April 2014 – It begins …

Several sheets of ¾ in plywood were purchased and construction started with the fashioning of two rings,

Picture1
First arch segment cut using jigsaw

each made up of a double layer of plywood sandwiched, screwed and glued together.

Picture2
Trying out the doughnut

Care is taken to avoid end joints from overlying others. This is automatically prevented by displacing the top segments by about half their length.

The double layer of wood would provide the base support for the dome and a rail-on-castors system for enabling axial rotation of the dome.

Picture3
Staggered gluing of the segments with PVA and reinforcing with screws

The dimensions of the rings i.e. their width and radii were worked out from scaled models.

Picture4
Doughnut fixed and glued and left to dry

Having sandwiched the two layers of plywood together to form a 1½ ”  thick beam, a length of  2″ x 1″ was clamped at both ends exactly over the diameter and another shorter length pivoted through its center like the minute hand of some giant clock. To this was attached the router harness in such a way as to allow careful final trimming of the inner and outer circumferences of the ring and result in an even curve. 

Picture5
Routing the edges to a perfect circle
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