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Saturday, 13 February 2021

Icosahedron from construction kit, part 1

 

Truncated icosahedron of the type I will be making.

This table for designing truncation pieces this was used to design the extra square sides of ....
this octahedron (about 42mm from edge holdes on squares to centres)


and the planned icosahedron faces....

with edge holders 57.2mm from centre.

The round timber pieces were cut using holesaws to cut through.....

3mm plywood.....

in this large drill.

Graphical image of truncations of cd polygons.


Hi, as described in posts here and here and here, I have been experimenting making regular platonic solids using cds as a base, but haven't yet cracked the 20 sided, triangle sided icosahedron. But a bit of work making a truncated, reinforced octahedron made me realise the reinforcing truncation sides could be made quite easily. 

The octahedron only needed 6 extra square truncation sides and I made them from bicycle sprockets of varying sizes. There was a bit of effort designing and making 3 different types of matching surrounds for the sprockets. With 12 truncation sides, the icosahedron really needed a uniform truncation side.

Eventually I wandered out to the shed, grabbed my big, (mostly intact!) holesaws and worked out which holesaw would cut the best truncation sides. Then I made a sample side, and designed and printed an edge adapter for it, using the spreadsheet and graphic 57.5mm measurement as one of the dimensions.

So the sides worked out ok, and I was ready to start making more parts. The round part of the truncation side came first, I was all set up to make that with the holesaw already in the drill. (to be continued)

regards


Steve Nurse

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