A typical Ordnance Survey Pillar
There is more of the pillar below the surface
not to scale
Once the location has been decided upon a 3 foot cube hole is dug and in the bottom centre is dug another 1 foot cube hole. This hole is filled with concrete and a brass bolt inserted to act as a buried mark.
When set centring marks are set up and the block & its mark covered with wood to keep it separate.
The three foot hole is now filled with concrete and a brass bolt inserted centred on the buried bolt, while the concrete is still not set angle iron anchors are inserted to anchor the pillar.
When this is set the pillar can be built, a wooden cover is put over the surface mark and the pillar shuttering erected. Cardboard sighting tubes are situated into the holes in the shuttering and the box covering the surface mark and a metal tube down the centre, a flush bracket is positioned in the shuttering.. The shuttering is now filled with concrete and tamped down ensuring that the metal tube remains upright. The brass tribrach is anchored to the top of the concrete and while it is possible centred over the surface mark. Some days later when set the shuttering is removed and any facing work completed.
The majority of pillars that we built were completed with hand mixed concrete but for the Hemswell sites we were lucky enough to borrow a cement mixer from the RAF.