Sunday, 7 August 2011

L-Bert Hall

Ronald Kint-Bruynseels entered this puzzle in the IPP 27 Design Competition under the full title “(Now they know how many holes it takes to fill) The L-Bert Hall” in a great take on the line from the Beatles classic “A day in the life”. The puzzles were made by Eric Fuller who subsequently offered 30 copies for sale on Cubic Dissection in October 2007. Eric’s description at the time mentioned that he was quite proud of the results and made specific reference to the box tolerances being “close for a nice fit”.
My walnut and quilted maple copy came from a recent Cubic Dissection Auction and I was very chuffed when I managed to secure it with a reasonable bid.
Four years on, there’s still a lot of evidence of those close tolerances – half of the pieces refused to exit box when it arrived in Blighty, despite my ‘encouragement’ of the agricultural variety! A few days on the windowsill in the full, mighty glare of the English sun (40W equivalent for those of you not familiar with this particular phenomenon) had loosened the pieces sufficiently to allow a more elegant exit.
Ostensibly this is a really simple little puzzle made up of nine identical pieces: three blocks in an L-shape with a perpendicular dowel protruding from one block and holes drilled through the other two blocks. The aim is to build a 3*3*3 cube to fit in the (rather snug) box (so clearly the dowels can’t face outwards, but I like your thinking!).
Intuitively it feels like it should be a fairly simple puzzle, and indeed, if those jolly dowels weren’t there it would be! Burr Tools confirms that if the dowels weren’t there, there would be 111 ways of arranging those pieces into a cube, however, the introduction of those dowels makes the solution unique(!).
I haven’t managed to come up with a clever way of deducing what the answer must look like (any suggestions from anyone “out there”?), so I’ve been reduced to a form of brute-force attack – but thankfully there are only 9 pieces, and they’re identical, so you can crank through alternatives fairly efficiently…
…a couple of weeks on and the fit is still extremely snug, so I’m airing the pieces on the windowsill for a while longer – with the fierce English sun burning down on them I’m sure that when winter arrives and the central heating really kicks in they’ll be back to designer specifications.


  1. Great review Allard. If it persists in being so snug, take it to work for a while, or some other place that is air conditioned. The lower moisture in AC environments tends to cause the puzzle to shrink. Check it often and then take it home again when it fits better...I usually bring along a zip-loc plastic bag too so I can seal it up when it fits OK. Hope this helps!

  2. Thanks Scott - and thanks for the advice. [Sod's law says I work in England in one of those eco-friendly buildings with 'natural air-conditioning' - but I'll seek out an air- conditioned place to leave them for a while.]