Antiques and heirlooms

Among amateur watch repairers, it is good advice refuse to work on antiques or valuable heirlooms.  Doing so without sufficient experience can lead to frustration!  Old watches also have non-standard parts and other oddities that can trip up the unsuspecting would-be repairer.  I have followed this advice until recently... and ended up in a bit of an adventure.

What tempted me down this path was an antique heirloom watch that was in very poor shape.

It was apparently my great grandmother's watch.  It is quite pretty, but when I received it, it had not been well kept by its owner.  Furthermore, it had been to some very poor watchmakers!  Slowly, over the course of three years, I made a number of repairs, none too difficult:

1. I replaced the missing glass with an acrylic face.
2. The case wouldn't close because it was slightly out of round... I put it back into the round, so the case opens and closes correctly.
3. I remade a case screw that someone had snapped the head in half (!). There are marks on the plate where the screwdriver skidded off after snapping the screw, so clearly way too much force was involved.  Ouch!
4. The winding stem that was acting up, because a brake was tensioned incorrectly.
5. I put the hairspring back in order because it was twisted badly.
6. Finally, recently, I took the movement apart and cleaned it.  This was completely uneventful.

It now runs reliably, but gains about 5 minutes per day.  That's terrible, of course.  But given that I don't have a replacement hairspring and given the age of the watch, it's well within what I'm willing to tolerate.

I had a very different experience -- and it's not over -- with a watch from my wife's family.

This watch wouldn't run, but didn't have anything visibly wrong with it.  Upon disassembly, I found that the lever fork cock was ever so slightly bent and was pinning the fork down.  Since it couldn't move very well, that kept the train stuck.  That wasn't the only problem...

As I was reassembling the balance, I was a bit less careful than I should have been.  I noticed the balance was not able to turn freely in both directions.  The balance was simply on the wrong side of the fork, and needed to be carefully lifted over the fork.  Unfortunately,  I couldn't visualize what was wrong.  Instead of the correct move, I gave the balance a sound push the other way.  That was not a good plan, and I really did know better!  Disaster!  The impulse pallet jewel was shattered!

After carefully sizing the missing pallet (seems to be about 19/1000"), I realized that it would be useful to make the pallet out of blued steel.  It should have nearly the same characteristics, and it should "just work."  (I also ordered a ruby impulse pallet, but I'm not confident of my measurements...)

It took five tries to make and install the impulse pallet, because I lost the first three pallets I made, and although the fourth worked, it was very poorly made.  The fifth looks nice enough and seems to be working. 

Of course, the first step was to disassemble the balance.  I removed the old pallet by heating the roller table with a soldering iron with a fine tip at roughly 250 degrees F.  Using a needle, I cracked off all the old shellac.

First, I trued up the end of a 0.5mm blued steel rod, using an arkansas slip.

After truing, I rounded and burnished the end.  Next, under the microscope, and on a soft piece of wood, I ground a flat surface using the arkansas slip.  In the picture below, the flat is visible as the slight smear at the end of the rod.  (The flat is about 1 mm long.)

This made the rod into a D shape.  I kept grinding the flat until the rod barely entered the hole in the roller table.  Then, I burnished the flat surface.

Unfortunately, the rod was too large to fit the slot in the lever fork.

So, I ground a fine taper to the rod by hand, by eye, under the microscope until the rod would just barely bind in the lever fork as I rotated it with the tip in the fork.

Then I switched to a steel burnisher to smooth the surface of the rod.  After burnishing, the rod freely fit the lever fork, with the base of the taper still fitting the roller table.

To cut the pallet off the rod, it's important to cut it to the precise length.  Since I ended up making five pallets, I was able to zero in on the correct length by comparing with an earlier attempt.  But in any case, I reversed the rod in the pin vise, and then used a narrow file as a saw to slice off the pallet.

Once again, I switched back to the arkansas slip to true the end, and then polished it with the burnisher.  Even though this cut end is completely invisible, this was an important step because the cutting raised burrs.  Burnishing removed those burrs.

OK, now the pallet was small!  It's the apparent "grain of sand" on the left of the frame in the balance cock in the picture below.

Getting the impulse pallet into the hole in the roller table was... irritating.  The pallet is slippery by design, and rounded... which means that holding it too tightly (or gripping the wrong surface) with tweezers will launch it across the room.  I lost three attempts irretrievably and lost another one for a very long time.  Eventually I got it pressed in place.

To anchor the pallet, I gripped the balance in surgical clamps and applied shellac.

Someone before me was way too liberal with the shellac and glued together several turns of the hairspring.  I was able to knock them apart, but if it impacts timing, I may have to immerse the spring in alcohol.  I'm loathe to do that because the spring has a nice overcoil and is very, very delicate!

Here is the balance reassembled with the new impulse pin installed in the roller table.

And a zoom-in:

 
But the balance reassembly did not entirely go well the last time...  I bumped the attachment point with the tweezers, and snapped the spring at the balance attachment point.  Previously, I had thought it nice that there was a removable clamp that made removing the balance easy.  However, that clamp was installed very permanently onto the hairspring.  It took a good two hours to remove the old pin (brass, extremely tightly fit; I think it was staked in place at the factory!), fashion a new pin (I used soft copper, and much longer, since I wanted be able to get it out in the future if needed), and get everything back to working order.  As wooden clockmaker Clayton Boyer says, "Mistakes take a lot of time. I spend some of my best woodworking time making them."  Yeah, I agree.

Still, after all that, the watch still would not run.  What!?!  No visible trouble... actually, not.  I had never worked with a watch with an overcoiled hairspring.  It can happen that the overcoil turn can foul on both the balance cock and the main turns of the spring.  That was the problem.  A very slight touch on the spring attachment point fixed the overcoil's path, and the watch sprung to life!

The movement is now running, which is a relief!  It sounds different from the other movements I've repaired, because it's quite a bit lower frequency (around 2 Hz) than other movements of the same size (typically 4-6 Hz).  Assuming it all goes back together, I wonder if it will keep reasonable time?

One final thing, though.  The winding works for this watch is not the usual Swiss mechanism.  It's a bit simplified, which seems elegant at first.  Here it is when correctly assembled.

However, should the stem get loose and you simply try to reinsert it, you will likely knock the cylinder gear assembly off its retaining spring.  This is rather subtle.  In the picture below, the lower retaining spring is supposed to be running in the cylindrical groove right below it.  All you need to do to repair it is slip the stem back in, and push the spring down gently.  It reseats easily, and then you can carefully withdraw the stem, leaving everything in place.

This process is extremely annoying, because although fixing it takes mere seconds, to access this mechanism you have to uncase the movement, dismantle the hands, and dismantle the dial.  Reassembling the movement into the case involves reinserting the stem, which has a tendency of knocking the winding mechanism out of order... so you need to back up, disassemble everything and try again...

Clock 4 now runs with intermittent impulsing

"Intermittent" can be a problem, but not in this case!  Based on the numerous power budget calculations I've done, impulsing the pendulum in Clock 4 every minute is too much to ask.  After having gotten the escapement to impulse every period (2 seconds) reliably, with run times around 8 hours, it seemed like the right time to go back to trying to get the intermittent part working again.  Especially, the run times without intermittent escaping were limited by drive cord length -- I had a four fall pulley in place for the clock to run that long. 

Therefore, I added more deep cuts to the count wheel, now five in total.

This means that the escapement should be triggered every 30/5 = 6 pendulum periods, or every 12 seconds.  The pin wheel has 30 pins, so will then have a period of 12 seconds * 30 = 360 seconds = 6 minutes.  The pin wheel is driven through a 1:10 mesh for the drive wheel, so it should make a rotation every hour.  I can therefore drive the minute hand from the drive wheel, although it will run counter clockwise.

With some tuning, the Clock 4 runs with 8 lb of drive weight, directly driving a barrel of 1.2 inches.  The clock's run isn't perfect, as (1) the count wheel double counts immediately following an impulse and (2) sometimes this double-counting skips over an impulse.

But given these issues, Theodore measures the following periods in current configuration:

• 53 seconds for the count wheel

• 4 minutes 24 seconds for pin wheel

Given these measurements the drive barrel will make one rotation about every 44 minutes.  In that time, the weight will have dropped 3.7 inches. 

Thus the power consumed is:

3.7 inches / (12 in/ft)  * 8 lb / (44 min * (60 s/min)) = 9.4 * 10^(-4) ft lb / s = 1.28 mW

More power calculations with Woodward's intermittent grasshopper

By joining the count wheel pusher lever of the the Woodward escapement to the escapement trigger, you can make the escapement trigger once per period.  This is the most frequent that the intermittent grasshopper can be triggered.  Triggering every period already happened by accident, but I decided to force it to occur by linking the mechanisms together without using the count wheel.  This way, I could debug the escapement mechanism... and there were indeed problems there.  I think I've resolved them, and this modified mechanism reliably runs until the weight hits the floor.

Currently, the mechanism runs on 1 lb 14 oz, falling 3.9 inches every 10 minutes.  Converting to standard units, this means that the weight falls

3.9 inches * 25.4 mm/inch / (10 min * 60 s/min) = 0.17 mm/s
1 lb 14 oz = 0.85 kg = 8.3 N

Thus the power consumption is 0.17 mm/s * 8.3 N = 1.37 mW.

This is substantially more pessimistic than my previous figure of 0.325 mW averaged over one minute for the count wheel assembly.  This is even with an improvement resulting from a few changes I made.  The pendulum is now hung from two sharp brass points resting in brass cups.

This new hanger ensures a positive positional lock and a definite axis of rotation for the pendulum with substantially less friction than before.

I also made a number of small improvements including reshaping one of the pin wheel pinion teeth, aligning the impulse hook, and stopping the detent's fall a bit earlier.  Finally, I removed every other pin in the pin wheel, which means that the period of the pin wheel is one minute.

Update: 5/13/2019.
By clipping off the tail of the locking detent to make it somewhat more delicately balanced, I can reduce the drive weight by 6.5 oz.  Thus, the power consumption is

3.9 inches * 25.4 mm/inch / (10 min * 60 s/min) * (1.47 lb * 4.43 N/lb) = 1.08 mW.

"Hidden" power losses in Woodward's escapement

I have been thinking about how my implementation of Woodward's intermittent grasshopper is not successfully transferring enough power to run.  The pendulum power requirements I computed earlier are certainly sobering -- even though this clock's pendulum already appears to be substantially more efficient than my other clocks -- they are not the only power loss. 

Since the escapement runs intermittently, I can dramatically increase the power supplied by the escapement by repeatedly triggering the escapement.   In one experiment I tried, the triggering mechanism got jammed, which triggered an impulse every swing.  This was enough to run the mechanism until the pin escape wheel got stuck. 

But even when triggered every swing, the power supplied is only marginally sufficient, even setting aside the pendulum losses.  If I look at the amplitude immediately before and after an impulse, it's not noticeably different.  This indicates that there are substantial additional losses that occur during the triggering and impulse.

What can cause this? The most obvious (though probably not the only) energy losses are caused by the fact that it takes a definite amount of energy (force times distance) from the pendulum to move both the triggering lever and impulse hook.  Since both of these fall back to their original positions after the impulse without returning this energy to the pendulum, all of this energy is lost!  So, the return counterweights should be heavy enough to ensure a reliable positive action, but otherwise as light as possible. 

(I recall now a similar issue with Clock 3, where my initial attempt at a sprung detent resulted in too much energy loss.  Since I couldn't get the wooden spring weak enough without breaking it, I ended up opting for a light counterweight.  It's probably still too heavy, and may account for much of the need for a heavy drive weight.)

Clock 4 escapement triggers

The next step of constructing Clock 4 is the intermittent triggering mechanism.  Once per minute (one rotation of the count wheel), it triggers the impulse hook to grab one pin of the pin escape wheel.

The impulse hook was cut from the pendulum rod (mostly for aesthetics).  This version has a brass hook rooted in the block and anchored with super glue.  I later replaced this with a stiffer steel one.

The hook is counterweighted by filling the wooden block with lead.  This was sufficient for the brass hook, but not for the steel hook.  I added a screw and nut outrigger counterweight for that.  The steel hook turned out to be a good idea because the brass one was really very pliant, and was getting distorted by each impulse. 

The hook assembly rides on a brass pin on the pendulum.

The impulse hook is triggered by an assembly that sits behind the count wheel.  The straight segment gets grabbed by the count wheel driving pallet (hook) once a minute, and pushes the flat segment against the impulse hook to engage it.

I also made a wood and brass key to wind the clock.

Here is a video the escapement being triggered successfully from the count wheel.  (Hemostats are useful to keep parts in place...)

This has taken the past two days to get it adjusted.  Here is a video of an amusing -- and vexing -- fail mechanism.  Watch to the end... it gets worse!

Next up: the pendulum is indeed not running long enough (as the previous post probably suggests...).  I suspect I do need to increase the weight of the pendulum bob, regardless of the power needs, and figure out how to reduce the friction.  That first requires finding where the friction is...

Clock 4 detent works!

Remaking the detent a few times did the trick.  Each time it worked a little better than the one before, as I flushed out the bugs.  I had a scare where I damaged the gate, but a little super glue seems to be holding it together.  Here is the detent that finally does the job.

The detent properly releases one pin at a time when recoiled by hand with a weight of just about 2.2 lb on the great wheel.

I did not have to modify the pin wheel. It is helpful to have a banking so the detent is held in a convenient position if all the weight is removed.  This also gave a good opportunity for testing the winding mechanism, which does indeed work.

Clock 4 detent issues

I installed a new(er) 1/3 hp 1725 rpm motor on my lathe since the bearings on the old one were dead.  It runs much better than before!

The detent mechanism for Clock 4 uses a gate invented by Philip Woodward (I think).  The detent sits on a pivot near the pin escape wheel.

The detent is fairly long, but just press fit into the frame.

The detent is cut from a small piece of white oak.

Here is the detent after shaping.

There are many issues with the detent, and it doesn't run at the moment:

• The gate is very thin.  I broke two detents already
• Woodward didn't seem to bank his detent, but it looks like I need to since wood has more flexibility than metal
• The catch for holding the pin is very touchy as to how deep it is.  Woodward suggests that it might work as just a small depression, but this caused the pins to jump out.  Too deep, and they can't clear when the escape wheel recoiled... in which case the pins stick.
• The pins of the escape wheel are too inaccurate in their placement
• The pins of the escape wheel are too inaccurate in their vertical alignment
• The pins of the escape wheel are not all the same diameter (because some of them split in the process of being installed).
• The relative positioning of the catch and the gate slot is quite delicate, and there isn't much clearance.
• The counterweight portion of the detent governs how much weight is needed to run the escapement.  This needs to be very light.

A few times, I could feel the escapement "almost working" under my hand, but it wasn't consistent enough to run under a weight.

Clock 4 pin escape wheel

One of the defining features of Woodward's intermittent grasshopper escapement is the large pin escape wheel.  It is intended to be let off once every minute, so there are sixty pins.  After considering the possibilities for how to index, drill, and make the pins... here is how I proceeded.

Since I print the pattern and glue it to the wood, indexing is "sort of" not a problem.  I started by center punching each pin location.

Since I don't have a drill press, I set up the lathe to index each of the punch locations and drill as well.  The spacing between pins may be accurate enough, because when the drilled holes make their way around to the indexing pin, they're slightly off from the center punch dents.  But it at least this setup ensures that the pins are all the same distance from the center of the wheel.

After initially thinking of steel, then brass pins, I decided that metal pins might be rather loud.  So instead, the pins are made from toothpicks.  They are roughly cut to the right size.

Then they're staked into position...

... the end sticking out the bottom clipped off ...

... and then carefully planed flush with a chisel. 

After all this, I went through and cut off any pins that were longer than the rest, probably to within a 0.5 millimeter or so. 

Here is the escape wheel trial fit in the frame.

Count wheels and pendulums

Philip Woodward invented many interesting clock mechanisms, which are based around intermittent escaping.  To time the intervals between impulses, his escapements use count wheels.  But he cautions that a poorly-designed count wheel can dramatically alter the Q of the pendulum, and cause reliability problems.  Since my next clock is planned to use Woodward's intermittent grasshopper, impulsing once per minute, I wanted to make sure that the count wheel worked well on its own.

Realizing that my previous clock #1 pendulum has a low unloaded Q because I chose to suspend it in a plain brass pivot, I tried a knife edge suspension.  To hang the pendulum, I took a piece of wood with a branch at a right angle and shaped it into a strong bracket.

The bracket has a slot cut into it to receive the pendulum's knife edge. The pendulum knife edge is crude at this point, and not very artistic.

Unloaded, the Q is around 300-500 with some steel weight I tied onto the bottom. 

For the count wheel, I cut a simple 30 tooth ratchet wheel from 1/8" plywood.  I tried to get the tooth spacing about what would correspond to a degree or two of pendulum amplitude about 6" from the suspension.

The count wheel is driven by two wire lever pallets.

The left pallet attaches to a hole in the pendulum and pulls the count wheel to advance it. The right pallet attaches to a separate anchor point, and serves as the backstop.

Here is the assembly, ready for testing.

Starting from a comfortable amplitude, which pushes the backstop about halfway back, the mechanism will run reliably for somewhat longer than 2 minutes.

Starting from just below an amplitude causing double counting, it will run for over 3 minutes.  This is heartening, because it indicates that impulsing every one minute is feasible, because there is plenty of extra energy available to let off the escapement (not built yet).

Clock 3 torsion pendulum updates

I made several updates to Clock #3 over the weekend... in the end, it is running with about 1.75 inch-pounds of torque on the center wheel. 

Paradoxically perhaps, I found that it runs better with the right angle transmission meshing at the top rather than the bottom...

But then I found that the pivot below was unnecessary.  This reduced friction somewhat, and lengthening the pivot considerably was helpful. 

Initially this seemed to reduce the needed torque to around 1 inch pound.  With two pounds on the balance (one pound is shown above), this seemed very stable.  The center pivot was set in the wood frame.  Unfortunately, but since I had to make several drillings to get the depth correct, the hole walls were weak and eventually split.  So I inserted a brass bushing...

This bushing was not depthed correctly, so I had to drill out and shim the hole, so it looks less nice than it does above.  With the bushing, the running torque is back to 1.75 inch pounds...

Additionally, I found that occasionally the escape wheel would skip.  The reason is the when the wheel rides up on the locking detent (black arrow), it deflects the detent too far and the wheel slips past...

Clock #3 at least runs!

Clock #3 has been plagued by various problems, mostly with the resonator/balance not being really suitable.  One of the things that was exacerbating matters was the passing spring on the detent was still (even after modifications) too stiff.  I went back to various books and found that the passing spring tended to be quite long, passing beyond the locking pallet.  So I modified the spring in that way.  Now it's much lighter.

I thought long and hard about the balance issues, and came to the conclusion that I probably had to face a right angle turn and a torsion balance.  You can see the new right-angle transmission wheel above on the impulse roller assembly.  The other half mounts to the balance through a spring, which consists of a spring, a rod, pin, wheel, and balance (at the bottom of the rod).  Here are the pieces...

... and here it is assembled.

The balance hangs in front of the lower section of the clock frame.  The rod passes through a pivot, which is formed from a steel wire.

This is perhaps not the best option, but it has the merit of making it easy to adjust the depth of the right-angle transmission.  The transmission runs fairly smoothly and noiselessly.

To first approximation, the new balance appears to have a resonant Q of around 12, whether loaded or not.  (Eyeballing 3 periods before the balance amplitude halves, then multiply by 4 according the rule of thumb suggested by Woodward.)  So the pivot and transmission is the least of my concerns, but the fact that the unloaded Q is low is definitely an issue.

The mechanism appears to run semi-reliably...

but it needs considerably more torque than I'd like.  The center wheel needs about 4.125 inch-pounds in order to maintain balance amplitude.  This is concerning because I was really hoping this to be the torque on the drive wheel -- a factor of 10 weaker!  The resonator having so much absolute loss of power is clearly a problem.

Lower on the priority list is the fact that with this balance the clock runs a bit fast.   It makes 17 "loud" ticks per minute rather than 15.  That should be easily corrected.

Clock #1 summertime adjustments...

Clock #1 has been in our dining room since I moved it upstairs since March 11.  It ran for several months, and then in mid-April started to become unreliable.  I suspected weather factors were the cause.  After running from mid-April until mid-May, it stopped again, this time apparently for good.  After letting it sit for about 10 days, I went back to investigate the issue.

The overall friction appears to be higher in the spring/summer (though I don't know for certain), although it's unclear exactly if this is localized to a specific mesh in the train..

It seems that the problem was that a few escape teeth were too long by a very small amount (8/1000").  When the friction is lower in the train, the pendulum amplitude is high enough that this doesn't matter.  But when the amplitude drops, this becomes a problem.

To debug the problem, I stuck a post-it note to the back of the frame behind the pendulum.  I marked on this paper the precise pendulum location when each escape tooth released.   The marks were about 13" from the pendulum pivot, and indicate that the typical distance between entry and exit release was 3/16", or about 0.8 degrees peak-to-peak.  So if the pendulum swings less than that, the clock is likely to stop.  I found that one tooth that seemed to cause stoppage consistently corresponded to a mark 1/16" farther out from the rest.  This means that an additional 0.15 degrees was necessary to escape that tooth.  Since the anchor has a length of 1 3/4", this translates to an escape tooth of about (1/16)*(7/4)/13 = 8/1000" longer than the rest.  That's a very small amount, but easily corrected with a file.  Once I corrected that, I checked each other tooth as well, adjusting them so they were all within the 0.4 degree peak-to-peak release margin. 

It seems unlikely that expansion or contraction of the escapement itself (due to weather) is the cause of the clock's malaise, especially because that particular tooth was already marked as being problematic in the past!  Hopefully, my guess about balance amplitude is correct, because it seems to also explain the other issues about the escape wheel sitting at the front/back of the clock too.  This slightly shifts the escape wheel up/down by a very small amount and seems to change the effective length of the escape wheel teeth by a few thousandths of an inch.

Clock 3 escapement adjustments

By using the strategy of topping-within-the-frame, I got the escapement wheel for clock 3 round.  That helped a bit.

By filing the foot spring on the detent thinner, I got it so that 2 lb tangential force on the center wheel got the clock to run.  Still way too much.  So I kept filing, and the spring got very delicate.  I didn't break it, but it was no longer stiff enough to stay vertical.  So, time to make a new detent. 

Figuring that detents were delicate, I made two: a spring one like the one I over-thinned, and a pivoted one. The pivoted detent consists of two parts, a pivot, which attaches to the cock, and the detent itself.  The detent has a counterweight instead of a return spring. Here are the parts, with no springs...

... and here is the pivoted detent assembled. 

It wasn't hard, but required a little thought.  The pivoted detent is much easier to adjust, but even a bit too light.  A few tenths of an ounce on the counterweight seemed to help.  But I broke the pivot hole, so I'll need remake it.

As for the rest of the clock, the idea of a 4-second period for a compound pendulum with a small radius is not going to work.  The longest I can get is about 1.5-2 second period with no escapement in place.  So this means the gearing will be all wrong...  Perhaps this clock too will be a timer.