On Sun, 6 Dec 2009 15:35:12 -0500, "Existential Angst"
wrote:

"Jim Stewart" wrote in message
...
whit3rd wrote:
On Dec 5, 12:00 pm, "Existential Angst"
wrote:
Awl --

Suppose I have a box, a 6" cube, made from 6 pcs of 1/4" alum,
butt-jointed
together.
No big problem, altho depending on the exact connections, all 6 pcs may
not
be identical.

OK, now suppose the top face is not 6x6, but, say, 1x1 (or whatever), so
that sed box is now pyramidal.

I would imagine SW would figger all the dimensions and bevels for you

No software will do this without more information; the thickness of
the
material determines the slant height after beveling, for instance.

If you have multiple plates joining, the orientation of each plate can
be made into a 'normal vector', and by dot-product of vectors
you can determine the angle of the plates' intersection. The bevel
is half that angle, of course. Use Cartesian geometry, it all
works out. Alas, one DOES need familiarity with vectors in
three dimensions, and a bit of software to do the normalizations,
dot products, cross products is ... useful. Do Fortran much?

Yawn.

Easier to draw it to scale then measure it. We're
polly not building a 787 here...

Yeah, but he's basically right, except no fortran nec, just a spreadsheet.
787 or not, it's just as easy to get it absolutely exactly right in a
spreadsheet as it is to fudge it.

But, 'til a spreadsheet or utility materializes, fudge it is, and for now,
1/4" = 1" on graph paper is proly my best bet.

This would have been an easy homework problem in descriptive geometry,
a freshman engineering course back in the day. You construct three
orthogonal views (top, plan and side). Then, using dividers and
straight edges, you construct aux views until you get a "true view" of
the bevelled joint. It's all graphical, no calculations or math.

This is how about everything was designed, including automobiles and
airplanes. The guys that did it were well paid. They often worked on
1:1 drawings, wearing kneepads and holding eyeball accuracy to 1/100
inch.

http://en.wikipedia.org/wiki/Descriptive_geometry