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S Haller “Elo” midget escapement question

whatgoesaround

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As Wayne said, flipping the fork often has worked for me. The block that holds the fork is arranged so that the greater mass is below, if attached as shown in the guide. By flipping, you then have more mass above the fork's location, thus shortening the amount of suspension spring between the fork's block and the top block, if that makes sense.
 

KurtinSA

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I got to thinking about the notion that relying on the suspension spring above the top block to deal with flutter is not something I've considered. That part of the suspension spring needs to be the proper dimension...to use something thicker or to thin to a bigger dimension doesn't make sense. Control of flutter should focus on other aspects of the escapement. Generally speaking, if the escape wheel falls solidly on the lock surface, you shouldn't get flutter. So, ensuring that the locks and drops are correct is the first goal...then maybe tweaking the locks a bit could be considered...too much lock result in too much drag, though.

Kurt
 
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victor miranda

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I get the impression that the thinner the suspension, the more prone to fluttering the escapement will be. It seems that flutter is prevented by having a shorter length of spring between top block and fork, which damps the fork’s movement.

When I thinned the suspension, I thinned it all the way up. I’ve read of others who thin from the fork downwards, which in the light of my experience could be a better option.

Anyway, for what it’s worth, the clock is currently keeping perfect time, so hopefully this can be the end of the matter! Thanks for everyone’s helpful input.

Phil
Hi Phil G4SPZ,
the clamping of a fork onto the suspension spring creates two springs.
the top spring is what the escape drives. as you noted.
I promise you can make that top spring so short and stiff that the escape will never drive through it.
your conclusion is what I had decided, in practical terms, raising the fork will stop flutter.
if not, the escape needs attention.

thinning the entire spring is what I think good practice.
I can't tell you either way is somehow better.

a note about threads.
I think repair threads have a normal arc where the repair
is given first consideration and a bit of care is taken to
help and point in the most likely direction.
once the repair is done, quite often the discussion goes into
understandings for surround topics or why some alternative repairs were not done,
or perhaps are poor options for this clock.
so we are in the post repair comments.
you are doing great!
 
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Phil G4SPZ

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Hi Kurt and Victor,

Yes, I’ve seen the opinion expressed that the spring should be uniformly thinned. Equally I have seen from others who report success thinning from the fork downwards.

However I wonder in what way the small section of the spring between the top block and the fork is claimed to be most critical? Logic says that the suspension spring will normally be the same thickness along its entire length, as it would be if you fitted a brand new spring. Yet the rate of rotation or natural resonant frequency of the pendulum assembly depends on the weight and diameter of the bob, and the torsional resistance of the suspension spring. By thinning the spring, we reduce its resistance to twisting and slow down its period of rotation, much like fitting a softer hairspring to a clock balance.

Now, the short bit between fork and top block is only a tiny proportion of the full length. To prevent flutter, this needs to be relatively ‘stiff’ compared with the main section of the spring which largely determines the rate. As Victor notes, we have effectively divided the spring into two separate sections, by fitting the fork.

All I am suggesting is that there could be certain sets of circumstances where thinning a spring only below the fork might be a more appropriate option, or at least equally acceptable. The current circumstances of a very thin spring, high power at the escapement, a high fork position and a tendency to flutter are a case in point.

It is indeed an interesting debate and I’d like to offer to experiment, but having got my clock working so well I’m inclined to leave well alone!

Phil
 
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Phil G4SPZ

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...Control of flutter should focus on other aspects of the escapement. Generally speaking, if the escape wheel falls solidly on the lock surface, you shouldn't get flutter. So, ensuring that the locks and drops are correct is the first goal...
Interesting thought, Kurt. However, experience shows that if we start with a perfectly adjusted and functioning escapement and we move the fork too far down the spring, the escapement will flutter. By definition, there’s nothing wrong with the escapement; all we have done is reduced the resistance that it’s working against. Raise the fork to its original height, and the fluttering stops. Again, all we’ve done is increased the resistance on the escapement, by shortening the upper portion of the spring.

The other thing that changing the fork height does is change the amount of twist imparted to the bob, because the fork will be moved through a different included angle depending on where it is driven along the length of the anchor pin. Hence the correct height for the fork on any particular clock is that which gives good total swing, adequate overswing and zero risk of flutter. The practical problem in arriving at that ‘sweet spot’ is that fine adjustments of fork height are very difficult to make in a controlled manner, and can’t be made while the clock is running in order to observe the effects in real time. I suspect that most clocks will run satisfactorily within a small range of fork heights. A certain amount of luck is also involved!

Phil
 
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KurtinSA

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Well, I did say "Generally" and "...the first goal"! Yes, raising the fork does tend to reduce flutter...all other things the same. I think what happens if the fork is too low is that when the fork is turned by the rotation of the suspension spring from the turn of the pendulum, the arm of the anchor pin that is being acted on by the fork is small and doesn't move enough in order successfully lock. At least that's the way I think about it. So, there are geometry aspects to this...not just stiffness of springs, etc.

Kurt
 

Phil G4SPZ

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That’s certainly one good theory.

Having seemingly spent many hours watching both Graham and pin pallet escapements, I’m more inclined to think that the fork ‘bounces’ at the point of impact of the EW tooth as it locks on the pallet, jerks the anchor pin backwards and flips the tooth out of lock. The next tooth skips past and locks against the pallet, which by this time the fork has moved deeper into the EW due to the continuing overswing of the pendulum.

Preventing fork ‘bounce’ requires the upper portion of the suspension spring to exercise more control over the fork position. The shorter the spring, the more resistance against uncontrolled fork movement. Ultimately though, as Victor says, if it’s too short its torque will match the force generated at the anchor pin by the impulse phase, and the escapement will stop.

It strikes me that most escapements will flutter if too much power is applied. I can induce flutter on my cuckoo clock’s recoil escapement by adding weight. The power overcomes the force due to gravity acting on the point where the pendulum hangs from the leader, which is mechanically analogous to the point where the fork hangs from the upper portion of the suspension spring on a 400-day clock.

Phil
 

Wayne A

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. Equally I have seen from others who report success thinning from the fork downwards.
Success here may depend on just how far you need to go, if your relatively close to regulating no doubt this method would work. Actually I have done this once when I just needed a little more and did not want to take the suspension off again.
 

KurtinSA

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If your locks are microscopic in length, the movement's going to have a tough time working. There has to be some reasonable depth the lock.

Kurt
 

Wayne A

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Preventing fork ‘bounce’ requires the upper portion of the suspension spring to exercise more control over the fork position. The shorter the spring, the more resistance against uncontrolled fork movement. Ultimately though, as Victor says, if it’s too short its torque will match the force generated at the anchor pin by the impulse phase, and the escapement will stop.
Would add that by moving the drops with deeper locks creates more tension on the spring at the point of the drop which also reduces flutter. Well this only works if you have enough swing to give away some over swing. There is a range of settings between the fork and locks that will work on most clocks, some clocks are very picky though.

Wayne
 

Phil G4SPZ

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Thanks for all the comments.

I guess most of us ‘walk’ the escapement through its action, to check the locks etc before fitting the fork and suspension. All we can do is try to ensure that the lock is sufficiently deep. In all but one of the 400-day clocks I’ve worked on, someone had previously adjusted the eccentric and/or the pallets, and restoring the correct settings was tedious although ultimately successful.

However, moving the anchor pin slowly by hand doesn’t fully replicate how the escapement will behave when loaded by a resilient spring-loaded fork.

The Graham and pin pallet are different when it comes to overswing. In the Graham, the fork has to push the pallet deeper into lock and bring it back out again, against the relatively constant resistance of the pallet’s lock face rubbing against face of the EW tooth. In the pin pallet escapement, the pin is pulled deeper when going into lock by the slope on the EW tooth, but has to recoil the EW slightly against mainspring torque in order to release the pin and unlock the EW for the next cycle. Hence the drag on the pendulum is asymmetrical going “into” and coming “out of” lock, although it’s the same on both directions of swing so the effects cancel out.

One other thought that has occurred to me is that a heavy fork would be less likely to cause fluttering than a lightweight one. The fork only needs to accelerate slowly, so additional mass would tend to reduce ‘bounce’, but I’ve no way of testing this theory at the moment! I’m guessing that a solid ‘block-and-pins’ fork might be better than the more common lightweight brass forks. Someone else may have experience in this area.

Phil
 

Wayne A

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One other thought that has occurred to me is that a heavy fork would be less likely to cause fluttering than a lightweight one. The fork only needs to accelerate slowly, so additional mass would tend to reduce ‘bounce’, but I’ve no way of testing this theory at the moment! I’m guessing that a solid ‘block-and-pins’ fork might be better than the more common lightweight brass forks. Someone else may have experience in this area.
Phil, I've also thought about this and arrived at the same conclusion, little more mass in the fork should help dampen flutter.

Now the only thing I have seen written about fork weight was that Kundo switched to aluminum forks because it reduced shipping damage to the suspension spring which only makes sense for a seller of clocks. I'm not a fan of these aluminum forks because they seem to wear more. My favorite forks are the block and pin because the pins wear little and once the gap is set it stays set every time you change fork height.

Testing the heavier fork theory might be easy enough. First you need a flutter prone clock then add a bit of crimp on fishing weight in the clamp area.

Wayne
 

Phil G4SPZ

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I’m glad we think alike, Wayne! There are many reasons why flutter occurs, but I certainly wasn’t aware that Kundo forks were made of aluminium. The ones I’ve seen are brass in colour, probably an anodised finish to confuse the unwary. As you say, this only benefits the manufacturer and certainly does nothing to help the repairer several decades later, and would seem to increase the likelihood of flutter in clocks so equipped.

What I’m tempted to do is buy in a few block-and-pin forks and try them on any future flutter-prone clocks I get in for repair. There are bound to be some!

Phil
 
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Wayne A

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Phil, the aluminum forks are unfinished so no mistaking them and it was only on there last versions.
 

shutterbug

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It's a good idea to have several sizes of suspension springs, blocks and forks on hand if you work on a lot of these types of clocks :)
 

victor miranda

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the causes of flutter...
from all I have tried and I do not claim to have trialed all the possibilities...
conclusions are; if raising the fork does not stop the flutter or the clock,
there is a 'lock' issue to resolve.

the explanations include that I noticed any changes to weight of the fork didn't stop the flutter.
small arc swings cause or allow flutter...
and twang-ie-ness on the drop seems related to good power buuuut raising the fork does not often stop it.
I think this is a drop/lock/impulse-face interaction.

what I can't say is that the pivots are involved... in that I have tried repivoting and the clock did flutter.
a little less and any is a problem.

so flutter is an adjustment issue and after you have adjusted to limits, it is an escape issue.

I have no way to polish the anchors... and my pin pallet clock does not flutter so I have not
given that type an anti-flutter study.
victor
 

Phil G4SPZ

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It is also interesting to note that most perfectly-adjusted 400-day clocks will flutter when turning the hands forwards, i.e. simulating excess power at the escapement.

Taking the earlier point that the suspension is effectively in two parts, there appear to be two resonant frequencies at work. The low main one, determined by the full length of the spring and its bob (8 or 10 BPM or whatever) and a much higher frequency which is largely determined by the mass and length of the fork together with the torsional properties of the upper part of the spring.
 

Wayne A

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It is also interesting to note that most perfectly-adjusted 400-day clocks will flutter when turning the hands forwards, i.e. simulating excess power at the escapement.
Because of this forced flutter I only adjust my clocks at end of swing where it will not flutter when adjusted due to the torsion load on the spring. If it needs allot of adjustment I catch and hold the pendulum at end of swing. Its why moving the drops apart helps to stop flutter as well, more load on the suspension spring.
 

Phil G4SPZ

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Its why moving the drops apart helps to stop flutter as well, more load on the suspension spring.
I’ve been doing some more thinking about power and flutter. The escape wheel is unlocked by the pendulum bob swinging back towards its centre position. The impulse face of the pallet (or escape wheel in a pin pallet escapement) is then free to drive the fork. If the fork moves too quickly, it can bounce back at the end of the impulse, because the main length of the suspension spring hasn’t had time to rotate far enough beyond the central position, and pulls the pallet out of lock before it has had chance to lock the EW tooth firmly. This triggers the flutter, which continues until the pendulum has swung far enough to create enough tension to damp the flutter.

I guess the logic is to keep the EW locked until the pendulum has swung far enough, so deeper locking together with a high fork position should both help to prevent flutter. It sure is a fine balance. The issue with the pin pallet escapements that I have worked on is that in most cases, the depthing is fixed, making the condition of pivots and pivot holes rather more critical.

Phil
 
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Phil G4SPZ

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After much head-scratching, I believe I’ve finally cured the flutter. I had to elongate the holes slightly to allow the top bracket, which carries the anchor arbor’s back pivot, to sit slightly lower on the backplate, thus achieving marginally deeper locking.


Phil
 
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Wayne A

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Good to hear its been defluttered! I've had to alter a bridges holes like that before, guess sometimes the manufacturing tolerances add up against us.

Never had a pin pallet flutter on me, probably because there all low powered midgets. Now trying to get them accurate, still working at that..

Wayne
 
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Phil G4SPZ

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Hi Wayne and thanks. This is only my second pin pallet and I am amazed at how much power this one has got at the escapement. As you say, the flutter must be due to a combination of tolerances, wear and other factors, one of which is the thinned suspension. The other of course is that I had to replace the exit pallet after I broke it.

I used pivot steel, and with hindsight a hardened sewing needle would probably have been better. The pivot steel is very slightly ‘springy’ compared with the original. All good experience though!

What standard of timekeeping are you aiming for? I’m happy with a minute per week, but you can probably get closer.

Phil
 

Wayne A

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What standard of timekeeping are you aiming for? I’m happy with a minute per week, but you can probably get closer.
Phil, I'm looking to obtain a minute a month or better. I've had pin pallet Schatz Jum7's achieve that for a few months but they always begin to drift. Thinking of trying a different mainspring lube on one soon.

Have a Jum7on the bench that I'm trying to set the minimum over swing to see how that works out. Reasoning behind that is to stop the pallets from moving deeper after the drops.

Wayne
 

Phil G4SPZ

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A minute a month? Many quartz clocks don’t achieve that, so it’s really good!

Long term drift has got to be a function of reducing spring power, which translates into reduced overswing amplitude. You would expect that to change the rate. Technically it should go faster as the swing reduces. Some people advocate winding anniversary clocks up every one or two months. I suppose the ideal would be to wind up the spring half-way, then set the rate, then give the key one full turn every two months. 400-day clocks were never known for their timekeeping, but given Horolovar temperature-compensating suspensions and keeping the clock at a relatively constant temperature, it’s only the reducing spring power that can change the rate.

I would worry about not having a good degree of overswing, but it will be interesting to hear the results of your experiments!

Phil
 

Wayne A

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Time for a new quartz if it will not keep better time than that! :)

Seen some unexpected behavior on pin pallet clocks. While running a rate trend on properly set pin pallet then stopping and adding additional swing by hand it will run fast until the swing settles back. Done this with dead beats and rate is not affected. So if I make the observation that pin pallets rate is affected by swing then steady spring torque is more of an issue. I don't fully wind mainspings, try for about 80%.
Now if the error was always slower the further you go into the mainspring run I'd be ok with it, sometimes if gains sometimes looses.
 

Phil G4SPZ

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I have a ‘theory’ that a dead-beat escapement applies a slight braking effect to the pendulum’s overswing, as the pallets slide across the locking face of the EW tooth. As the mainspring unwinds, the amount of impulse reduces, BUT at the same time the amount of friction between the sliding pallet and the locking face of the EW tooth also reduces, because of the reduced torque at the EW. The two effects tend to cancel out, leading to a degree of self-compensation of pendulum amplitude along the bulk of the mainspring’s run.

This theory also holds for recoil escapements, by a similar argument.

Again, this is only my own theory, although I think I’ve seen similar things written about the Swiss cylinder and other frictional rest escapements.

The pin pallet is more akin to the recoil escapement, as the EW has to be pushed back against mainspring torque by the pendulum’s overswing in order to unlock the pallet, but I guess that a similar compensating action occurs here too.

Phil
 

Phil G4SPZ

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After running perfectly well and keeping good time for several days, the flutter returned... and I caught it in the act. So I got fed up with it and decided to try to sort it out once and for all.

Having achieved deeper locking, the only other adjustment was to raise the fork a fraction more. I did that, and the flutter disappeared. All ran well with almost 360 degrees rotation and good overswing for a couple of days, until inexplicably the clock stopped at 8.40 one morning. It had drifted slightly out of beat, and I’m guessing that the effort of lifting the hands reduced the swing amplitude till it failed to unlock. Anyway, re-setting the beat very carefully seems to have put things right.

For the time being, at least. This has certainly been the most tricky midget I’ve worked on.

Phil