Sunday, March 26, 2017

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.

Sunday, March 19, 2017

Clock 3 update

As suspected in the previous post, the foot spring in the detent is driving the insane need for weight in clock 3.  I thinned it some more, and the required tangential force on the center wheel dropped from 3 lb to 1.5 lb.  So that's heartening.  The detent is now super delicate!

Additionally, since the weight requirement was lessened, the speed of action was reduced.  I therefore caught the escapement fouling... It seems that it's not that the escape wheel teeth are spaced incorrectly.  However, the detent releases the tooth early sporadically.   I think this is made worse as the spring is made weaker, as the detent isn't sitting in its banking.  The early release appears to occur more-or-less consistently at the same escape teeth, so perhaps they're slightly shorter than the others.  In any event, I had filed the detent pallet a bit and now regret doing that!

Clock 3 closer to running

I made a few adjustments to clock 3, and it's now a bit closer to running:
  1. I rounded up the unlocking roller, so that the detent unlocking spring doesn't foul on it.
  2. I filed the foot of the detent to ensure that it aligns better.  It wasn't resting on the banking pin.
  3. I thinned the foot spring on the detent quite a bit.  It's quite delicate, but maybe I can file it thinner if need be.

Although I still can't get it to run by applying weight to the drive wheel, I was able to jury-rig a way to drive the center wheel directly.  I ran a cord over the drive wheel barrel (drive wheel removed) and attached the cord to a tooth on the center wheel, so the force was tangential.  With 3 lb of weight, the clock ran! Of course, 3 lb is too much... the drive wheel would need 30 lb or so.

Additionally, every so often, the escape wheel appears to foul on the impulse roller.  I think the escape wheel tooth strikes the top of the impulse pallet, but it happens very quickly and is hard to see.  I suspect one of the teeth is slightly (less than 0.5mm) ahead of where it should be, but I haven't checked.  It might be possible to file the tooth (or the impulse pallet) back slightly to fix this.

Clock 3 first tick

Yesterday was busy! I got clock 3 to the point where the escapement runs, but the clock doesn't yet sustain more than two ticks at a time... More debugging to come.

I started by putting a brass steady pin in the shelf to engage the center cock.

Here's the cock installed.

The clock is to be mounted on the wall, and I just learned about French cleats.  That seemed a pretty cool way to mount the clock! I took a piece of pine and planed a 45 degree bevel, and mounted it level on the wall.

The matching cleats for the clock were similarly planed from oak...

... drilled ...

and mounted on the clock.

The drive wheel rides on two-piece arbor I built yesterday, but I had to wait for the polyurethane to dry on the barrel.  The arbor was pushed into the barrel in the vice.

After that, I cut a click spring from a thin piece of oak and superglued it into place.

The center arbor was next.  Here was the planned construction.
One notable features is that even though the hour finger is to run with the center wheel, it is not directly connected.  The center wheel is held on with tight friction, but can still slip on the arbor.  The hour finger cannot slip.  This allows the hands to be set by turning minute hand -- rigidly attached to the center arbor, which turns the hour finger, and thus sets the hours synchronously while the train slips.

After cutting, I tried the fit in the frame.  This required broaching the cock pivot hole to fit, and quite a bit of sanding on the foot of the cock to get the holes into alignment.  Evidently my original drilling wasn't square...  But in the end, I got it to fit and run smoothly.

The hour finger is fit onto a squared portion of the center arbor, which I held on with a washer on the other side.  The washer was attached with Loctite 603.  I'll worry about the hour rack later.

The other arbors are screwed into the back plate.  I found that oak can be tapped for 6-32 threads if a 7/64" hole is drilled first.

The brass arbors are turned to 1/8" and threaded with 6-32 threads to a length of 3/8".

The train runs more smoothly than and I've made before, so that's a nice payoff for the large investment of time I made on getting the wheels sanded perfectly.

Now for the detent.  The locking pallet was turned, pressed into place, and then the locking face was filed.  All of this was done on the lathe to ensure a good grip.

I decided to make the foot spring from the detent itself by thinning the wood.  The foot is then screwed onto the detent cock.  Here are two views of the detent in place.

The detent also needs an unlocking spring.  This was cut from a segment of a spring taken from a broken toy car.

The hole for the spring was punched...

... and a mounting pin turned to fit.

The pin was then staked in place.

Here's the detent installed.  It seems to require close installation tolerance to run.

Now, as for running, the escapement will unlock properly, though it takes a bit of tuning.  It is also quite loud... far louder than even I would like for a long-running clock.  Even though the clock is quite handsome, if it works, it will probably stay out of living spaces...  Sadly, that's less motivation to finish the motion work...

It seems that the balance looses energy too quickly to actually work.  There are apparently a few issues:
  1. Since the foot spring on the detent is stiff, the unlocking takes a good deal more energy than expected.  Most books I've read on the subject seem to largely neglect the foot spring energy altogether.  The fact that I can't points to a design problem.  The balance could be too light -- therefore the unlocking represents a larger fraction of the balance's kinetic energy -- or the spring could be too stiff.
  2. Even without the influence of the escapement, the balance slows to a stop quickly.  This also points to loosing too much energy.  However, making a heavier balance does not fix this problem, and probably makes it worse.
I could get the clock to run consistently by manually applying force to the fourth wheel, but not to the center or drive wheels.  I found that taping small weights (in about 1/12 ounce increments, from pinewood derby cars) to the wheel helped getting the balance to have enough energy to unlock.  Even then, the oscillations quickly died out even with a frightfully large drive weight (7.6 lb) on the drive wheel.  I am definitely unhappy with that much weight, given the delicacy of the movement. 

Friday, March 17, 2017

Clock 3 frame and arbors

The frame for clock 3 is intended to be unobtrusive.  It supports the arbors on which most of the wheels spin, except for the center wheel which is supported between two pivots.  I depthed the wheels with the depthing tool and marked their centers directly on the piece of oak that is to become the frame.

I decided to recess the frame like a watch, so that the different wheels are set into the frame to result in a thinner movement.  This ought to keep the center of gravity closer to the wall.  I cut the recesses freehand using a router before cutting the frame.  Although this worked, it wasn't as precise as if I milled it.

After cutting the recesses, I cut the frame out. 

Once cut, I tried the wheels in (no arbors) to fit.  Here are two views.

The detent and the center wheel are supported on two separated cocks attached onto a shelf that mates with the back frame.

The detent cock is set on a threaded rod with a knurled knob that should allow some measure of adjustment once it's installed.
The shelf is supported both by the back frame and two shelf brackets.

Here is the shelf and the wheels, testing for clearance.

The chapter ring is for the minutes only, while the hours are read from a flag attached to the center cock.  Here they are both planned out. 

Both are marked by holes: small holes for the minutes, larger five minute holes.

The hours are marked in binary.

Here are the frame and non-moving parts of the clock being polyurethaned...

The center cock has a steady pin to aid in proper alignment.

The driver arbor consists of two pieces: an inner rod and an outer sleeve with a hole cross-drilled to engage the winding key.

The other arbors are threaded rods, backed with washers to give wheels clearance from the frame.

Tuesday, March 14, 2017

Moving a wooden clock

Motivated by an oncoming winter storm -- the clock was blocking our generator -- I decided to move Clock #1 upstairs to our dining room.  I had heard of various troubles with moving wooden clocks, so I was ready to spend at least a little time adjusting things.  The clock ran for a few hours before becoming very temperamental.  I figured that either the humidity (drier) or the temperature (warmer) of the upstairs as opposed to the clock's previous home in the basement was to blame.  So I set about trying to figure out what changed.  Although I didn't know it, neither humidity nor temperature appear to be at fault.  Since I spent the better part of the day at this task, I figured I ought to record the eventual cause for posterity.

Long story short: the escape wheel arbor is a bit too short, and so it doesn't seat fully in both bushings.  It tends to sit in either the front or the back bushing.  If the clock is set slightly tipped forward (as it was in the basement, since the floor is not level), then it sits in the front bushing.  This keeps everything aligned and all is well; the clock runs.  This is especially important because the escape wheel pinion is not perfectly cut.  If the escape arbor sits in the back bushing, the escape pinion wanders around and infrequently fouls on the previous wheel in the train.  Worse, it only partially fouls, and so steals just enough energy to cause the clock to stop with the escape wheel in some other, later position.  This was quite maddening as there appeared to be no obvious pattern to where the train stopped!

So... when the clock was first installed (perfectly level), the arbor was evidently seated in the front pivot.  But since gravity was uncertain, the arbor eventually drifted to the back pivot, resulting in a stopped clock with no obvious cause.  It was only after I had retraced everything and realized that the clock was not level when it was happily running in the basement.

Monday, March 6, 2017

Clock #3 next steps

Just a brief note about the next steps for Clock #3:
  1. Coarsely plant the wheels (on paper) to get an idea of the size of the back plate
  2. Roughly design the hands and chapter ring.
  3. Design the mounting shelf to fit the rough back plate design.  Do not forget room for (a) the hands, (b) the chapter ring, (c) the drive weight and cord, (d) the rack counterweight, and (e) the side brackets.
  4. Cut the shelf and brackets
  5. Cut the back plate and mount it to the shelf.  Do not cut recesses for the wheels yet!
  6. Design and cut all cocks.  I expect two cocks: (a) center wheel and (b) detent.  But the (c) winding arbor might need one as well.
  7. Cut the chapter ring and the two hands.
  8. With the cocks mounted, drill the center wheel arbor pivot
  9. Plant the wheels on the back plate in their final positions, starting from the center pivot hole.
  10. Recess the back plate and any cocks.
  11. Plant the arbors.
  12. Assemble!

Sunday, March 5, 2017

Drilling and sanding

The next logical step in the clock is to drill holes for all the arbors and the like.  For large-ish wheels, they can be comfortably held in the lathe chuck, like so.

For the pinions, I was concerned both with getting a hole that was truly axial and with not damaging the pinion leaves.  I remembered (somewhere) reading about cutting a recess in a wax chuck to receive the outer diameter of a wheel.  Once cut, the wheel would be set into this recess and the center could be drilled correctly with certainty.  This seemed like a good idea, so I chucked a piece of scrap pine in the lathe chuck and bored a recess to receive each pinion.  I made sure that the recess wasn't too deep, so that I would be able to grip the pinion with my fingers to remove it.  I cut aggressively with the boring tool first, and then when I got close, cut in 0.0025" increments until a snug fit.  Here is one pinion fit into the recess.

Here is another view as drilling is in progress.  I gave myself practice striking centers with the graver, which was much more efficient than using a center drill.

I used three drills, starting from 1/16" to 1/8" to ensure that I didn't have much tearout from any pinion or wheel.

The resulting pinion holes were indeed dead on center.  Since the arbors are 1/8" exactly, I broached the holes slightly larger to give a smooth, low-friction fit.

Emboldened by my success, I used a wobble stick and lathe faceplate to drill the precise holes on the escapement detent and hour rack.  This turned out to be less harrowing than drilling by hand, and ensured that no parts got damaged!

After this, I sanded off the paper, using grits up to 320 and removed the dust with a rag dampened with mineral spirits.  I think I really only needed to go to 220, though.

Trying all the parts on the depthing tool indicated that the gears run very smoothly.  All the time I spent sanding paid off!  But the hour rack had a design flaw.  The teeth of the ratchet pinion (right) foul on the rack teeth (left).

So to fix this, I cut and sanded the hour rack teeth to allow the pinion to run smoothly, which wasn't too hard.