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Example post: Burr No. 305
Burr No. 305, assembled

Example post: Burr No. 305

·328 words·2 mins
Unknown Burr Six-Piece Burr Solid Burr Example
Table of Contents
Designer
Unknown
Maker
Not built yet: OpenSCAD renders
Type
Burr
Pieces
6
Level
1

This is a worked example of a puzzle post on Next Piece. It will be replaced by real posts soon. The puzzle is a real one, though: Burr No. 305 from Bill Cutler’s tabulation of the 314 solid notchable six-piece burrs.

A six-piece burr is three pairs of notched 2×2×6 sticks crossing at right angles. Solid means the six sticks fill the burr shape completely: 104 cubes and not one gap. With no room to wiggle, the very first move has to take the puzzle apart, which makes it a level-1 burr. The sticks are named by their Känel numbers, a compact code for a stick’s notches: 52, 615, 792, 960, 975, 992. They fit together in exactly one way.

The pieces
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Assembled
Assembled
The six sticks laid flat. Red 52, blue 615, yellow 792, green 960, orange 975, purple 992.
The six sticks laid flat. Red 52, blue 615, yellow 792, green 960, orange 975, purple 992.

Turn it around
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The pieces pulled apart from the centre so you can see how the notches meet.

Burr No. 305, exploded view. Drag to rotate · scroll or pinch to zoom

Taking it apart
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Every separation below is a single straight slide, checked by a search over all the ways each group of sticks can move.

  1. Red, green and purple (52, 960 and 992) slide out together along the red stick.
    Step 1: Red, green and purple (52, 960 and 992) slide out together along the red stick.
  2. One move later the burr is in two halves of three sticks.
    Step 2: One move later the burr is in two halves of three sticks.
  3. Each half gives up one stick: red slides sideways out of its half, yellow lifts out of the other.
    Step 3: Each half gives up one stick: red slides sideways out of its half, yellow lifts out of the other.
  4. The last two pairs come apart: green from purple, blue from orange.
    Step 4: The last two pairs come apart: green from purple, blue from orange.

How the images were made
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The sticks were generated from the six Känel numbers, checked to have exactly one assembly, rendered in OpenSCAD and converted to a coloured GLB for the viewer with the blog’s tools/stl2glb.py. The colours are PLA filaments in stock, so a printed copy can match.