Sunday, December 31, 2017

My "usual" pants hem

I almost always wear "formal" pants, since I don't find jeans comfortable.  Since I'm short, I usually have to hem my pants.  While a simple "straight" hem is functional, it is not quite as sturdy as I need for every day usage.  The visible seam isn't quite as nice, also.

Since I had to re-hem a suit some years ago, I took apart a more fancy hem on the pants and developed my own technique.  Ironing is crucial.  I set the iron on its maximum temperature, since I'm setting creases rather than merely taking out wrinkles.  Depending on the fabric, this requires some caution so that the fabric isn't damaged.  Since I prefer wool over other materials, this is rarely a problem, but wool-synthetic blends require a more light touch with the iron to set a crease.

Here is now what I usually do... 

My inseam is 25", so everything is referenced off of that.  I start by cutting the pants to somewhere between 28 1/2" and 29" (inseam plus 4"). 

Then I fold this in to 28" (inseam plus 3") and iron.  (I don't turn the pants inside-out, so the picture below is of the outside of the pants along the inseam.  The extra fabric you see from 28" to 28 1/4" is the inside of the other side of the same pant leg.)

I machine stitch this edge.  Thread color does not matter, since it will be hidden.

I bury the bitter ends of the thread on the inside of the seam, so they can't catch on anything.

Then I iron another crease, now at 26" (inseam plus 1").

And before any further stitching, I fold and iron at 25" (the final inseam).  This almost always requires several passes of the iron since there are many layers of fabric to crease.

At this point, the hem needs to be anchored with a stitch.  But since I don't want the thread to show through the outer layer, I don't stitch this with the machine.  So I hand stitch through all layers but the outer layer.

Here is the view from the inside of the pants...

... you can see no thread on the outside ...

... the stitching holds together here.

Here is the finished product.

Thursday, December 28, 2017

Transistor oscillator

I have been looking for a simple, easy to understand oscillator circuit that uses a single transistor.  Well, I found one!  Twice, it seems.  The first place was in a classic vacuum tube circuit, as described in

Morecroft, Elements of Radio Communication, Wiley, 1929.

After suitable edits to make it transistorized, I then found the same circuit in a hand-drawn schematic that my father had squirreled away in the 1944 edition of the ARRL Handbook. Certainly not new!

For my and Edwin's benefit, I built the circuit using snap circuits.

Here's the schematic:

The different parts of the circuit are indeed easy to understand:
  • The tank resonator is an inductor-capacitor (LC) circuit, which sets the frequency.
  • The keying turns on and off the oscillator.
  • The bias ensures that the transistor is turned "on" and not saturated.
  • The transformer affords feedback from the tank to the input of the transistor.  It also contains the inductor part of the tank.  In the snap circuits version, we don't have much control over this (it's in a plastic package), but too little inductance will cause the circuit to fail to oscillate.
  • The 200 ohm feedback resistor sets the gain of the transistor amplifier.  Reducing the resistance increases the gain, which drives it harder.  Increasing the resistance makes for a cleaner signal, but can also stop the oscillations. It seems to stop around 1000 ohms or so, but with the 200 ohms it is noticeably overdriven.
  • The signal purity can be increased by selecting a higher voltage for the power supply.  I got it to work with 3 volts, but the output was more clipped.

Clock 3 cased and installed

Clock 3 is finally complete, and is now installed in an oak frame/case in my office.  The case has a matching French cleat so the movement is easy to remove for debugging.  I also installed a dial that is perched on pins on the shelf, which allows it to be easily removed by lifting it off the movement. 

It is now driven by a 10 pound bag of lead pellets (intended for scuba diving) with a two-fall pulley.  It runs for 16 hours on a wind.  This short run time is well enough so that it shouldn't bother my office neighbors.  It's a bit noisy, but now that it is no longer mounted on a hollow cavity, it's quieter than before.

Moving the clock from my cool, damp basement to the warm, dry office did require some adjustments...  The movement's frame has the grain going horizontally, which meant that it shrank vertically a bit.  This caused the impulse pin to bind on two things:
1. The detent tip, which required shifting the detent back slightly
2. The trailing edge of one escape wheel tooth, which required a small amount of filing.

The great wheel also fouled on the frame -- an indication that my "fancy" milled frame wasn't a good idea -- since it appears that the frame has shrunk vertically.  To compensate, I carved the milling back further.

The great wheel pivot, which I had previously needed to move (and I wondered why!) had to be set back in its original position as well.

Additionally, many friction-fit parts loosened and required the use of super glue to anchor:
1. The impulse pin
2. The hour finger
3. The dial pins 

Loop antenna

Since HF antennas tend to be rather large, I wanted to try a small resonant loop.  After doing some research, I found a few sites that seemed rather detailed.  This one seems about the best.

I constructed mine from 3/8" copper tubing, and it is mounted on a camera tripod base.

It is fed using a gamma match.

The tuning is accomplished by a scavenged broadcast FM tuning capacitor and a homebrew air-variable butterfly capacitor.

The antenna can be tuned on the 20 meter through 10 meter bands.  Here I am using it on 20 meters...

Wooden hygrometer

Based on the issues of wood expansion with my clocks, a natural project would seem to be a wooden hygrometer.  At least, it ought to respond about as fast as the wood in the clocks responds, which appears to be around a few days. 

The design is fairly simple, with two oak sticks of roughly the same length being placed parallel to each other and rigidly anchored at one end.  One of the strips has the grain running lengthwise, while the other has the grain running perpendicular to that.  The two free ends are pinned to a needle.  I placed the parallel-grain strip on the bottom, so that the needle moves to the right as the humidity increases.  With this particular item, fully soaking it for a week in water runs the needle all the way to the right of the scale.

But the typical indoor humidity is closer to the first picture.  The needle usually moves around 1/4"-1/2" with daily variations.

Sunday, September 10, 2017

Clock 3 drive updates

Now that Clock #3's escapement seems to be working, I replaced the center pinion with a v-pulley.  I made the v-pulley from two 1/8" plywood disks in which the edges were beveled in the lathe.  I used hot glue to adhere the disks together, and used a heat gun to ensure the pulley was evenly glued.  The v-pulley was secured to the center wheel by a pin.  It seemed that this would grip an 80 lb monofilament fishing line if a counterweight was used.  The line settles into the groove for an effective radius of 0.75 inches.  The clock ran for over an hour on 3.25 lb drive and 0.5 lb counterweight, which works out to just about 2 inch points of torque on the center wheel. 

I also noticed previously that escape wheel wheel drifted up on its arbor, so I added a small wooden washer cap that press fit to the arbor.  This seemed to work well enough.

Tuesday, September 5, 2017

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...

Sunday, August 27, 2017

Clock 3 torsion pendulum Q

So the pivots on Clock #3 clearly are consuming energy... I tried the torsion pendulum outside the frame (basically just excluding the pivot).  I counted 70 periods before the amplitude halved... which yields a Q of roughly 315.  But there is considerable wobble since the balance itself is badly out of poise.  I tried to clean this up a bit on the lathe and redrill the center hole (which is misaligned).  Repositioning the suspension hanger also helped, so now the rod spins vertically without much wobble except when the impulse is given.

This seemed to help a bit, as the necessary drive torque has dropped to 1.75 inch-pounds, or about 0.34 mW.  This is about 2/3 as much power as Clock #1 uses, which gives basically one day of runtime with about the biggest weight I'm comfortable with.

Much better, but I suspect that there is still easily fixable power loss due to the wobble at impulse.  If the pendulum weight is placed lower (on a longer rod), this should be reduced, and might help matters further.

Wooden clock power consumption

For reference...

Clock #1 is powered by a 10 lb drive weight that falls 46" in 27 hours.
Power = (10 lb * 4.448222 N/lb)*(46 in*0.0254 m/in)/(27 h * 3600 s/h) = 0.5 mW

Clock #2 is powered by a 1 lb 4 oz weight that falls 11.5" in 5.5 minutes.
Power = (1.25 lb * 4.448222 N/lb)*(11.5 in*0.0254 m/in)/(5.5 min * 60 s/min) = 5 mW

Clock #3 (as it currently stands) is powered by a 4.125 inch-pound torque on the center wheel.
Power = (4.125 lb*4.448222 N/lb)*(6.28319 in/rotation * 0.0254 m/in)/3600 s/rotation = 0.8 mW

This explains why Clock #3 power consumption seems high... Torsion balances are supposed to be much more efficient (if lower Q) than pendulums, but this one is not!

Saturday, August 26, 2017

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.

Thursday, August 17, 2017

Clock 1 humidity redux

I think I have finally figured out what goes wrong with Clock 1 when the humidity changes.  After much watching and poking, I found that the third wheel appeared to be sticking slightly, at least whenever the clock stopped.  Carefully pulling the third wheel backwards once the clock stopped, I could feel some rubbing...

I think the third wheel pinion expanded a bit beyond where it was supposed to, or maybe the frame expanded, but in any event, it was fouling at the tip.  After ensuring that the pivot was rigidly planted where it was supposed to be, I took to very slightly filing the addenda of the pinion.

This makes the pinions closer to an ogive form.  I don't think this really matters, because the clock is now happily running even though the humidity has been around 60%.  Hopefully I won't run into an "opposite" problem when the humidity drops later in the year.

Monday, May 29, 2017

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.

Saturday, April 29, 2017

Clearning and reassembly of "La Duchesse"

Now that the pendulum has been replaced for "La Duchesse", it's time to clean and reassemble it.

The movement is a standard two-spring American movement with a count wheel striking mechanism.

Here's another few looks at the movement to make sure I didn't forget anything later upon reassembly!

After taking down the mainsprings (carefully held in place with wire), all of the wheels were removed and cleaned in the ultrasonic cleaner.  The plates were scrubbed with soap and water (avoiding any polishing of anything!) to get the old oil off.  At this point I noticed some interesting things: (1) there are no oil sinks to speak of, (2) there is only minor wear, most of the pivot holes pass the broach test outright, those that didn't were easily opened slightly to round, and (3) the mainsprings were apparently unlubricated.  I also took apart the mainsprings to inspect them -- they were essentially in mint condition.  Dimensions: 3/4" x 0.017" x didn't bother to measure. but they make about 9 full turns when winding

I polished all pivots by hand, using the lathe to hold everything steady.  (No power applied!)

Here are all of the parts cleaned and polished on the bench, ready for reassembly.

Movement reassembly was straightforward except that I had to take several tries to get the warning wheel in the right spot so that striking finished correctly.  Annoyingly, each try displaced all of the pivots, but it wasn't anything major.

The final repair was to fix the door hinge.  The pin was missing, so I made a replacement.  I suspect the original was brass, but I made a new one from steel.  It seems like someone had forced the door downward when it was opened, which cracked off the top hinge pipe on the dial.  I made a replacement one.  The original hinge was clearly soldered in place, but since the dial was painted with gold paint and ceramic, I didn't want to risk heating it.  So instead, I used some sturdy epoxy, which I think was reasonably unobtrusive.  I also had to re-broach the two original hinge pipes because they were warped off in a bad way.  (You can see that in the picture below to some extent.)  Even still, the door doesn't totally snap in place, but at least it closes.

And here is the assembled clock, sitting on my bench.  It's running now and just happily struck 11:00pm.  (However, I must protest Ansonia's choice of an incongruous kitchen-timer-sounding bell for this otherwise somewhat pretentious clock!) 

Monday, April 24, 2017

Replacement pendulum for "La Duchesse"

Since the pendulum on the La Duchesse clock is missing, I am attempting to replace it.  I started by threading a length of 1/8" steel rod with 6-32 threads.  That's at least a standard size for which I could either make a knurled nut or buy one.

I find it easiest to thread by hand on the lathe (with the power off).  That way everything stays neatly aligned.  There are markings on the movement saying "3 3/4", which I take to be roughly the length of the lower rod.  At least, that makes the rod just longer than appears to fit nicely in the case.  It's easier to shorten a rod in any event...

The pendulum rod is segmented.  The upper portion is attached to the suspension spring and the crutch, and is also not missing.  The lower half fits a hook on the upper half.  Judging by how the Ansonia Crystal Regulator was made, the lower rod is flattened at the top and drilled to receive the hook.  So, to that end, I heated and hammer the top of the now-threaded steel rod flat.

I center punched the flat, and tried to drill it with the appropriate size drill.  Since I was using a hand drill (I don't have a drill press, and didn't try to set up the work in the lathe... probably should have), I had trouble with the bit slipping.

So I gave up, and bent a hook in the lower half as well.  This was now easy since the steel was flat and annealed.  However, it was too wind to receive the hook in the top rod.  So I filled the hook in the lower rod to fit the upper hook nicely.

Once filed, I hardened and tempered the rod to blue.

I center drilled and turned a bob from a piece of lead (total weight around 1 oz).

I was initially concerned about turning lead being problematic, but it went nicely enough and the surface finish was good.  Since the bob will be concealed inside the case, I didn't feel a need to attempt to polish it.  Eye protection (as usual) was a must, but especially so since the chips were launched everywhere... messy clean-up.

Sunday, April 23, 2017

Dell Venue 11 pro keyboard fix

My main computer is a Dell Venue 11 pro, which I am generally happy with.  It runs Linux nicely, has an active digitizer stylus, a touch screen, and does just about everything I want.  (The only exception is that it uses micro-HDMI for display output, which is uncommon on projectors... so I can't use it to present at a conference, which is a bummer.)

It's a convertible tablet with a detachable keyboard.  There are various kinds of keyboards: (1) a desktop docking station that I use on my desk at work (I have a USB keyboard, trackball, wired ethernet, and an additional display), (2) a thin folio keyboard that is very lightweight, and (3) a heavier keyboard that also has a spare battery.  The thin keyboard is a little less nice to type on and feels delicate, but I use it when I don't want to carry extra weight.  I usually use the heavier one because typing is nicer.  It basically makes the computer into a laptop.

A few weeks ago, the computer started having issues charging the keyboard's battery.  Worse, it refused to boot at all!  It was quite badly stuck and would not even show the BIOS Dell logo...  Uh oh.

After looking around the forums, I found that the thing to do was to open up the machine, disconnect the battery and the RTC battery (marked), and

then hold the power button for a few seconds.  Upon reassembly, this procedure seemed to restore life to the machine.  Plugging the machine into its dock or the folio keyboard seemed fine, but plugging in the heavier keyboard killed it again!  Figuring that the cause was the keyboard, I ordered a replacement.

The replacement seemed OK except that the spare battery was not detected.  This is apparently a "design feature", and requires you to charge the keyboard separately first.  So I did that, and then trouble struck again...  When the keyboard battery was charged, it bricked the machine again!  Uh oh... evidently the keyboard was not the problem, even though it seemed otherwise.

More searching of forums revealed that the problem is actually that the pins on the bottom of the tablet had retracted into the case and therefore where not making good contact anymore.  The dock uses a separate connector, and is therefore unaffected, and the folio keyboard connector pins are apparently longer.  Since I had to take apart the machine again anyway, I followed the forum post's advice and removed the rest of the case to expose the pins.  This being a modern-ish computer, not only are there screws (with standard heads, thankfully) there are also many delicate-but-stiff spring clips.  I think I managed to avoid breaking them!

It was straightforward to very delicately and gently tap the pins using my staking set from the inside of the case ...

... until they slightly emerged from the bottom of the case as they should.
I reflowed the solder (using lots of flux) around the connector to make sure I hadn't accidentally broken any connections in the process.

This seems to have fixed the problem, as I am posting this using the keyboard and both batteries are indeed showing up as present!

Update (4/24/2017):
When I got to work, the desktop dock didn't work... and later the machine flaked out on the keyboard again.  Argh.  It turns out that the two ribbon cables for the daughterboard at the bottom of the case under the battery (one for the dock, labeled as such on the cable and "DOCK 41 PIN" on the board, leftmost, and the other labeled "LCM" on the cable and "DOCK 45 PIN" on the board, next to it on the right) needed to be reseated.  The cable displacement was not visible (to my unaided eyes) but was visible under a 5x loupe.  In any case, reseating both cables seemed to fix it.  Indeed, the loose ribbon cables might have been the problem all along!

More links about this problem: