First Net Tent Project

Nicholas,

I think most would draw the triangle on paper or plastic, full sized or to scale and then draw parallel lines 1” out.

If you are familiar with Pythagorean’s theorem and basic trigonometry, and had a right angle to base it on, you could figure the length of the new parallel lines mathematically.

Because you don’t have a right angle to start with, you can use the law of cosines to figure the angles you do have, and then fall back on Pythagoreans theorem and basic trig to figure what you're after.

Here’s how to calculate the first angle.

Rearrange the numbers to calculate the second angle. The third will be 180 minus the first two. It will then take a lot of steps using trigonometry to arrive at the three new corners.

A computer aided design program like Sketchup should allow you to draw parallel lines and measure between the intersections of the new lines.

Probably easiest to just draw a pattern and add parallel lines 1" out.

Hope this helps.

As Lance says, I'd just draw the panel you want, and then measure a 1" seam allowance parallel to the outline, and draw the larger outline.

If you enter the triangle in SketchUp, you can use the Offset tool to add a 1" offset to your panel. It will also tell you the length of each side, and the area of the triangle… (right click: 'entity info')

Or you can do it analytically, starting with the Cosine rule:

a^2 = b^2 + c^2 – 2b.c. cos(A)

Lance didn't call it that, or express it formally, but that's what he used… As he says, there's a lot of tedious mucking about to construct the corners

Nicholas,

If you want to pursue the analytical route, I can send you a spreadsheet which does the calculations. PM me with your email address if you'd like a copy.

Here's what the spreadsheet looks like:

Wondering why you started with the sides of the triangle, creating a trig problem to find the base and height; rather than with the base and height, which would create a geometry problem to find the lengths of the sides.

Mine was more of a cerebral journey beginning with the problem of reconciling the high cost of lightweight tents with my own limited usage potential. I thought that surely it would be a mind expanding exercise to see what shape I could come up with applying three general needs:

If I could not find a double walled tent system that was less than 3 lbs, less than $200, and gave me over 25 ft2 of interior space without requiring shock cord poles or tying it to trees ( not permitted at Philmont), surely I could achieve those parameters designing and constructing it myself.

I knew i wanted to go with a dual trek pole core, so I started there. I knew i wanted to use paracord for the structural reinforcements as well as support structure for the panels, so I started with those elements, which then define the sides of each panel. Thats how I arrived where I am now. I am sure that there are more efficient ways of doing this, but with my limited math and design aptitude, I am relying upon my artistic design skills to guide me :)

Nicholas

I see Lance has done it again… (nice).

Which got me looking at the sketch I abandoned on Friday. And, looking again, the trig isn't that tedious; drawing the seam allowance around the original triangle, and drawing perpendicular lines from the lines forming each corner to each of the seam allowance outlines, it all becomes clear…

It turns out that, at each corner, the two lines forming the corner are extended by the same amount, which is SA*(1/tan(theta)+1/sin(theta)), where SA is the required seam allowance, and theta is the internal angle of the corner.