Friday, February 26, 2010

Fun in the sun-dials

I never know where my reading will take me. I am re-reading Lybian Sands, a book by Brigadier R.A. Bagnold, OBE who was also a Fellow of the Royal Society and author of just about the only book on sand dunes that there is: The Physics of Blown Sand and Desert Dunes, reprinted (fortunately) by Dover and easily available. Also be warned that it is very technical. Bagnold was a sapper, as the British say; a military engineer. He was bitten by the bug of desert exploration by automobile in the 1920s-1930s. In the process he invented (or reinvented) the sun compass, a device that substitutes for a magnetic compass, which is of little use in a steel automobile. There are all kinds of branches to this story, but my first thought was "oooh, I gotta build one!" It is, after all, a 360 degree protractor with a big needle in the middle. Yes, but the sun's azimuth changes during the day. so you have to adjust for that. And so I came to sundials (pushed, I may add, by an article in my favorite magazine, Model Engineer, which you may Google).

Sundials are fascinating beasts. For a long time, they were the poor (and middle class) man's only way of telling time. I have found a lot of information on the web. Not all (if any) of it is correct and complete. A lot of it is "buy our sundial" or "download our unchecked software and print out a sundial" type stuff. There are two sites which are commendable: one in the UK, the British Sundial Society,
and the other a NASA link. Now a sundial is just a disk or square with marks on it to tell you what time the sun thinks it is, so where do you put the marks?

Unfortunately, there is complete disagreement by these authorities on how you mark up a simple horizontal sundial. I have now made several sundials; they are not exactly difficult:
You could make them out of plastic, cardboard, or almost anything. Almost needless to say, I made them out of wood. The one on the left is called an equatorial sundial. when properly oriented, its axis should be parallel to the polar axis. This was inspired by the British Sundial (BSS) people. The way their project is stated, it won't work unless the rectangle is transparent. Very hard to find transparent wood, so I had to reverse it a lot. The net of it is that when the pointer is exactly facing true south, it will show solar time. There is no question about the marks: one hour is 15 degrees protractor-wise.

The other dials are all horizontal. They differ in the markings, which correspond to the various authorities. I think the authorities all all wrong. I happen to have a copy of Astronomical Algorithms, by Jan Meeus, unfortunately out of print but available used. Tomorrow's project is to make a sundial per Meeus. By the way, the little triangular piece, called a stylus by Meeus and a style by others, needs to be in proportion to the sundial. The equatorial sundial is about 14 cm across; the others are pieces of a branch and about 6 cm across.

I have found out a great deal about sundials in this week. All this will come in very handy when I build a real sun compass!

Sunday, February 21, 2010

Placemat's progress

When we last saw the Navajo placemat, it looked something like this:
This was some time ago. I could consult my own posts, but I won't. So many windows on the screen, so much chance for confusion! In this image, I have done tapestry ovals, stripes, triangles, and more stripes. If we skip ahead a whole lot of weeks -- about three, I would say, we come to a more advanced stage:
As you can see, I have added a rhomboidal (double triangle) design in the center, more triangles, and some more stripes symmetrical with the bottom. If you look at color they are antisymetrical, but shapewise they are symmetrical. I am more or less making this up as I go; I made a sketch of what I wanted and then followed it -- up to a point. My objective was to master (1) dovetails, where horizontal colors overlap; and (2) lazy lines, where colors overlap at an angle. In the picture above, I am putting in a little tapestry oval in green in the unwoven warpage. This brings us to right now:

All the tapestry ovals are done, and I am doing the black fill above. The black will continue to the top. There are about 10cm left to go. Notice how the fill makes waves above the ovals. It will all have to be leveled out. We are now in what I call the end game phase of the weaving. The threads are converging to a point at the top, and it is very hard to make the heddle shed. In fact, it is impossible. So I have removed the heddle stick, and make the heddle shed with a batten (or baton). Time-consuming, but no alternative. The "stick shed" can still be made, by aid of a chinese chopstick which replaces the normal "stick." Soon the chopstick will go, and it will be blunt needle all the rest of the way. In and out. This is the Navajo way, and it is why their rugs cost so much. It is Labor Intensive (with capital letters).

I am very pleased with this placemat. It has lots of mistakes, but not so many as my first; I now know how to make dovetails and lazy lines. More when the mat is complete.

Monday, February 15, 2010

A chinook, and a trip on snowshoes

This morning we had a chinook. This is a warm wind from the south. When I woke up (at 4AM) the temperature was -7C, but by 8 it was +2.7. The snow was blown off the trees; I suspected skiing would be bad, and so it was. I managed my warmups, but when I turned on to a trail the dreaded snowball ski phenomenon took over. When it is wet, the snow forms a ball under your instep, making it impossible to go anywhere, so I gave up. One can cure this problem with fancy waxes -- klister, for instance -- but (a) I haven't any and (b) klister is very difficult to remove, and very messy. Aptly, klyster is the swedish word for glue.

However, in the afternoon I decided to see how difficult it might be to cut firewood in the dead of winter. So I loaded the sled with my beautiful japanese log saw -- a present from my offspring -- and strapped on my snowshoes (same provenance), and off I went. I had my victim marked, a downed tree obstructing my skiing. It paid for its impertinence.
Snowshoes are a very different kettle of fish from skis, far greater effort, especially in deep snow. The great advantage is that you can stamp out a platform under your tree, and be stable when you saw. Above, you can see the sled, the saw, the logs, the snowshoes, and a ski pole I use as a stabilizer. Dragging this lot back home -- a matter of 300 meters -- was a workout and a half. The sled snags in the brush, your footing is not certain, going around curves is a production. But I did it. The log saw is a marvel. I could have taken a chain saw but I wanted to see how the hand saw performed.

Notes to self: next time, make a case for the saw, and take along a japanese sawbuck. It is hard enough moving around on snowshoes; having to hold logs by hand is an ordeal.

Monday, February 8, 2010

The return of the Navajo loom

Most of my troubles with the Navajo loom -- several posts ago -- were due to improper warping. The warp frame kept collapsing, turning from a square into a rhomboid. So it was time to do something about it, and as Darth Spader would say, behold warp frame 1.0:
Nothing very complicated. Some scrap 2x4 and four sticks. Two sticks go through holes drilled into the frame and are held by wedges; the other two sticks are screwed in. They will eventually get unscrewed. This frame is solid. I put marks at 5mm intervals so I can get the spacing correctly. Right now I am using a 5mm interval; eventually I will experiment with other spacings. So let's warp it up.
I am using thrift store yarn -- perhaps the waving gods know of its composition but I have no idea. The warp on a Navajo loom takes a lot of strain; but I couldn't break this yarn, try as I might. The warp, as I might of remarked before, is wound in a figure 8 around the horizontals. The two sticks "preserve the lease" -- keep your figure 8 in the middle of the frame. It is now time to do the warp spacers. This is a distinctive feature of Navajo weaving, and keeps the warp spacing constant. There are four twisted yarns, retwisted about the warp threads.
Now we sew the tension bars onto the warp frame bars with a big needle and some strong cord, going through the warp spacers We add double cords on each side, which are the traditional Navaho side selvedges (long edges, in plainspeak) and transfer the whole works over to the loom frame.
I have also tied the heddle stick, the crooked white stick that pulls out alternate threads to make a shed. There is no reason for it to be crooked, it's what I had on hand. We are ready to weave.
There are red and green blobs in a black background. These are supposed to be tapestry ovals, but hey, I'm learning. Unlike R.M. Meluch, who I cited elsewhere, I have no Navajo spirit weaver as a guide. I call them turtles. The sword-like object in the lower foreground is a batten (I prefer R.M.'s term baton, but as a matter of fact, "batten" is indeed derived from baton, so that's OK). You can also see a shuttle in the foreground. And a bottle of Chilean wine in the background. A great temptation when weaving, which is a constant battle with topology, gets difficult. So far I have resisted it. You can also see how the warp spacers are sewed to the tension bars.

More to come as this project evolves.