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.

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.

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!

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.

Scroll saw throat plate

Part of my scroll saw workflow has been to cut wide of the lines and then spend time sanding or filing, because of tearout.  Also, small pinions and the like tended to fall through the throat plate, necessitating hand tools...

I read that a simple solution to this problem is to make a new throat plate for the saw, so that there is only a little hole for the blade.  Once done, it's almost like a new saw!  I could cut much more precisely -- the blade doesn't tend to drift and the tearout is much reduced.  I cut a whole bunch of parts for the chronometer clock...

Clock #3, with a chronometer escapement

The next clock design is progressing!

I wanted this clock to have a chronometer escapement, but I also wanted to rework my design workflow a bit.  Previously, I drew plans in Inkscape, which is straightforward, but doesn't easily manage complex designs.  Additionally, the only gears Inkscape comes with are involute, which I didn't want.  So for the timer, I used an online tool to make epicycloid gears, save them as a DXF and import that into Inkscape.  I thought about scripting something in Inkscape to do this better, but found that awkward.

So instead, I turned to OpenSCAD, which claims to be a "programmer's solid modeler".  This is pretty handy as I can develop libraries for later use and re-use, parameterize everything so that changes are easier (and mostly automated), and I can cut/explode/examine every part of my model without too much effort.

So to start, I wrote a library that builds gears according the British Standard 978 Part 2, taken from tables from the back of "Wheel and Pinion Cutting in Horology".  Note: I had to make use of some additional calculations from Swiss standard NIHS 20-10 in order to get some of the curves to match up properly, the description in BS 978 is slightly underspecified!  Now, I can have consistent gear profiles throughout the design.

I then spent the next few months (starting in May 2016) designing a clock movement, working sporadically.  After getting the chronometer detent and escape wheel pitched correctly -- animations were very helpful -- I got the rest of the movement in order.  I'll design the frame later, probably using the new depthing tool I made for the purpose to pitch the wheels.

The train is intended to be mounted on the wall or in standing case, and is weight driven.  It is built as follows:

• Balance wheel period: 4 s (yes, slow, but that would be kind of mesmerizing...)
• Escape wheel: 15 teeth and advances one tooth each period
• Escape pinion: 8 teeth
• Fourth wheel: 48 teeth
• Fourth pinion: 7 teeth
• Center wheel: 70 teeth
• Center pinion: 8 teeth
• Drive wheel: 80 teeth
• Drive pulley: 2 in diameter

Based on this, the clock should run about 4 days with 60 inches of cable.

As you probably can see in the diagram, I decided to try for a non-standard motion work.  It appears in Daniels' "Watchmaking" on page 173 (not an obvious location, at least for me), and also here, where the author notes that Daniels is a but uncharacteristically thin on details.  Indeed, I agree!  I had to do some side calculations to figure out how to pitch each of the components.  Fortunately, those calculations are now enshrined in my OpenSCAD model, so I don't have to worry about them again, even if I change something!

Now, on to building. The first task was to convince OpenSCAD that I wanted flat plans, not a solid model.  I guess a solid model would be better for 3d printing, which seems like a good idea for later, but I want this clock made from wood!  Fortunately, it was an easy matter to explode the parts all onto the xy-plane and cut them all through.  OpenSCAD exports to DXF, which I did, and then imported that into LibreCAD.  From there, I separated out the different parts into named blocks, and printed them all out onto paper.

My previous clocks have been built from 1/2" birch plywood, which is nice and solid.  However, it feels too heavy, especially for something so dignified as a chronometer, so I am trying 1/8" birch plywood.  Surely this cuts much more quickly, but it is also much more delicate.

I'm also trying a different workflow on the saw.  I am rough cutting the wheels with a 34 tpi spiral blade, and then using a scroll sander to do close-in sanding.   It's not fast by any means (the 80 tooth drive wheel above is only partly finished!), but it seems to give accurate work.  At least, it seems to be much more accurate than my previous work, which required many hours afterward with a file.  This clock will probably get its share of filing as well...  Lots of people have mentioned scroll sanders as existing, but since I don't have a fine belt sander it's quite nice.  I also am doing the work under a 2.5x magnifier and a bright light, so that helps too.

For later reference, it looks like I can cut wheels whose teeth have module 2.0 on the scroll saw.  Anything smaller is too fine!  Fortunately my OpenSCAD model is parametric in the module...

New clock depthing tool

Picture says most of it.. I designed a new depthing tool in OpenSCAD that should be a bit more stable than the previous one.  It's also intended that the arbors are fixed and the wheels spin around them.  The design consists of two parallel bars that hold three I-shaped blocks.  The outer two I-shaped blocks are attached to the bars, while the middle one can slide.  The left two blocks have arbors through them.  The sliding block is locked by tightening a knurled nut holding everything together.