Linking the legs
To me this is an absolute miracle how they managed to link the legs. It must have afforded extreme precision and accurate preparation. Just keep in mind that they had to build up the four legs simultaneously, working on four far distanced locations, using pre-assembled elements which in the end hat to fit with tenths of millimeters precision... they didn't have the chance to drill holes for the rivets just in place.
Even nowadays I guess would be a great challenge, although we have GPS and laser-assisted measuring instruments. AFAIK in those former times the only avaiable way was using a method called "Triangulation", calculating angles between prominent points of the landscape and therefore defining coordinates as precise as possible...
Of course (as everybody can see) they managed. An absolut great performance!
For fine tuning they used two different "tricks":
- hydraulics
- and a sandbox.
As mentioned earlier each Arbalétrier includes a hole at its bottom where some hydraulic pump had been inserted:
This gave the chance to adjust the legs some few centimeters in Z-axis:
The sandbox is attached to the scaffolding. It helps to adjust the angle of each leg:
It works like this:
Now remove the plug:
It's quite obvious to see that especially working with the sandbox affords maximum carefulness: it's a one-way trip. If too much sand flew out you can't fill it back in ;-)
But as everybody can see they succeeded... otherwise I could imagine the Tower wouldn't exist.
Let's have a closer look at some more details next.
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