My reading of the first post was that the goal was for a 3 side pyramid shape.   Last fall semester I had a student who designed a little side table with an inverted 3-sided pyramid section center. Wide end up. I have a photo somewhere but it'll take half the day to search for it.  The miter angle between the sides was not 30 degrees, but was close to that. A triangular tube would have 30 degree miters between sides, but as the sides start to taper in that angle changes slightly. From a fine woodworking article: "The angle between sides, the dihedral angle, is 70.52 degrees. Half that, 35.26 (let's say 35.3) degrees would be the miter angle".

 

When cutting the side parts for the student on my CNC, I didn't have to know the angle.  She had a 3D cad drawing in Rhino, from which she was able to export a flat view of one side with both the top inside lines and the bottom outside lines.  I knew the boards were 1/2 inch thick and that the slope of the sides would simply be from the inside lines to the outside lines and .5" down.  Using a moulding toolpath in Aspire and a section view I cut her shape and they fit perfectly together. 

 

I'll post a photo of the project once I find it.

4D

 

Edited May 16, 20224 yr by 4DThinker

1 hour ago, 4DThinker said:

My reading of the first post was that the goal was for a 3 side pyramid shape. 

 

Nicely done 4D!

Thanks Cal.  The table has a CNC cut 3D model inside of a mountain area by a lake that the student had fond memories of, and was to have a glass top with slightly rounded corners to echo the base profile. Glass was ordered but didn't show up by the end of that semester when the photo was taken. 

4D

Wow, I quickly discovered several things:

 

There's a trick to cutting these shapes!  You've got to be a whole lot smarter than I am! Ya can't just cut any line where-evers you want.  There's an uphill and a downhill. You pick one and stick to it.

 

30˚ will get you half of an octahedron. In theory.  I practiced on Italian fine wine crate lids of kiln-dried pine, just time and electric.  On my new work bench, a diamond plate tool box on sawhorses. With the new window jam-next-to-the fan blocker thing, vac, lighting. Bench scroll and sander. Sort of a test run.

 

3 hours ago, Woodman said:

...With the new window jam-next-to-the fan blocker thing, ...

 

Oh man, you got one of those?

так.  Finest kind. Will have to speak to the electrician, though.

 

 

Love that work bench.  

3 hours ago, Gene Howe said:

Love that work bench.  

 

Yeah, GMC factory box. A freebie when my factory-ordered Sierra I did not actually order came into the dealership.  Kept the box when I went to an A.R.E. cap. Buddy with identical truck has been hounding me to sell / lend it. Makes a good spot to store the box, dedicated light-duty dedicated craft-tool surface. And it is perfect on the truck.