Chamfer (geometry)

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Polyhedron 6 unchamfered.png
Polyhedron 6 slightly chamfered.png
Polyhedron chamfered 6 edeq.png
Unchamfered, slightly chamfered, and chamfered cube
Modell, Kristallform Tetraeder-Tetraeder -Krantz 394-.jpg
Modell, Kristallform Wurfel-Rhombendodekaeder -Krantz 428-.jpg
Modell, Kristallform Oktaeder-Rhombendodekaeder -Krantz 432-.jpg
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 inward.) For a polyhedron, this operation adds a new hexagonal face in place of each original edge.

Contents

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 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.

Seed
Platonic
solid
Polyhedron 4a.png Polyhedron 4b.png
{3,3}
Polyhedron 6.png
{4,3}
Polyhedron 8.png
{3,4}
Polyhedron 12.png
{5,3}
Polyhedron 20.png
{3,5}
Chamfered
Platonic
solid
(equilateral
form)
Polyhedron chamfered 4a edeq.png Polyhedron chamfered 4b edeq.png Polyhedron chamfered 6 edeq.png Polyhedron chamfered 8 edeq.png Polyhedron chamfered 12 edeq.png Polyhedron chamfered 20 edeq.png

Chamfered tetrahedron

Chamfered tetrahedron
Polyhedron chamfered 4a edeq max.png
(equilateral form)
Conway notation cT
Goldberg polyhedron GPIII(2,0) = {3+,3}2,0
Faces4 congruent equilateral triangles
6 congruent equilateral* hexagons
Edges24 (2 types:
triangle-hexagon,
hexagon-hexagon)
Vertices16 (2 types)
Vertex configuration (12) 3.6.6
(4) 6.6.6
Symmetry group Tetrahedral (Td)
Dual polyhedron Alternate-triakis tetratetrahedron
Properties convex, equilateral*
Polyhedron chamfered 4a net.svg
Net
*for a certain chamfering/truncating depth

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

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

The dual of the chamfered tetrahedron is the alternate-triakis tetratetrahedron.

The cT is the Goldberg polyhedron GPIII(2,0) or {3+,3}2,0, containing triangular and hexagonal faces.

The truncated tetrahedron looks similar; but its hexagons correspond to the 4 faces, not to the 6 edges, of the yellow tetrahedron, i.e. to the 4 vertices, not to the 6 edges, of the red tetrahedron. Polyhedron truncated 4b max.png
The truncated tetrahedron looks similar; but its hexagons correspond to the 4 faces, not to the 6 edges, of the yellow tetrahedron, i.e. to the 4 vertices, not to the 6 edges, of the red tetrahedron.
Historical drawings of truncated tetrahedron and slightly chamfered tetrahedron. EB1911 Crystallography Figs. 30 & 31.jpg
Historical drawings of truncated tetrahedron and slightly chamfered tetrahedron.
Tetrahedral chamfers and their duals
Polyhedron chamfered 4a.png
chamfered tetrahedron
(canonical form)
Polyhedron 4-4 dual.png
dual of the tetratetrahedron
Polyhedron chamfered 4b.png
chamfered tetrahedron
(canonical form)
Polyhedron chamfered 4a dual.png
alternate-triakis tetratetrahedron
Polyhedron 4-4.png
tetratetrahedron
Polyhedron chamfered 4b dual.png
alternate-triakis tetratetrahedron

Chamfered cube

Chamfered cube
Polyhedron chamfered 6 edeq max.png
(equilateral form)
Conway notation cC = t4daC
Goldberg polyhedron GPIV(2,0) = {4+,3}2,0
Faces6 congruent squares
12 congruent equilateral* hexagons
Edges48 (2 types:
square-hexagon,
hexagon-hexagon)
Vertices32 (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*
Truncated rhombic dodecahedron net.png
Net (3 zones are shown by 3 colors for their hexagons — each square is in 2 zones —.)
*for a certain chamfering depth

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 chamfered cube have the same length; then, the hexagons are equilateral, but not regular. They are congruent alternately truncated rhombi, have 2 internal angles of and 4 internal angles of while a regular hexagon would have all internal angles.

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.

The dual of the chamfered cube is the tetrakis cuboctahedron.

Because all the faces of the cC have an even number of sides and are centrally symmetric, it is a zonohedron:

Chamfered cube (3 zones are shown by 3 colors for their hexagons -- each square is in 2 zones --.) Truncated rhombic dodecahedron.png
Chamfered cube (3 zones are shown by 3 colors for their hexagons — each square is in 2 zones —.)

The chamfered cube 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 and its six order-4 vertices are at the permutations of

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.

Polyhedron pyritohedron.png
Polyhedron chamfered 6 pyritohedral.png
Pyritohedron and its axis truncation
Modelle, Kristallform Wurfel-Pentagondodekaeder -Krantz 379, 380- (2).jpg
Modelle, Kristallform Wurfel-Pentagondodekaeder -Krantz 379, 380- (4).jpg
Historical crystallographic models of axis shallower and deeper truncations of pyritohedron
The truncated octahedron looks similar; but its hexagons correspond to the 8 faces, not to the 12 edges, of the octahedron, i.e. to the 8 vertices, not to the 12 edges, of the cube. Polyhedron truncated 8 max.png
The truncated octahedron looks similar; but its hexagons correspond to the 8 faces, not to the 12 edges, of the octahedron, i.e. to the 8 vertices, not to the 12 edges, of the cube.
Octahedral chamfers and their duals
Polyhedron chamfered 6.png
chamfered cube
(canonical form)
Polyhedron 6-8 dual.png
rhombic dodecahedron
Polyhedron chamfered 8.png
chamfered octahedron
(canonical form)
Polyhedron chamfered 6 dual.png
tetrakis cuboctahedron
Polyhedron 6-8.png
cuboctahedron
Polyhedron chamfered 8 dual.png
triakis cuboctahedron

Chamfered octahedron

Chamfered octahedron
Polyhedron chamfered 8 edeq max.png
(equilateral form)
Conway notation cO = t3daO
Faces8 congruent equilateral triangles
12 congruent equilateral* hexagons
Edges48 (2 types:
triangle-hexagon,
hexagon-hexagon)
Vertices30 (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*
*for a certain truncating depth

In geometry, the chamfered octahedron 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.

The chamfered octahedron can also be called a tritruncated rhombic dodecahedron.

The dual of the cO is the triakis cuboctahedron.

Historical drawings of rhombic dodecahedron and slightly chamfered octahedron Brockhaus and Efron Encyclopedic Dictionary b48 862-4.jpg
Historical drawings of rhombic dodecahedron and slightly chamfered octahedron
Modell, Kristallform Wurfel-Deltoidikositetraeder -Krantz 426-.jpg
Modell, Kristallform Oktaeder-Rhombendodekaeder -Krantz 432-.jpg
Historical models of triakis cuboctahedron and slightly chamfered octahedron

Chamfered dodecahedron

Chamfered dodecahedron
Polyhedron chamfered 12 edeq max.png
(equilateral form)
Conway notation cD = t5daD = dk5aD
Goldberg polyhedron GPV(2,0) = {5+,3}2,0
Fullerene C80 [2]
Faces12 congruent regular pentagons
30 congruent equilateral* hexagons
Edges120 (2 types:
pentagon-hexagon,
hexagon-hexagon)
Vertices80 (2 types)
Vertex configuration (60) 5.6.6
(20) 6.6.6
Symmetry group Icosahedral (Ih)
Dual polyhedron Pentakis icosidodecahedron
Properties convex, equilateral*
*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 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.

The dual of the chamfered dodecahedron is the pentakis icosidodecahedron.

The cD is the Goldberg polyhedron GPV(2,0) or {5+,3}2,0, containing pentagonal and hexagonal faces.

The truncated icosahedron looks similar, but its hexagons correspond to the 20 faces, not to the 30 edges, of the icosahedron, i.e. to the 20 vertices, not to the 30 edges, of the dodecahedron. Polyhedron truncated 20 max.png
The truncated icosahedron looks similar, but its hexagons correspond to the 20 faces, not to the 30 edges, of the icosahedron, i.e. to the 20 vertices, not to the 30 edges, of the dodecahedron.
Icosahedral chamfers and their duals
Polyhedron chamfered 12.png
chamfered dodecahedron
(canonical form)
Polyhedron 12-20 dual.png
rhombic triacontahedron
Polyhedron chamfered 20.png
chamfered icosahedron
(canonical form)
Polyhedron chamfered 12 dual.png
pentakis icosidodecahedron
Polyhedron 12-20.png
icosidodecahedron
Polyhedron chamfered 20 dual.png
triakis icosidodecahedron

Chamfered icosahedron

Chamfered icosahedron
Polyhedron chamfered 20 edeq max.png
(equilateral form)
Conway notation cI = t3daI
Faces20 congruent equilateral triangles
30 congruent equilateral* hexagons
Edges120 (2 types:
triangle-hexagon,
hexagon-hexagon)
Vertices72 (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*
*for a certain truncating depth

In geometry, the chamfered icosahedron 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, with a certain depth of truncation.

The chamfered icosahedron can also be called a tritruncated rhombic triacontahedron.

The dual of the cI is the triakis icosidodecahedron.

Chamfered regular tilings

Chamfered regular and quasiregular tilings
Tiling 4a simple.svg
Square tiling, Q
{4,4}
Tiling 3 simple.svg
Triangular tiling, Δ
{3,6}
Tiling 6 simple.svg
Hexagonal tiling, H
{6,3}
Tiling 3-6 dual.svg
Rhombille, daH
dr{6,3}
Chamfer square tiling.svg Chamfer triangular tiling.svg Chamfer hexagonal tiling.svg Chamfered rhombille tiling.svg
cQ cH cdaH

Relation to Goldberg polyhedra

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}
Uniform polyhedron-43-t0.svg
C
Truncated rhombic dodecahedron2.png
cC
Octahedral goldberg polyhedron 04 00.svg
ccC
Octahedral goldberg polyhedron 08 00.svg
cccC

ccccC
...
GPV
{5+,3}
Uniform polyhedron-53-t0.svg
D
Truncated rhombic triacontahedron.png
cD
Chamfered chamfered dodecahedron.png
ccD
Chamfered chamfered chamfered dodecahedron.png
cccD
Chamfered chamfered chamfered chamfered dodecahedron.png
ccccD
...
GPVI
{6+,3}
Tiling 6 simple.svg
H
Truncated rhombille tiling.svg
cH
Chamfered chamfered hexagonal tiling.png
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}
Uniform polyhedron-43-t12.svg
tO
Chamfered truncated octahedron.png
ctO
Chamfered chamfered truncated octahedron.png
cctO
...
GPV
{5+,3}
Uniform polyhedron-53-t12.svg
tI
Chamfered truncated icosahedron.png
ctI
Chamfered chamfered truncated icosahedron.png
cctI
...
GPVI
{6+,3}
Uniform tiling 63-t12.svg
Chamfered truncated triangular tiling.svg
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}
Octahedral goldberg polyhedron 03 00.svg
tkC
Octahedral goldberg polyhedron 06 00.svg
ctkC

cctkC
...
GPV
{5+,3}
Conway polyhedron Dk6k5tI.png
tkD
Chamfered truncated pentakis dodecahedron.png
ctkD

cctkD
...
GPVI
{6+,3}
Truncated hexakis hexagonal tiling.png
tkH
Chamfered truncated hexakis hexagonal tiling.svg
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. Example:

A chamfered square
(See also the previous version of this figure.) Chamfered square.png
A chamfered square
(See also the previous version of this figure.)

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.[something may be wrong in this passage]

See also

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References

  1. Spencer 1911, p. 575, or p. 597 on Wikisource, CRYSTALLOGRAPHY, 1. CUBIC SYSTEM, TETRAHEDRAL CLASS, FIGS. 30 & 31.
  2. "C80 Isomers". Archived from the original on 2014-08-12. Retrieved 2014-08-09.

Sources