on the balance wheel arbor, while the smaller hole accepts the bottom end of the balance spring, and the 0.82mm pin (sewing needle).

Although the clock was still ticking, it was clear that being loose, the spring could not offer the same stiffness, and was perhaps rubbing against itself or slopping around in the collet hole. Some of this terminology can be reinterpreted, but I won’t go down that path. As expected, the clock eventually stopped, but the experience gave me additional confidence that the escapement was not as tight as it once was. Previously, I had needed to relieve each mating bit of the escapement to ensure `freedom without shake’, as the books tell us.

Here's the lever escapement. The 0.75mm pin in this picture is the guard pin, not the 0.82mm pin which grips the spring wire in the collet which would normally appear on the 1.5mm diameter arbor (ie. the main `shaft' running top to bottom in this view).

Upon reflection, it is clear that the pin doesn’t fit properly because I made it for a spring with 0.2mm diameter wire, not 0.28mm as per the spring sent to me by a very helpful ME gentleman who knows who I’m talking about.

Terry, I really appreciate your comments, as I do for the many others who have contributed to my threads. I think too, that you’ve revealed another couple of issues about spring winding. I must, however reiterate that I’m using a borrowed Hobbymat lathe, and presume that it will run at about 250rpm as suggested by ADY. So, while back-gear would be handy, I have to stick with hand winding. What you have done is draw my attention to (close-coil) winding a just sufficient length of wire onto the mandrel to make one complete spring. I’ve been using up most of the 1 metre length of guitar string in the hope of achieving a useable length of spring. The hardest part has been controlling the spring once it has been cut free. Previous attempts have resulted in coils flying everywhere, including wrapping themselves around each other. With the wire being so fine 0.2mm (0.008"), the task is really tricky.

The ends of the spring are finished differently to those you describe, and don’t need to be ground flat. The top end of the spring curls inwards slightly to engage with the balance spring stud (cock). The bottom end curls inwards to within 1.2mm of the balance wheel arbor.

Phew!

Edited By Sam Stones on 18/05/2011 04:56:20

Edited By Sam Stones on 18/05/2011 05:00:20

Hi John,

Thanks for your post. I can say that I haven’t given making a handle much thought, probably due to the fact that having disposed of my workshop, I’m limited with having suitable materials to hand, and the lathe is not my machine. Also, as you indicate, the handle would not get used too often. A bit of laziness would also enter into it.

I should give it more thought, because it’s not easy pushing the small three-jaw chuck round backwards by hand, although the wire is under tension and being guided over the mandrel so I can use both hands.

Photographically, and thanks for your compliment, I use a Canon EOS 300D Digital, and used some of the funds from selling my workshop, to buy a 100mm Ultrasonic macro which, as you would appreciate allows some close up work. Like you, I have a bellows (Novoflex). This couples the lens electronically to the camera, so auto focus and aperture are taken care of should this be necessary. With a good Manfrotto tripod for rigidity, I take charge of focus and aim for the usual one third/two thirds to determine what should be sharp and what can be allowed to drop out of focus. Although the rules suggest we avoid the smallest and the largest lens apertures. So, for extreme close-ups, I generally use the minimum aperture and ignore what aberrations may creep in.

Close up photography is perhaps my favourite field, and is almost always `still life’. My hands aren’t steady enough to grab those instant nature shots. I just look at the achievements of others with admiration. With my type of close-ups, there’s usually no rush, and I can take all the time I like so long as the kitchen bench is not required by my dear wife.

 

I also bought Adobe Photoshop CS3, which is an absolute delight to use, and lets me `cheat' in several ways.

 

My earlier photographic experiences were involved in burning up lots of energy taking weddings and the like. In those days I was a Leica man (35mm of course), with a pretty smart darkroom for B&W processing. Ah! those were the days.

 

Now it's time to relax and watch a bit of TV. The skeleton clock is silent for the time being.

 

Regards,

 

Sam

Edited By Sam Stones on 18/05/2011 09:31:03