Burr puzzle
Quality burr puzzles are usually precision-made for easy sliding and accurate fitting of the pieces.
The term "burr" is first mentioned in a 1928 book by Edwin Wyatt,[1] but the text implies that it was commonly used before.
[8] For many years, the six-piece burr was very common and popular, but was considered trite and uninteresting by enthusiasts.
Most of the puzzles made and sold were very similar to one another and most of them included a "key" piece, an unnotched stick that slides easily out.
In the late 1970s, however, the six-piece burr regained the attention of inventors and collectors, thanks largely to a computer analysis conducted by the mathematically trained puzzle designer Bill Cutler which was published by Martin Gardner in his Mathematical Games column in Scientific American.
The notches of all sticks are located within the region of intersection, so when the puzzle is assembled they are unseen.
This set, often referred to as "The 25 notchable pieces", with the addition of 17 duplicates, can be assembled to create 221 different solid burr puzzles.
[13] In 1990, Cutler completed the final part of his analysis and found that the highest possible level using notchable pieces is 5, and 139 of those puzzles exist.
The highest level possible for a six-piece burr with more than one solution is 12, meaning 12 moves are required to remove the first piece.
[15] There are, however, some three-piece burrs with different kinds of notches, the best known of them being the one mentioned by Wyatt in his 1928 book, consisting of a rounded piece that is meant to be rotated.
[16] The name "Altekruse" is of Austrian-German origin and means "old-cross" in German, which led to the presumption that it was a pseudonym, but a man by that name immigrated to America in 1844 with his three brothers to avoid being drafted to the Prussian Army and is presumed to be the one who filed this patent.
Despite their size, those bigger puzzles are not considered very difficult, yet they require patience and dexterity to assemble.
The Chuck can also be regarded as an extension of a six-piece burr of very simple pieces called Baby-chuck, which is very easy to solve.
Chuck pieces of different lengths can also be used to create asymmetric shapes, assembled according to the same principle as the original puzzle.
[1] Puzzles of this family can be regarded as an extension of the "three-piece burr" (Pagoda of size 1), however they do not require special notches to be assembled or taken apart.
