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.