There is no real measuring, the only exception being the initial diameter of the demijohn. I used a bandsaw but any jigsaw would do.
I used the relevant safety equipment and have dust extraction, the usual disclaimers apply.
Hopefully this little gizmo will allow a stress free experience in the pursuit of cheap homemade booze. Enjoy!
Step 1: The Base
I used a circle jig, there are many many plans out there for these, this is nothing more that a slotted hole in some 12mm mdf through which a spigot protrudes. On the underside, another piece of 12mm is attached and this runs along the edge of my bandsaw table. You drill a hole roughly in the centre of the plywood off cut so that the spigot can pass through and then set the spigot to the desired radius. You keenly observant folk will have spotted that I have marked the jig graduations as the diameter, it clearly is the radius, I was having one of those days when I attacked it with a sharpie.
Any once attached, feed the ply into the bandsaw ensuring the under side fence is referenced against the table edge and when you reach the point where the spigot is parallel with the saw blade, start turning. You should end up with a lovely circle. As mentioned earlier you could use a jigsaw.
Now technically the base doesn't have to be circular because the offcut is the bit needed for the upper retention fixture. (That sounded posh)
Step 2: The Stand Sides
Using a rough guestimate I worked on 15deg as being sufficient to allow the syphon to get the wine out without the weight being too overbalanced.
I fashioned a block with a 15 degree angle and a attached the base using this block to keep it level.
The next job was to remove 2 oppostite edges of the circle. I know circles don't have edges but cut a chunk out of one and they do. I removed a maximum of 15mm at the widest point of the circle.
The bottom of the base is flush with the sides and is attached by screws.
Step 3: The Upper Retention Fixture
Once done the 15 degree block I cut earlier is used to support the upper fixture and this is eyeballed into place so that it sits above the blase in the same plane as the base (continuing the 15 degree angle) With the width of the sides being 75mm this meant the fixture supports the demijohn 75mm up fromt hr bottom. Easliy enough height to provide a steady support for a full demijohn.
Once this is screwed into place it was just a matter of tidying up the overhanging bits and giving it a quick sanding so that it would be allowed in the house.
Job done, safe removal of all valuable alcoholic content is now assured