It is made from pvc pipe including the flat PVC disks - slit a piece of PVC pipe down its length, heated in the oven and then sandwiched the softened PVC between to sheets of cement sheeting.
The mount for the torroid is a flat disk of PVC with a short length of 90mm PVC pipe glued on top - the torroid sits on top of the flat pvc disk with the PVC pipe through the center of the donut.
To the bottom of the flat disk I have glued half a small diameter PVC pipe joiner so that the whole arrangeent simply sits on top of the vertical shaft.
The vertical shaft protrudes through a hole in the top of the secondary former into the interior and can slide up and down. The other half of the PVC joiner slips over the shaft and is tight enough fitting to support the weight of the torroid. It is an easy matter to adjust the height of the torroid by moving this half joiner.
Everything is coated with epoxy resin.
The secondary coil is wound with magnet wire from a microwave oven so it is a little untidy looking. At some point I will purchase some magnet wire and wind some new ones that will look better.
I am also winding two smaller 2 inch diamater secondaries with the magnet wire I purchased to make some DIY flyback transformers. Just to compare the performance of the two sizes.