Monday, December 31, 2018

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.

Friday, December 21, 2018

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.

Wednesday, December 19, 2018

Clock 4 mounting and clicks

Unlike Clocks 1 and 3, but like Clock 2, I plan to make Clock 4 wall mounted.

My wall mounting plans are to use a French cleat, since this makes it easy to remove the clock, and it's sturdy.  I attached a cleat to the back of the clock...

... but it was unstable since the plate is wide and the pendulum is off center.  So to stabilize, I added a small dowel to the back of the plate that grips the bottom of the cleat on the wall.

This means that I'm confined to use a particular size cleat (on the wall), but other dowel locations can be added easily.

The other thing I wanted was for the clicks and click springs to be carved from a single piece of wood.  I tried this on Clock 3 with oak springs, but they were very stiff and eventually broke.  Now I'm trying a pair of walnut springs, each a little lighter than the single oak I used previously. 

They're glued to the drive wheel.  I thought about offsetting them, which would lead to smoother winding, but I had trouble keeping the mechanism stable while setting up the glue. Hopefully they'll stand up to use.

Sunday, December 16, 2018

Clock 4 drive assembly

Previously, I haven't made key-wound mechanisms, so Clock 4 is to be driven by a roughly 1" barrel wound with a key.  The drive wheel rides loosely on the barrel arbor, which is (at least for now) friction-locked onto the barrel. 

The barrel arbor has a 1/8" plain pivot that fits a hole in the back plate.  To engage the key, there is a cross drilling for a steel pin.  The drive wheel is supported in a cock screwed onto the back plate.

The drive wheel meshes with a pinion that directly drives the escape wheel. 

The pinion rides on a small arbor that itself screws into the back plate.

I will cut away some of the cock to allow clearance for the escape wheel, which also will carry the minute hand (directly).  I also plan to try Aaron Dodd Crane's daisy wheel motion work to drive the hour hand coaxially.

Saturday, December 8, 2018

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).

Tuesday, March 20, 2018

Metronome flasher

Here is a circuit Edwin built this morning.  It's not complicated, but it is clever...

He figured out that the metal mechanical parts of the metronome are all in contact with one another.  He attached a wire to the winding knob, which was therefore attached to the pendulum.  By aligning the pendulum carefully with a snap circuits wire, the metronome intermittently completes the circuit.

Here is a video of it in action!

Sunday, March 4, 2018

Fly for small tent (part 2)

Based on a guy line test fit, guying at the corners is mostly sufficient.

However, the long sides have a tendency to touch the side of the tent.  Adding guys at the middle of each of the long sides seems to resolve this issue.  The only subtlety is the door; the guy line should attach to the left side of the door zipper (when facing the tent) since I'm right-handed.

Parts needed
  • 6 stakes
  • 6 guy lines each about 2 feet long
  • 4 corner attachments
  • 2 side attachments for the long sides
  • zipper pull
The top of the tent -- where all the seams come together -- is something of a mess.  To fix that, I sewed a rectangular patch at the top.

The six guy point attachments are made from siezed loops of 1/8" braided nylon cord.

These loops are sewn directly into the corners...

... the middle of the back ...

... and the left side of the zipper.

The zipper pull is a bit short, so I added a lanyard.  The lanyard starts as 2 feet of 1/8" nylon cord.

Here is the completed lanyard, which is tied directly onto the zipper pull.

Finally, I added guy lines and set the tent up.  Once up, I sealed the seams!

Sunday, February 18, 2018

Fly for a small tent (parrt 1)

We have two small, inexpensive tents that we purchased years ago.  They're simple and easy to set up.  Best of all, they're very lightweight.

But sadly, the rain fly is way too small.  Since it seems that no really suitable tents are on the market, I set about making a replacement fly.

Based on some quick measurements of the tent, the basic idea is that there are four panels.  The front panel is split with a zipper.

The panels lay out on about 6 yards of fabric on a 60" wide roll.

Here's the bill of materials:
  • 6 yd of ripstop waterproof nylon.  I'm using 1.1 oz weight, which should lead to about a total of 7 oz.
  • 3 foot zipper
  • seam sealer
  • 4 peg tiedowns

First, I chalked out all of the pieces on the fabric to make sure that everything fit nicely.
The front panel (with the zipper) is handled first so that I can compensate for any issues with the front panel size.  The zipper seam is a little complicated.

I figure that if the overlap (v above) is more than three times the zipper half width (z above), it will be fit nicely.  This means that the seam allowance ought to be about 2 v + 1.5 z.  For my zipper, this was around 5 inches.

Here are the two panels to be zipped together.

Forming the pocket for the zipper.

Sewing the zipper into its pocket.

Completed seam.

The pocket folds over the zipper and is sewn in place.

Duplicated on the back as well.

The zipper doesn't open all the way to the top, so the front and back pockets are pinned together to close the front panels together.

Completed zipper pocket.

Since ripstop nylon is slippery stuff, each of the main seams is sewn in two steps.  (I was trying this seam as an alternative to the usual felled seam.  I did three of the main seams as below, and the last as a felled seam.  The felled seam was much easier, but perhaps wasn't as well aligned.)

First, the fabric is pinned...  (use lots of pins!  the fabric is quite prone to sliding!)

... stay-stitched flat...

... then folded, re-pinned, and final stitched.

Here is the tent with the fly at this point. 

The fly is a bit floppy, but this is not surprising.  Shaping still needs to be done, and guying is critical. The attachment points for the guys are determined experimentally with the tent pitched.

Still to come:
  • Guy lines
  • Stitch the bottom edge
  • Shape the top
  • Clean up loose thread ends
  • Seal the seams
  • Add a nice zipper pull