The following is taken from the original post on TwistyPuzzles.com on 2/18/2010.
Here is the Icosmate!
I have mentioned a couple of times that my original idea for the pentultimate was for the icosahedron shape. I have finally made one! I thought it would also be fun to include below some of my original sketches for the puzzle, before I knew of the name “Pentultimate”, and some of my original knucklehead musings and scribbles. One of the sketches is for a deep cut edge turning icosahedron, which I haven’t tackled yet.
I called this version 2.5 of the mechanism for awhile. But since it works great, I’ve started just giving it its own version number, v3.
In the skirting rails mechanism, an internal void master version of the desired puzzle is made. The master layer will be hidden and never allowed to turn. The master layer will only be allowed to skirt sideways.
There are eight types of pieces including the caps and core.
Something about my camera during this period of time caused my images to be soft and blurry. Sorry!
To enforce the rule that the rails can only skirt sideways, the void master layer is glued around the top center. This takes care of five of the six master pentultimate rings.
Here the top center has been glued to it’s adjacent master parts (in white). It will be attached to the core (in grey) and locked in place.
Here the fixed center and adjacent glued rails have been attached.
To enforce the ring of void parts on the equator, that aren’t locked in place by touching the top center, some blocking shapes are added to the core. Shown here in blue is the small part that will be fixed to the core and stop the adjacent master piece from moving in the slice direction.
If you look again at the photos above, you can see the blockers on the equator of the core.
Here, half the puzzle has been assembled. Since it’s a void mechanism, the core isn’t needed to hold these parts together.
Here the equator blockers are visible, as well as the feet that can interact with them.