Member postings for Sam Stones

One evening in October, when I was one third sober - or so the story goes, I decided many years ago to build author John Stevens’ "A Skeleton Clock with Lever Escapement" (see five editions of ME commencing Feb '72). She, who must be obeyed, was unprepared to have a model beam engine on the mantelpiece.

With one eye on "Watch and Clock Making and Repairing" by W J Gazeley, my attempts to make a bi-metallic balance wheel for this clock may perhaps be of interest and/or amusement to other model engineers. Or perhaps get a smile or two from any horologists who might be `listening’.

Making this wheel, I have to say at the outset, took five attempts before I achieved an acceptable result. For my personal satisfaction, every part of this clock had to pass close examination through a 4" binocular magnifier.

The method advocated for attaching the brass to the steel (see page 243 of Mr Gazeley’s book) was to turn a `sink’ into a rod of `good-quality’ steel. A sink in this context is turned into the end of the rod, thus forming a circular groove with a rectangular cross-section, and whose inside diameter exactly matches the diametral interface of the brass with the steel. A ring of brass is machined whose volume will more than adequately fill the groove (sink) once the brass starts to melt. During my last attempt, and allowing for the borax paste, the brass ring was a close (tight) fit onto the inner side of the groove. Presumably the brass ring would loosen up as it got hot. This inner face was to become the steel/brass interface.

By the way, and this may be obvious, the brass must be on the outside of the finished wheel for the principle to work. The normal ratio for brass to steel (as stated) should be 3:2, although mine ended up at about 2:1. If it doesn’t keep good time in Melbourne’s wide temperature fluctuations, at least it should look good.

Even though I did all the right things (or thought so), each earlier attempt revealed either poor fusion or blow holes, once it was back in the lathe. The essential issues related to perfect cleanliness of all the parts including the borax and water needed as a flux. I didn’t have a hot source of heat at home, so I went into the maintenance department of the office where I worked, and they sprayed a nice hot oxy flame onto the assembly. An acetylene flame burns very hot, so maybe the earlier attempts got the brass too hot, I’m not sure.

Mk V balance wheel was eventually ready for the bench, so the next step required piercing and filing the bottom face to form two crossings. For some unknown reason, in clocks, they are called crossings not spokes. A couple of holes are drilled in the spokes (sorry crossings) near the centre so that the wheel can be attached to the balance-wheel collet with two tiny screws. Finally, the rim is cut through close to where the crossings meet the rim so that two semicircular `bands’ are created. These form the bimetallic `arms’ which is what all the fuss is about. That’s where it stands at the moment.

Regards to you all,

Sam

The skeleton clock I am about to finish, is timed by means of a bi-metallic balance wheel and a helical spring, and driven via a lever escapement and pallets. The section of the spring as design by author John Stevens (see "A Skeleton Clock with Lever Escapement - ME Feb '72 "), has a width of 0.020" and a thickness of 0.005".

With very limited workshop facilities, and not thrilled with the idea of trimming a wider strip of spring steel, I wondered if I could instead substitute round (piano) wire for the spring of the balance wheel.

Roger, Jim, Peter and Terry - Thanks to you all.

Once again, as a rather Nervous Nellie, (I’m repeating myself), it’s because the machinery does not belong to me, that I feel bound to proceed with caution. Additionally, I have to drill a few more relatively tiny holes into the engraver’s brass scrolled plates of the skeleton clock, and the thoughts of damaging these hand fretted, filed and polished items gives me the Willies. With due respect to all the Willies!

Also, since selling up my workshop and all that went with it, I’m very limited in materials (drifts and other `knocking-out’ devices).

With respect to the BFE 65 MT1 (#1 Morse taper) lock-up, when I saw how small the thread was on the end of the draw bar, it concerned me that too much thumping might strip it. Making a new one on the HobbyMat lathe with its rather limited screw-cutting facilities, is not a sensible option for me.

I suspect that the mill `chuck’ had not been used for some considerable time and, judging from the rust (or some other substance) around the MT1 stem, the need for penetrating oil turned out to be more than necessary.

In closing, you have also brought back memories of locking-tapers and coefficients of friction.

Keep up the good work.

Sam

After much soaking (four days) with penetrating oil, and then several swift blows onto the centre of the Allen-screw end of the draw bar (almost fully engaged into the thread), I finally persuaded the milling cutter collet head to let go.

Many thanks,

Sam

To everyone reading this thread, I agree entirely with Alan Gray 1, when he suggests that I made an error in introducing the bench test. In advising Versaboss of the dangers associated with polyacetal, I made too strong a point.

Although the technique is well documented in several raw material suppliers publications, including the multi-national company I worked 24 years with, I should NOT have gone so far into this subject.

Thanks to the help of several other readers when I was researching the archives, it was described in five issues of Model Engineer.

The first edition was dated 4 February 1972. The copies with the above clock are, Vol 138, issues 3434, 3435, 3437, 3438, 3439.

I hope this is a good starting point.

Sam

I’ve just been glancing through some of the threads about clocks, and am reminded of the time when I was cutting the 96 tooth Great Wheel for John Stevens `Skeleton Clock with Lever Escapement’.

That was back in the early 70's and I’m now 75, so please excuse any dithering in my notes.

With the second hand Myford ML7 which I bought around the early 60's came a home-made dividing head with three plates. The ratio of the worm and wheel was the usual 40:1.

I was convinced that I had set up correctly so that the end result would display 96 teeth on a wheel measuring about 69mm diameter. This wheel engages with a lantern pinion so I took a chance and ground a fly cutter with a profile that might just pass as an involute.

I merrily progressed around the brass blank, and with manly pride, chose to check that the final move `into the first slot’ would prove that all was well. It wasn’t!

Before my eyes, the first tooth disappeared. Out came my Machinery’s Handbook from which I was to discover that with the plates I had, I could only divide to give 94 teeth.

Oh dear! or words of a similar meaning.

Then came the break-through. Of all the wheels in this particular clock, the number of teeth on the Great Wheel was not critical. Ninety four teeth was OK, so that’s where it rests.

Perhaps I’ll drop a Forum thread about my efforts at making the balance wheel.

I welcome any comments you chaps have to offer.

Sam

Versaboss wrote :-

Hi Steve,

Many thanks for your quick replies which were over night for me in Australia. I was about to send my reply to your first two messages until I discovered your third one. This is what I was about to say :-

Yes, I’m inclined to agree with you that it’s muck, especially since the only parts now involved are the top-slide lead-screw, the nut (keyed into the rotary bracket with a tiny grub-screw along its edge ), and the rotary bracket (wheel?) used for indexing the top-slide around when taper turning.

The jamming appears to be around the tip of the lead-screw inside the rotary bracket, and I’ll only find that out by removing the nut. Since it’s not my machine, I’m rather concerned that the lead-screw may have partially seized, and that removing the nut may introduce another problem. Like a bad tooth, it has to come out.

When the garage gets a bit warmer this morning, I’ll try to `persuade’ the lead-screw nut to come free. With the grub screw (key) out of the way, I plan to use the tail-stock and a short length of rod to push on the end of the lead-screw. It’s been left with a centring hole so I should use a corresponding rod tip to avoid damaging the lead-screw tip.

Amongst a variety of changes, and if the machine were mine, I would plug the clearance hole for the stop-slide lead-screw since it is ideally placed to catch swarf.

I also agree with your comments about the gib strips which have been cut away in several places to provide flat seats for the adjusting screws. They are weakened as a result, and are prone to bending. And, if the screws are not located correctly, the strips do appear to jam.

My concerns about the back-lash were largely in relation to the possibility of a second nut inside the rotary bracket, whereby the back-lash would be reduced during manufacture. As you indicate, it's not the case.

As an addendum in response to your third reply:-

I agree that the alignment should be done with the lead-screw wound in as far as possible such that the best alignment is achieved. The fixing screw clearances through the end plates allow for this. I was actually up to this stage when the jamming occurred . Because of the tendency for the gib strips to move/bend, I was more inclined to adjust their final sliding fit before the lead-screw was in position (a method I’ve used when I had my well-loved Myford ML7). Rather than winding the lead-screws in and out, it is much quicker to be able to push the slide to and fro.

Thank you for your patience Steve.

Best regards,

Attention HobbyMat owners, I need your help.

I’ve managed to borrow one of these lathes to help finish my skeleton clock.

The machine had stood unused for some time, and needed a good clean to bring it up to clock making standard. In the process, I decided to free up various working parts and reset the slide clearances, etc.

All went well until I came to the top slide. On the bench, the top-slide lead-screw fitted into the nut OK, and initially during assembly onto the lathe.

I was surprised to discover that as the tip of the lead-screw reached the pivot pin, the lead-screw began to tighten and will now only move a few turn in and out before it locks up either way. I lowered the pin slightly to clear the lead-screw tip, and at first this appeared to work.

As you will know, the visible part of the nut is eccentric with a grub-screw `keying’ the nut in place. Looking from the other end of the lead-scrw, there is nothing to go on. 

Is there some sort of back-lash adjustment with this arrangement which is causing the problem?

Tucking a bit of emery cloth under the drill/cutter probably works by sitting under the back rake, and both damping the vibration and rubbing off the chatter marks.

I like Ian S C’s idea of modifying the head of the screw. With a counter sink (drill) the same dia as the screw head, and thus forming a step, the screw can be made to sit flush with the work piece. When using Allen screws for laboratory instrumentation, besides adjusting the head size, I often rubbed and polished off the blue finish.

Good luck.

Sam

If you like your work to look good and/or have a professional appearance, here’s another idea which removes the hassle of counter-sinking. Drill the counter-sink first!

It’s a technique I've used for many C/S situations, and which provides a near perfect looking result whether or not the C/S screw is in position.

It assumes however, that you are both unperturbed by altering the tip of a twist drill AND that you are capable of sharpening drills by hand.

Select a drill which is only just bigger than the head diameter of the C/S screw. Sometimes there are drills which sit in the drill stand that hardly ever get used. Even if the selected drill has to be used in a hurry later, it will still work.

Instead of the usual 30 degrees, grind the tip of the drill to 45 degrees to match the underside of the screw head. A further improvement which I alway use is `pointing' the drill tip on the corner of the grinding wheel, effectively thinning the drill web. Some practice is needed to get this right, but it’s worth the effort. Go easy with backing off (lip relief angle), a reduced angle goes towards improving the finish. When you get the geometry right, it's almost impossible for the drill to chatter.

There’s more good news. It’s easier to see the drill tip, you can use normal drilling speeds, and you can still drill into virtually any normal workshop material.

On the down side (there has to be one!?), a little care is now needed with a normal 30 degree drill when starting to drill the clearance hole for the screw body.