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Tag Archives: ball in a cage

My son, who is an engineer working on the design of big diesel engines, tells me that it’s all too easy, especially with CAD software, to draw what seems a brilliant plan – only to meet derision when someone realises that it can’t be manufactured. You can imagine the sort of thing he means: a nut where there isn’t enough space to get a spanner in to tighten it; or the need for a long bolt in a place with insufficient clearance to get it into the hole.

As someone who works with wood, I enjoy teasing him with the complete opposite: something that self-evidently has been manufactured but that looks impossible. One example is the captive screw here. But that’s a bit of a cheat because it depends on exploiting the remarkable elastic properties of some woods when treated with heat and moisture. Better are the apparently impossible double and triple dovetails that I wrote about a year or so ago.

Here’s something in the same vein that can be sculpted out of wood with nothing more than a sharp chisel. Or, should you have one handy, a 5-axis CNC milling machine will do the job almost as well – see here.

For larger images, click on the thumbnails.

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