Mini Tetrahedral Tensegrity Table Details #3: Pyramid Templates and Jigs

216
0
 Before starting to cut the pyramid segments, I cut/built some templates from the second half of the maple board I resawed and planed for the pyramid segment stock.

The first template was for the base segments. It's just a triangle with beveled sides that fits inside the pyramid's base (or sides).

With the saw blade angled 19.5 degrees, I made three cuts with my miter gauge set to 30 degrees. The only slightly tricky part was moving the miter gauge to the opposite side of the blade and reversing the angle for the last cut so the bevel sloped the correct way.







I verified the dimensions of the template by placing it on a 1:1 scale printout of the template from the SketchUp model.



The template for the side segments is a right triangle with square edges (no bevels). Again, I verified its size with a 1:1 scale printout.



Now I was almost ready to start cutting segments, starting with the sides. But I had to address an issue I had been deferring. To cut the ends of the segments at the correct angles with the saw blade vertical, I needed to run the strips through the saw at the correct orientation (balanced on their sides, on a beveled edge). This probably doesn't make sense, but the pictures below should clarify.

I considered cutting an V-groove along the long edge of the template, but I thought the strip would still rotate. After much thought, I decided to turn the simple triangle template into a cradle that would support the strip for the cut.

To make that cradle, I had to bevel two strips of the maple stock at 70.5 degrees, and to do that, I had to set the blade back to 19.5 degrees and cut the piece vertically. I didn't take photos of this step, but this photo from another project shows how I did it.





Gluing those two strips together created a holder with a V-shaped pocket that keeps the segment stock at the correct angle.



I glued that holder to the template triangle, positioning it so the knife edge of the segment stock was aligned with the edge of the template.



Then I had to trim the ends of the holder flush with the triangle. That was easy to do with a sled I built awhile back for my Microjig MatchFit dovetail clamps. It's based on Microjig's 3-in-1 tall fence/jointing sled/taper jig . (I added runner to the bottom.)

First, I trimmed the top.



Then I trimmed the bottom.



Here's the completed template/cradle.





With the templates built, I was finally ready to cut the actual segments.