Sunday, September 20, 2015

Two weekends of clock construction

I made considerable progress on my timer over the past two weekends.  I started with a pile of parts (after sanding)...
... and ended up with a nearly complete, partially functional timepiece!
Here is how it happened...

Since the design phase, I had left the spacing between the two plates as a yet-to-be determined variable.  The key distance was the winding barrel, which had to rotate freely around the main wheel's arbor and engage with the ratchet and click assembly.  I wasn't quite sure how much room I'd need, so I built the winding barrel first.

The winding barrel is hollow, and has two transverse pins to anchor the winding ribbon.  First, I turned the outside of the winding barrel from 1/4" brass rod.  Notice the thicker end (left) to receive the ratchet wheel.
I filed flats on the narrower portions...
And drilled holes to receive the pins in the flats.
I turned the pins from 1/8" brass rod, tapered to fit into the holes.
I pressed the pins into place with the vice.
This wasn't secure enough to keep the pins in place while center drilling, so I also soldered them.
I center drilled the assembled winding barrel in the lathe.  
After it was drilled, it was fit friction-tight into the ratchet wheel.

Now that I knew the length of the winding barrel, I could estimate the distance between plates.  Here are the two standoffs that hold the plates in place.
I also fabricated four pivots and two hollow bushings for the three arbors.
Here are the main wheel pivots drilled and fit into the frame.
Once that was all in place, I turned the main wheel arbor so that the winding barrel fit around it.  I turned this out of a single piece of 1/4" brass rod, which took a while.
Then, I pressed the assembly together -- the winding barrel is permanently captive on the arbor.
With the main wheel assembled, I could align the main wheel pivot and bushing by aligning the two plates.  This ensured that the arbor was installed perpendicular to the plates; if I had assembled the plates first, there was the risk that the pivot and bushing centers might be slightly out of alignment.
Next, I started to assemble the winding mechanism.  Here is the click in place; I used a short nail with a broad head to attach the click so that it can move freely.
For the spring, I used the drive spring from a broken toy car.  (There are lots of toy cars around my house since Theodore loves cars!  Whenever a car gets destroyed, I scavenge for useful parts, springs in particular.)  The spring was easy to cut with diagonal cutters, and easy to bend to shape with tweezers.
Here is the spring installed with two small finishing nails.  I put the nails in first...
... and then trimmed off their points flush with the back of the wheel.
In order to drill the other wheels, I realized that I was struggling to get perpendicular holes since I don't have a drill press.  So, I made a clamp assembly for my lathe's flat faceplate.   I started with a sheet of steel and drilled four mounting holes.  I think that the steel was probably hardened, and I was unable to anneal it with my small propane torch.  Anyway, I broke two drill bits.  One was a carbide-tipped bit for drilling glass, which cracked -- thankfully after finishing the holes!
Then, came the job of cutting the clamps out.  Again, much tool stress later (wore out the teeth on my hacksaw and two jeweler's saw blades), I had my clamps.  I filed them neatly, so they wouldn't mark anything.
Here they are, holding the second wheel securely in place.  I also made use of a wobble stick to get the center just right.
And with that, turned a simple arbor and fitted the wheel and pinion into the frame.
Now, on to the escape wheel.  Again, it was important to get the size of the escape wheel before making its arbor.  The escape wheel consists of two three-toothed wheels, held part by three brass pins.  Here are the pins, turned from 1/8" brass rod.
The pins are pressed into holes on each of the wheels, forming the escape wheel.
Now, with the escape wheel sized, I was able to figure the length of the arbor.  I learned my lesson with the main wheel: turning down a 1/4" brass rod to 1/8" over nearly its entire length so that you have a hub takes long time.  To economize on time a bit, I turned the arbor from 1/8" rod brass, and made a separate hub from 1/4" brass rod.
These two items were soldered together, thereby avoiding waste of time and materials.
The escape pinion was pressed on, using my now-standard technique of pressing on the lathe.
As usually happens to me, the depthing for this wheel wasn't perfect.  So I opened up the bushing and pivot holes a bit and shimmed them to fit.
Here, the escapement wheel is pressed into place on its arbor.  This means that the escape wheel and its pinion are permanently attached to the outer plate.
Trial assembly; most everything seems to fit.  The wheels turn (mostly) smoothly, with the escape pinion occasionally binding.  That'll be a problem for later, but it will need to be managed...  Anyhow, this was the end of the first weekend, probably about 10 hours in total.

The second weekend started with making lots of pins...  There are (top to bottom) 2x locking pins, 2x pendulum crutch pins, 2x gravity arm pivots, and a pendulum support.
Here are the locking and crutch pins installed on the gravity arms.
Here are the gravity arm pivots.  It turned out that I had made these too short, so I put washers in as a stop-gap measure.  Will need to fix later.
The pendulum support rod was set up in the style of what's shown in Gary Mahoney's clock:

I slit my pendulum support rod with a jeweler's saw, filed two flats, and then drilled to receive a screw.
This allows the pendulum to be attached with a flexible hinge of some sort.  For the moment, I'm using paper.  Maybe I'll use a flat spring.
The whole mechanism is assembled and mounted!
It runs, somewhat intermittently, with 4lb 4oz of weight!  It is noisy!

The key issues seem to be that
  1. The escape pinion binds occasionally, stopping the clock
  2. The escape wheel occasionally skips, in which it slips past its locking pin rather than being captured.  This is kind of catastrophic since the pendulum receives an out-of-phase impulse; sometimes it can recover, sometimes it can't.  I think the cause is the gravity arms slipping along their pivots.
Remaining tasks:
  1. Cap off the ends of the gravity arm pivots.  The arms tend to slip around and off the pivots
  2. Fix the gravity arm pivots by either remaking them (preferable) or making custom washers so that they keep the gravity arms the correct distance away from the outer plate.
  3. Fix the depthing of the escape pinion
  4. Fabricate a pendulum bob.  The current bob is attached with a rubber band
  5. Replace the pendulum pivot with something a bit stiffer than paper -- the pendulum wobbles axially too much.
  6. Fashion a drive weight and winding pull
  7. Fashion a hand for the main wheel arbor
  8. Further debugging until it runs reliably

Monday, September 7, 2015

Much filing ensues

I decided that I should rough cut out parts for the timer, and the file them to their final shape.  This way, I should get finer control of the accuracy of the parts, and would avoid gouging them with the saw.

Anyhow, this is a time consuming proposition...  Many hours of filing later, I have this (almost complete) pile of parts:
The gravity arms have yet to be filed, but they're not too critical.  The cycloidal gear teeth took a long time... much longer than the involute teeth on my previous clock.  Also, I was very particular about the spokes.

I still have yet to cut the blocks that will hold the plates apart; I'm waiting until I finish assembling the drive pulley and ratchet since I'm a little unclear of how large that will be.

Sunday, September 6, 2015

Winding stem for calendar watch

I have an old Agon calendar wrist watch from my father that is missing a winding stem.  It looks like the winding stem snapped off at a critical point.  So, I set out to fabricate a replacement.  I've made four replacements thus far, and all but the last ended in failure -- breakage of the part -- but each got a little closer to success.  The replacements #2 and #3 were able to wind the watch, but not set the hands.  Replacement #4 appears to work.

Here's the original; the break is just to the left of center.

From the original, I took careful measurements for plans.  (Beware transcription errors -- I accidentally swapped two digits, which did in replacement attempt #2.)

Here is the original (bottom), the first attempt (top, and the second attempt (middle).
The orange blob on the left of the second attempt is a bit of binding wire.  I thought I had steel binding wire, but it was actually solder-coated copper.  So when I heated it for hardening, the copper melted and welded itself onto the (then already broken) part.

The pictures below chronicle the making of replacement #3.  Before going any further, I'll note that replacement #3 ended up breaking.  It also didn't have the right sized hub behind the flats, so it couldn't set the hands reliably.  I fixed that for replacement #4, but didn't take pictures.

I started by turning a 1/8" steel rod to size: 0.051" diameter, and then trimmed it to size.  After that, I turned the pivot: 0.019" diameter.

Then came the rather delicate task of trying to file the flats.  Since I don't have a filing rest (maybe I should...), I did this by hand with the absolutely finest files I have.  They're not very fine, in the end, but appear to be sufficient to get me started. Below shows a trial fit in the frame.

I finished the filing on an oilstone so that it fit the crown wheel...

Next comes the fairly delicate job of cutting the slot for the portion that grips the handsetting mechanism.  Here it is in progress...

... and here it is finished, with the original next to it.

I had a lot of trouble reaching the graver into the slot to make a smooth slot.  And, as it happens, the hub on the pivot side is too narrow to grip the handsetting mechanism.  So in replacement #4, I cut the slot deeper, with a sharper (more right-angled) slot.

At this point, I parted it off...

And hardened it in water.  (Perhaps should have used oil?)  Here it is bound in steel wire.

Anyhow, this was a lesson learned from replacement #2 -- I left it in its original (not hardened) state for trial fitting and broke it.  And replacement #3 broke after being fully hard... so for replacement #4, I polished and then carefully blued it, so hopefully it can take some stress.

Here's the part at this point...  just before final polishing.  And at least occasionally it can pull the crown wheel back for handsetting.

It's just about the right length, too.

But, I wanted to remove it to inspect the hub, and it jammed and then snapped!  So I had to try again... Replacement #4 seems like it is just about right...

Start-to-finish it took about 3 hours to make replacement #3 and 2 hours to make replacement #4.