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Chamfer (geometry)
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Chamfer (geometry)
Unchamfered, slightly chamfered, and chamfered cube
Historical crystal models of slightly chamfered Platonic solids

In geometry, a chamfer or edge-truncation is a topological operator that modifies one polyhedron into another. It separates the faces by reducing them, and adds a new face between each two adjacent faces (moving the vertices inward). Oppositely, similar to expansion, it moves the faces apart outward, and adds a new face between each two adjacent faces; but contrary to expansion, it maintains the original vertices.

For a polyhedron, this operation adds a new hexagonal face in place of each original edge.

In Conway polyhedron notation, chamfering is represented by the letter "c". A polyhedron with e edges will have a chamfered form containing 2e new vertices, 3e new edges, and e new hexagonal faces.

Platonic solids

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Left to right: chamfered tetrahedron, cube, octahedron, dodecahedron, and icosahedron

Chamfers of five Platonic solids are described in detail below.

Historical drawings of truncated tetrahedron and slightly chamfered tetrahedron.[1]
  • chamfered tetrahedron or alternated truncated cube: from a regular tetrahedron, this replaces its six edges with congruent flattened hexagons; or alternately truncating a cube, replacing four of its eight vertices with congruent equilateral-triangle faces. This is an example of Goldberg polyhedron GPIII(2,0) or {3+,3}2,0, containing triangular and hexagonal faces. Its dual is the alternate-triakis tetratetrahedron.[2]
  • chamfered cube: from a cube, the resulting polyhedron has twelve hexagonal and six square centrally symmetric faces, a zonohedron.[3] This is also an example of the Goldberg polyhedron GPIV(2,0) or {4+,3}2,0. Its dual is the tetrakis cuboctahedron. A twisty puzzle of the DaYan Gem 7 is the shape of a chamfered cube.[4]
  • chamfered octahedron or tritruncated rhombic dodecahedron: from a regular octahedron by chamfering,[5] or by truncating the eight order-3 vertices of the rhombic dodecahedron, which become congruent equilateral triangles, and the original twelve rhombic faces become congruent flattened hexagons. It is a Goldberg polyhedron GPV(2,0) or {5+,3}2,0. Its dual is triakis cuboctahedron.[2]
pentakis icosidodecahedron and triakis icosidodecahedron

Regular tilings

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Chamfered regular and quasiregular tilings

Square tiling, Q
{4,4}

Triangular tiling, Δ
{3,6}

Hexagonal tiling, H
{6,3}

Rhombille, daH
dr{6,3}
cQ cH cdaH

Relation to Goldberg polyhedra

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The chamfer operation applied in series creates progressively larger polyhedra with new faces, hexagonal, replacing the edges of the current one. The chamfer operator transforms GP(m,n) to GP(2m,2n).

A regular polyhedron, GP(1,0), creates a Goldberg polyhedra sequence: GP(1,0), GP(2,0), GP(4,0), GP(8,0), GP(16,0)...

GP(1,0) GP(2,0) GP(4,0) GP(8,0) GP(16,0) ...
GPIV
{4+,3}

C

cC

ccC

cccC

ccccC
...
GPV
{5+,3}

D

cD

ccD

cccD

ccccD
...
GPVI
{6+,3}

H

cH

ccH

cccH

ccccH
...

The truncated octahedron or truncated icosahedron, GP(1,1), creates a Goldberg sequence: GP(1,1), GP(2,2), GP(4,4), GP(8,8)...

GP(1,1) GP(2,2) GP(4,4) ...
GPIV
{4+,3}

tO

ctO

cctO
...
GPV
{5+,3}

tI

ctI

cctI
...
GPVI
{6+,3}


ctΔ

cctΔ
...

A truncated tetrakis hexahedron or pentakis dodecahedron, GP(3,0), creates a Goldberg sequence: GP(3,0), GP(6,0), GP(12,0)...

GP(3,0) GP(6,0) GP(12,0) ...
GPIV
{4+,3}

tkC

ctkC

cctkC
...
GPV
{5+,3}

tkD

ctkD

cctkD
...
GPVI
{6+,3}

tkH

ctkH

cctkH
...

See also

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References

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  1. ^ Spencer 1911, p. 575, or p. 597 on Wikisource, Crystallography, 1. Cubic System, Tetrahedral Class, Figs. 30 & 31.
  2. ^ a b c d Deza, Deza & Grishukhin 1998, 3.4.3. Edge truncations.
  3. ^ Gelişgen & Yavuz 2019b, Chamfered Cube Metric and Some Properties.
  4. ^ "TwistyPuzzles.com > Museum > Show Museum Item". twistypuzzles.com. Retrieved 2025-02-09.
  5. ^ Gelişgen & Yavuz 2019b, Chamfered Octahedron Metric and Some Properties.
  6. ^ Gelişgen & Yavuz 2019a.

Sources

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