December 2019 archive
I'm considering making something that will include rack and pinion gears made of wood, and before cutting anything I've been reading up on gear tooth shapes.

I started (where else?) with Wikipedia, where I saw that the gear article describes an insect, Issus coleoptratus, with tiny interlocking gears to synchronize the movement of its hind legs when it jumps. This was the first instance of functioning gears discovered in an animal. Is this way cool, or what. Issus coleoptratus Also, I encountered the word dedendum, analogous to addendum—except that addendum is in common parlance and dedendum is gear jargon.
Artifacts of aerial photography as a sequence of color‑filtered exposures. Yes, I posted an example of this before—but that one didn't have a shadow. Yes, I am easily amused. Happy solstice, everyone. -12.003,-77.124
In 1893, the USA standardized the foot as 1200/3937 meter. In 1959, the foot was redefined as 0.3048 meter, a US and international standard used to this day. It differs from the 1893 definition by two parts per million.

Surveyors kept using the old definition and know it as the US survey foot. The USA is divided into 124 geographic zones, each with a map projection tailored for low distortion within the zone. Coordinates within zones are often given in feet.

US authorities have been wanting to ditch the survey foot for a while but only recently put their foot down (sorry). The survey foot will be deprecated in 2022. That's when a new datum will replace NAD83 (which gets the center of the Earth wrong by about 2.2 meter). As long as you're upsetting one applecart, might as well upset another.

The impending demise of the survey foot was in the news recently. Russian media made snarky comments along the lines of why don't you just use meters, which made me curious to see what the Russian language Wikipedia page for the metric system had to say about the USA. An excerpt (via Google translate):
...the USA is the economic and technological leader in the world, and representatives of imperial thinking believe that it is not worth the US "trendsetter" to adapt to others, even if it will bring tangible benefits. This is confirmed, for example, by the US's reluctance to switch from Letter paper format to mathematically justified aspect ratios and accepted by all other countries in the world according to ISO 216 standard.
Not all other countries. Canada, Mexico, and a few others use 8½×11" too.

Certain US standards (e.g. fractional inch measurements and tool sizes) cause me occasional frustration but it doesn't bother me that our paper has an aspect ratio other than 1:√2. It never happens that I fold a piece of paper in half and wish it stayed the same shape.

Certain products are in inch sizes worldwide, e.g. socket wrenches in ¼", ⅜", and ½" drive, and car wheel diameters in inches.
Erythrostemon gilliesii (formerly Caesalpinia gillesii) is an ornamental shrub popular in my area. It's suited to our soil and climate and has nice flowers. It exhibits impressive explosive dehiscence. A friend and I were near one of my plants when it ejected a seed hard enough to hit the roof of my house.

My favorite specimen started on its own about 20 years ago from seed thrown by an existing plant. Unfortunately it's next to a frost-free hydrant which has a drain valve about 40 cm below grade. I recently replaced the hydrant because roots had invaded the valve. I now face the question of whether I love the plant enough to accept having to continually replace the hydrant (which I use a lot).

This pic of one of the plant's flowers is from 2015. Erythrostemon gilliesii
Sylvilagus audubonii
You may well ask, why am I posting a photo of a seemingly nondescript plane? Hint:  it usually flies at night and this is the first time I've seen it by light of day. N747NA at about 39000' It's an old Boeing 747 modified to carry a big telescope. It's used for infrared astronomy observations which benefit from being way above most of the water vapor in the atmosphere.
When I first started working with wood, making curve‑shaped things usually started with drawing a shape on paper, perhaps with the aid of a compass and French curves. After settling on a shape, marking it on wood (with carbon paper or by cutting out the pattern and penciling around it) often introduced error.

I'm glad I don't have to do it that way anymore. The PostScript language (and many drawing programs) let you create cubic Bézier curves which concisely describe all kinds of shapes. You can print patterns on adhesive labels or clear film and stick that on wood before cutting.

The pic below came from some work I was doing on Thanksgiving day. I know it's traditional to give thanks for necessities like health or food or shelter but I am also grateful for Bézier curves and laser printers.
clear film pattern on maple
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