The Megalith Movers Prehistoric Engineering
Blog 8th November 2015    Over the weekend I had been discussing the project with Sean at our local watering hole and we had agreed that we had a choice as we lifted the obelisk higher. Option one was to raise the height of the fulcrum as we progressed, while maintaining the present position directly under the end of the obelisk. Option two would be to move the fulcrum forward at the end of each lift. Option one would mean that each lift would be easier than the previous because the centre of gravity of the obelisk moves towards the base as the angle of the obelisk increases. The drawback is that the stability of the fulcrum would be more difficult to maintain. Option two 'moving the fulcrum forward' would mean that if we moved it too far forward the levers may be unable to withstand the weight of the sandbags needed to lift the fulcrum.    When the three of us resumed on Monday we decided to try option two and see what happened. To do this we would have to incorporate more pit-props forward of the present fulcrum position, to keep the fulcrum constantly supported from ground level as the fulcrum moved forwards. This was quickly achieved and we completed two lifts each of about one inch in the first session. After which, Sean cast his expert eye over the scaffold and quickly found two serious faults. The most serious being at one of the anchor points on the cross-braces, this had sheered completely although has Sean pointed out most of the damage had occurred long before we used the scaffold. I knew immediately from my experience with wooden cross-braces how serious this was. The offending section of scaffold would have to be replaced before we could safely continue. The other fault I was less concerned about, but bowing to Sean's superior knowledge of metal I agreed that both sections of scaffold would have to be replaced.    Tuesday, Steve and I were joined by Ewan and we quickly replaced the faulty sections of scaffold and just as quickly moved the fulcrum forward as far as it would go, which was only a matter of inches, if that. We reset the levers, reloaded the sandbags and completed another lift using less sandbags than we had used on the previous lift. So far so good. We repeated the procedure with the same result. Excellent, we were raising the obelisk without raising the fulcrum. We now had a problem. The fulcrum was now nearing the end of the scaffold (stone staircase). We could move the scaffold forward or add two more layers of timber on top of the crib, which would allow us to bring the fulcrum back to its original position of last week, under the end of the obelisk.    After having had time overnight to think about it, we decided that raising the height of the crib was probably easiest. So on Wednesday we increased the height of the crib by six inches, and whilst I was doing that Steve and Joe added more timber bracing to the scaffold. I also made a new stronger fulcrum as the old one was showing signs of stress. Finally we were ready to try another lift. I probably set the levers to high as we had a great deal of trouble loading on the sandbags as the ends of the levers were almost out of reach but slowly the obelisk began to rise. By the time we had completed the lift we had gained three inches in that one lift, our best ever result since we left ground level.    Encouraged by the success we had achieved the day before, I reset the levers hoping for another really good lift. I was probably being greedy, as I ended up setting the levers so high that we had the greatest difficulty reaching the ends and loading on the sandbags. However, after we had loaded on about on third of the bags, the rest were easier. We had just started lifting the obelisk and the sandbags still had plenty of room to travel before bottoming out on the scaffold, as we loaded on more bags the process gained speed and Steve was struggling to keep up as he adjusted the packing on the fail-safe tower. Then there was a creak, the sound of timber under strain. “What was that?” said Sean. “One of the levers I think, some of the are getting old and dry”. I replied. I had barely finished speaking when there was a loud crack, quickly followed by another and another. The obelisk came down quicker than it had gone up. “You OK Steve!”. I shouted. “Yes it's back down on the fail-safe, What happened?”. Sean replied for me. ”Fulcrum broke”. Sean had climbed forward. “Two pieces of the crib as well”.    Sean and I climbed down from the scaffold as Steve and Joe continued to consolidate the fail-safe tower. It was a disappointing end to what had been a promising day. At the inquest afterwards, Sean pointed out that we were wasting most of the energy contained in the levers just compressing the crib resulting in a limited lift. As soon as we unloaded the sandbags the crib decompressed, and we had to compress it again before the next lift could begin.    Next day, Friday, I called at the garden centre and ordered another ten of the wooden poles we were using for levers. These were probably the best levers we had ever had. Freshly cut, uniform in size, and a full three inches in diameter at the thick end. We finished replacing the broken timbers in the crib and also increased the number used, to make the crib stronger, when the new levers arrived. As I was helping the driver unload I noticed that these levers were much heavier than any we had used before. I immediately decided that I would use a length cut from one of them to replace the broken fulcrum. We still had about six good levers left and even though I had earmarked one of the new ones for the fulcrum, we now had as many as fifteen left.    Sean and myself set up the levers for our next lift, while Steve and Joe continued to strengthen the scaffold. When we were ready, Steve and Joe stationed themselves each side of the fail-safe ready to pack, and at the same time kept a watching brief on everything. We compressed the crib about two inches before the obelisk started to lift. To maintain this compression, Sean and I packed between both ends of the lifting bar and the crib. The plan then was to unload the levers and move the fulcrum forward in order to gain a full three inch lift. We unloaded the levers and the new packing held the crib compressed. It was time for a break, my old legs were becoming shaky, not good when you are on scaffold. The rest of the team had also decided it was time for a break. We were talking generally when we heard that same old sound, the sound of timber breaking, it was the lifting bar. We should have packed under the middle as well as each side. I climbed up and packed under the middle to stop it breaking further. We decided to call it a day we would start again next week. We were still learning. Below is a photo of the progress so far.   << previous blog page next blog page >> To read & post comments click here return to top of this page

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