ok, so we need to make a condenser coil, now the original Boka still was a single coil, since then other distillers have found a double coil to be more effective.
a double coil is a smaller coil inside a larger coil.
ok so I had to work out how I would make the coil so that it would fit, i knew the diameter of the pipe I was using to make the coil, 6mm, and the internal diameter of the column, 50mm. the coil should be made in such a way that it fits inside the column but without touching the sides. I planned to wrap the outer coil around a pipe of 32mm copper pipe that and 6mm copper pipe x 2 = 42mm perfect.
the inner coil would then have to fit inside the PVC pipe with room to spare, the inner diameter of the PVC pipe is 30mm, so a piece of 15mm copper pipe fitted the bill, 15mm plus 6mm x 2 for the copper pipe = 27mm also perfect.
we start off by making the smaller coil, the inner coil, to do this we have to wrap the 6mm copper tube around a form, e.g. a 15mm copper pipe in my case. be careful when starting it off you need to leave enough to go out the top about 5 inches long. also when starting off take it slow, you don't want to kink the pipe, I did a little but it hasn't restricted the flow too much, if I find later it has I will have to make a new coil. when winding your coil make sure you leave a gap between turns, we want to allow the vapour to get between so it can cool on the coil.
Coil length, 8 inches in my case which is what everyone seems to say is best for this type of still, you can make it to 5 inches if you're making a smaller column but if you can make it 8 inches or more.
once the inner coil is to the length you want slide your PVC pipe over and start winding the outer coil around it when you get to the end leave 5 inch's and cut it, bend it so both ends of the coil are facing upwards using a bending spring you don't want to put a kink in it now.
you should be able to slide the copper tube out easily, the PVC pipe you may have to pull out with pliers.
check out this forum post on winding the perfect coil, click here