Re: [MedievalSawdust] 'peaked roof' boxes
- On Mon, August 10, 2009 8:03 am, Liedtke Goetz wrote:
> I'm home ill - therefore brain-dead - but I suspect there's something inA kamal is a simple navigational tool that works by sighting a distant
> classic geometry that makes possible constructed rather than carved
> peaked roof chests. My brain is trying to find the right information but
> failing....it has something to do with isosceles triangles, 30 and 60
> degree angles, and such stuff.
> I've been reading a book on navigational instruments (worth checking out
> by those on this list) and much of period navigation is based on that
> same classic geometry. I wonder if working out the angles could be done
> with something like a kamal <http://en.wikipedia.org/wiki/Kamal>?
target across a known angle. (Traditionally a wood or bone tablet with a
string running from its middle. The far end of the string has a knot in
it, arm's length away from the user. The knot is held in the observer's
teeth, so as to give a consistent "arm's length" for every sight taken.
Navigators use it to judge the height of a star above the horizon. (In
the Indian Ocean, Polaris is close enough to the horizon to measure
latitude this way.)
Kamals only work for small angles, and basically for getting angles
between two distant objects. You calibrate your kamal by sighting pairs
of known stars with it, and marking off in "esbah" units, which I
understand originally referred to finger widths--traditional navigators
all over the Indo-Pacific just extend their arm with the palm bent at
right angles toward the face and sight stars that way; the Arabs just
added standardization by marking the card against the star pairs.
This actually works for navigation--believe it or not you can get your
latitude right within thirty miles, as long as you are in low northern
latitudes and have a clear level horizon to the north.
More than you ever wanted to know about traditional navigation! But what
I can't see is how you'd find it useful close up. As I understand Baron
Conal's problem, he already has a formula for the compound angle he needs,
it's just a PITA to set up. You don't need a kamal when you already own a
protractor, and most table saws have a couple of those right on the
Mary's suggestion of kerfing between oversize pieces makes sense, and
could certainly have been done in period. A similar method from
traditional metalwork (for precision fitting) is to put chalk or charcoal
powder on one side of the joint you're fitting, press the parts together
and look for high spots. The chalk rubs off the high spots on the chalked
piece, and shows up on the high spots of the bare piece; you then take the
high spots down a little with file or scraper. Or for woodworkers,
perhaps a small plane.
Whether any of these save time over a bunch of trial cuts, questionable.
They might reduce the firewood buildup problem, though. Personally, I've
never seen why firewood buildup would be a problem, but then I've heated
with wood the last thirty years. Gives a whole new perspective on shop
> p.s. Latitude Hooks and Azimuth Rings: How to Build and Use 18
> Traditional Navigational Tools, Dennis Fisher, ISBN 0-07-021120-5 -
- I love this group. Where else can one ask about how to clean copper pots and end up making moonshine in them! A natural progression.Anne
Go softly and gently for those you meet here will be
those you know hereafter."