Wednesday 6 February 2013

Maths Challenge

Here's a maths challenge for you,
How do you make a regular tetrahedron from square stock?
The crux of the problem is the compound mitre joint that must be cut.
There is a 54 and 30 degree angle in there somewhere from memory.
I suppose I have not figured out the jig - I only have a band saw and circular saw, neither very good, made many jigs for this, feel silly really...
Also you can construct an equilateral triangle from square stock....
Just  by using a 45 degree mitre saw...
I was happy when I figured that one out!

Quick Update
Just thought I would add that this is my 222nd post.
The number 2 is very important to me.
Might be a while till I get to 2222....


  1. Berin,

    To make a regular tetrahedron from square stock, I'd lay it out and cut it by hand.

    Doesn't a equilateral triangle have three 60-degree corners?


  2. Hi Chris,
    By this I presume you mean cut a 30 degree mitre on each piece?
    Unfortunately it does not work...
    The angle between 2 faces is 70.5288, so you would think half of this would work...
    Unfortunately it does not...
    I should not let my GCSE students make such complicated stuff. We solved it with making it from regular triangles, but I never got the jig to work accurately for square stock production. I will post some pics of the jigs at some point. I just don't have time to solve all this properly as I am so busy.
    All the best!

  3. Berin,

    I am thinking layout and you are thinking about cutting it with revealed reference surfaces. I think we're both right.


    PS: If you like geometric shapes and mitres and other complications, you might like this table base I designed and intend to make.