# Chamfer (geometry)

Unchamfered, slightly chamfered, and chamfered cube
Historical crystal models of slightly chamfered Platonic solids

In geometry, chamfering or edge-truncation is a topological operator that modifies one polyhedron into another. It is 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. (Equivalently: it separates the faces by reducing them, and adds a new face between each two adjacent faces; but it only moves the vertices lower.) 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.

## Chamfered Platonic solids

In the chapters below, the chamfers of the five Platonic solids are described in detail. Each is shown in an equilateral-faced version where all edges have the same length, and in a canonical version where all edges touch the same midsphere. (They look noticeably different only for solids containing triangles.) The shown dual polyhedra are dual to the canonical versions.

 SeedPlatonicsolid ChamferedPlatonicsolid {3,3} {4,3} {3,4} {5,3} {3,5}

### Chamfered tetrahedron

Chamfered tetrahedron

(equilateral-faced form)
Conway notation cT
Goldberg polyhedron GPIII(2,0) = {3+,3}2,0
Faces 4 congruent equilateral triangles
6 congruent hexagons (equilateral for a certain chamfering depth)
Edges 24 (2 types:
triangle-hexagon,
hexagon-hexagon)
Vertices 16 (2 types)
Vertex configuration (12) 3.6.6
(4) 6.6.6
Symmetry group Tetrahedral (Td)
Dual polyhedron Alternate-triakis tetratetrahedron
Properties convex, equilateral-faced (for a certain chamfering depth)

Net

The chamfered tetrahedron or alternate truncated cube is a convex polyhedron constructed:

For a certain depth of truncation/chamfering, all (final) edges of the cT have the same length; then, the hexagons are equilateral, but not regular.

The chamfered tetrahedron is the Goldberg polyhedron GIII(2,0), containing triangular and hexagonal faces.

 chamfered tetrahedron(canonical form) dual of the tetratetrahedron chamfered tetrahedron(canonical form) alternate-triakis tetratetrahedron tetratetrahedron alternate-triakis tetratetrahedron

### Chamfered cube

Chamfered cube

(equilateral-faced form)
Conway notation cC = t4daC
Goldberg polyhedron GPIV(2,0) = {4+,3}2,0
Faces 6 congruent squares
12 congruent hexagons (equilateral for a certain chamfering depth)
Edges 48 (2 types:
square-hexagon,
hexagon-hexagon)
Vertices 32 (2 types)
Vertex configuration (24) 4.6.6
(8) 6.6.6
Symmetry Oh, [4,3], (*432)
Th, [4,3+], (3*2)
Dual polyhedron Tetrakis cuboctahedron
Properties convex, equilateral-faced (for a certain chamfering depth)

Net (3 zones are shown by 3 colors for their hexagons — each square is in 2 zones —.)

The chamfered cube is constructed as a chamfer of a cube: the squares are reduced in size and new faces, hexagons, are added in place of all the original edges. The cC is a convex polyhedron with 32 vertices, 48 edges, and 18 faces: 6 congruent (and regular) squares, and 12 congruent flattened hexagons.
For a certain depth of chamfering, all (final) edges of the cC have the same length; then, the hexagons are equilateral, but not regular. They are congruent partly truncated rhombi, have 2 internal angles of ${\displaystyle \cos ^{-1}(-{\frac {1}{3}})\approx 109.47^{\circ }}$ and 4 internal angles of ${\displaystyle \pi -{\frac {1}{2}}\cos ^{-1}(-{\frac {1}{3}})\approx 125.26^{\circ },}$ while a regular hexagon would have all ${\displaystyle 120^{\circ }}$ internal angles.

The dual of the chamfered cube is the tetrakis cuboctahedron.

The cC is also inaccurately called a truncated rhombic dodecahedron, although that name rather suggests a rhombicuboctahedron. The cC can more accurately be called a tetratruncated rhombic dodecahedron, because only the (6) order-4 vertices of the rhombic dodecahedron are truncated.

Because all the faces of the chamfered cube have an even number of sides and are centrally symmetric, it is a zonohedron. It is also the Goldberg polyhedron GPIV(2,0) or {4+,3}2,0, containing square and hexagonal faces.

The cC is the Minkowski sum of a rhombic dodecahedron and a cube of edge length 1 when the eight order-3 vertices of the rhombic dodecahedron are at ${\displaystyle (\pm 1,\pm 1,\pm 1)}$ and its six order-4 vertices are at the permutations of ${\displaystyle (\pm {\sqrt {3}},0,0).}$

A topological equivalent to the chamfered cube but with pyritohedral symmetry and rectangular faces can be constructed by chamfering the axial edges of a pyritohedron. This occurs in pyrite crystals.

 Pyritohedron and its axis truncation Historical crystallographic models of axis shallower and deeper truncations of pyritohedron
 chamfered cube(canonical form) rhombic dodecahedron chamfered octahedron(canonical form) tetrakis cuboctahedron cuboctahedron triakis cuboctahedron

### Chamfered octahedron

Chamfered octahedron

(equilateral-faced form)
Conway notation cO = t3daO
Faces 8 congruent equilateral triangles
12 congruent hexagons (equilateral for a certain chamfering depth)
Edges 48 (2 types:
triangle-hexagon,
hexagon-hexagon)
Vertices 30 (2 types)
Vertex configuration (24) 3.6.6
(6) 6.6.6.6
Symmetry Oh, [4,3], (*432)
Dual polyhedron Triakis cuboctahedron
Properties convex, equilateral-faced (for a certain chamfering depth)

In geometry, the chamfered octahedron or tritruncated rhombic dodecahedron is a convex polyhedron constructed by truncating the 8 order-3 vertices of the rhombic dodecahedron. These truncated vertices become congruent equilateral triangles, and the original 12 rhombic faces become congruent flattened hexagons.
For a certain depth of truncation, all (final) edges of the cO have the same length; then, the hexagons are equilateral, but not regular.

Historical models of triakis cuboctahedron and slightly chamfered octahedron

### Chamfered dodecahedron

Chamfered dodecahedron

(equilateral-faced form)
Conway notation cD = t5daD = dk5aD
Goldberg polyhedron GV(2,0) = {5+,3}2,0
Fullerene C80[2]
Faces 12 congruent regular pentagons
30 congruent hexagons (equilateral for a certain chamfering depth)
Edges 120 (2 types:
pentagon-hexagon,
hexagon-hexagon)
Vertices 80 (2 types)
Vertex configuration (60) 5.6.6
(20) 6.6.6
Symmetry group Icosahedral (Ih)
Dual polyhedron Pentakis icosidodecahedron
Properties convex, equilateral-faced (for a certain chamfering depth)

The chamfered dodecahedron is a convex polyhedron with 80 vertices, 120 edges, and 42 faces: 12 congruent regular pentagons and 30 congruent flattened hexagons.
It is constructed as a chamfer of a regular dodecahedron. The pentagons are reduced in size and new faces, flattened hexagons, are added in place of all the original edges. For a certain depth of chamfering, all (final) edges of the cD have the same length; then, the hexagons are equilateral, but not regular.
The dual of the chamfered dodecahedron is the pentakis icosidodecahedron.

The cD is also inaccurately called a truncated rhombic triacontahedron, although that name rather suggests a rhombicosidodecahedron. The cD can more accurately be called a pentatruncated rhombic triacontahedron, because only the (12) order-5 vertices of the rhombic triacontahedron are truncated.

 chamfered dodecahedron(canonical form) rhombic triacontahedron chamfered icosahedron(canonical form) pentakis icosidodecahedron icosidodecahedron triakis icosidodecahedron

### Chamfered icosahedron

Chamfered icosahedron

(equilateral-faced form)
Conway notation cI = t3daI
Faces 20 congruent equilateral triangles
30 congruent hexagons (equilateral for a certain chamfering depth)
Edges 120 (2 types:
triangle-hexagon,
hexagon-hexagon)
Vertices 72 (2 types)
Vertex configuration (24) 3.6.6
(12) 6.6.6.6.6
Symmetry Ih, [5,3], (*532)
Dual polyhedron Triakis icosidodecahedron
Properties convex, equilateral-faced (for a certain chamfering depth)

In geometry, the chamfered icosahedron or tritruncated rhombic triacontahedron is a convex polyhedron constructed by truncating the 20 order-3 vertices of the rhombic triacontahedron. The hexagonal faces of the cI can be made equilateral, but not regular.

## Chamfered regular tilings

 Square tiling, Q{4,4} Triangular tiling, Δ{3,6} Hexagonal tiling, H{6,3} Rhombille, daHdr{6,3} cQ cΔ cH cdaH

## Relation to Goldberg polyhedra

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

A regular polyhedron, GP(1,0), create 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
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}

tH

ctH

cctH

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

## Chamfered polytopes and honeycombs

Like the expansion operation, chamfer can be applied to any dimension. For polygons, it triples the number of vertices. For polychora, new cells are created around the original edges. The cells are prisms, containing two copies of the original face, with pyramids augmented onto the prism sides.