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Why does my capstone wobble?
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nigelswift
8112 posts

Why does my capstone wobble?
Feb 07, 2004, 11:37
Having made a very small dolmen out of rocks in the garden today, something became clear: it's the devil's own job to get the capstone to rest evenly on all of the uprights, one or more of them is always too high or low and it wobbles and if you start again and make one of the uprights higher then another one becomes the wrong fit.
But proper dolmens are rarely like that, the capstone rests on all the uprights.
(Here's an exception) http://www.themodernantiquarian.com/post/14908

Does this give an indication of how they were made? The only way to do it that I can think of is to raise the capstone on wood first and then insert each upright from the side and hammer it sideways until it's tightly wedged. If one of the others then goes wrong you hammer that some more.

If it wasn't done this way, shouldn't most rather than a few have packing pieces? (Or do they?) Bear in mind, it's not just a case of getting the tops of the uprights into the same plane, the underside of the capstone is uneven so getting them to fit in advance would stretch the abilities of even a modern engineer.
Has anyone noticed any evidence of bits of the capstone broken near the uprights suggesting this method might have been used?

Might the use of this method explain why so many uprights were selected to be pointed? It's not what you'd do if you wanted to maximise structural stability but it would make it easier to hammer it sideways. It also happens to be the optimum method that would ensure longevity - the weight distribution becomes pretty even, so the chances of long-term settlement through overloading of one of the uprights is less. You couldn't get that effect if you just plonked the capstone down.

Witnessing a modern dolmen making exercise,
http://66.102.11.104/search?q=cache:Bb3hiiw6L9gJ:www.britarch.ac.uk/ba/ba20/ba20news.html+dolmen+construction+method&hl=en&start=5&ie=UTF-8
Mr Burl suggested "The idea that the capstone was raised before the uprights also makes sense of the fact that one upright in a portal dolmen is usually pointed.... that allows the capstone to be swivelled from that upright onto the other two". I prefer my explanation, especially as more than one are usually pointed, but he's Mr Burl and I'm just a humble carpenter... ;)
Seems like another job for Gordon and the Stonehengineers, trying it different ways.
Replies:
Re: Why does my capstone wobble? (Mr Hamhead)
Re: Why does my capstone wobble? (Steve Gray)
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