The Megalith Movers Prehistoric Engineering
Blog 29th August 2015    On Monday we had a team of four constructing the cantilever, or to be more accurate, transforming the bottom of the obelisk into a cantilevered base.    Steve and myself were first to show, followed by Sean and Joe who arrived at the same time. Sean with his engineering background understood immediately what we were trying to achieve and he and Joe pitched in to help. It wasn't long however, before Sean could see problems with the idea,     “I know you've fastened it tightly to the obelisk with lots of windlasses Gordon but when it gets to a steep angle the weight of the whole thing could cause the thing to slide and perhaps slide off he the end completely, if that happens the obelisk could come crashing down again”.    “OK Sean I can see that, let's take a break and think about it”.    After about 15 minutes I had an idea, “We can make a yoke and fasten it to the obelisk further up, if we again use plenty of windlasses we can make it really tight and because the obelisk is tapered the yoke will be unable to slide down. We can then, again using as much rope as is required, fasten the cantilever   timbers to the yoke”.    “Sean, can you tie a lorry drivers hitch?”, I continued.    “Yes no problem, but did you know they have been banned in Australia, too much risk of slippage if the load shifts, they now use webbing straps. A few of those would be good, each one will hold up to 2,000 pounds”. replied Sean.    “Probably banned in England as well, everything else is, but they weren't banned in Egypt 4,000 years ago, and anyway we aren't using them on the road”, I said.    By Tuesday we had finished the main cantilever platform and had attached  a box like structure made from the remaining timbers, to house whatever blocks of concrete or sandbags we needed to bring the cantilever into balance with the rest of the obelisk. Sean didn't turn up on Tuesday, but by the end of the work period we had started filling the box. Steve and Joe were now almost as enthusiastic as myself about the possibilities.    On Wednesday by six a.m. it was raining, and as time went on became heavier, we cancelled work for the day. I used the time for thinking, and by the time the rain had stopped I had an alternative to the lorry drivers hitch. My first wife had once worked in a weaving mill and because of this I knew a little about weaving. The longitude threads on a loom are called the warp threads and the horizontal threads are called the weft threads. We could use rope arranged as the warp threads between the yoke and the cantilever timbers, we could bind one continuous rope round and round between the two, and then tie another rope horizontally across the middle, pulling the warp ropes together, like a bow in a pretty girl's hair. The rope we were using would easily bear the weight of a full bag of sand, say, 150 pounds. If we used as many warp ropes as we needed to hold the load to the yoke, there would be no slippage.    On Thursday it was raining again. I was drinking tea and thinking, Perhaps we should limit the amount of weight we put on the cantilever, if we set up an 'A' frame behind the plinth leaning backwards, at say forty-five degrees. We can lead ropes from the top of the 'A' frame to the yoke, which we will now fix near the top of the obelisk. We can then hang bags of sand from this 'A' frame, tying them off at, say, twelve inches above ground level. When we have enough bags of sand pulling the 'A' frame down, helping the weight on the cantilever to raise the obelisk, the obelisk will rise and stop when the sandbags rest on the ground. No need for packing under the obelisk, the obelisk will be perfectly balanced and we will have completed a twelve inch lift under controlled conditions.    This then, subject to the approval of the rest of the team, will be the revised cantilever plan. The great advantage of this amended plan will be perfect control and less need to restrain the cantilever weight, simply because we will be able to progressively reduce the weight on the cantilever as the obelisk rises by each twelve inch progression. By the time the obelisk has risen to perhaps seventy degrees, we will probably have unloaded much of the weight on the cantilever, perhaps leaving just the weight of the timber cantilever itself, which will easily be restrained by the friction created by the windlasses securing it to the obelisk.    Friday was dry, so while Steve and Sean continued loading the concrete blocks, I began to fill used plastic shopping  bags with sand. Although each bag weighted probably no more than 30 pounds, collectively the combined weight of sand waiting to be loaded was mounting. Sean now spotted another problem, the overhang of the cantilever box was more than the area of the box that was pressing down on the obelisk which would balance the weight of the overhang, this was straining the timbers and although the windlasses were holding, in time they were bound to break if we carried on loading more weight in this manner. In the end we decided to load the sandbags slightly further up the obelisk thus again bringing things into balance. Below is a photo of the obelisk and cantilever arrangement at this stage: << previous blog page next blog page >> To read & post comments click here return to top of this page

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