I just realized I never uploaded pics of mine to the interwebs (i'll have to get on that tonight...).
View of False bottom
Generic top view of mashtun
Here's a picture of my hand drawn design of the bottom drain; the very top and very bottom images are my sketches of the 1 1/2" tri clamp ferrule option and the middle (option 2) drawing was when I was considering welding in a camlock fitting as a bottom drain (I'm glad I went with the tri clamp; for the record).
I'm using a 13.2 gallon double walled, insulated stainless mashtun. It's made by a German/French company who sells them through their Ebay Germany store; they refuse to ship directly to the US, though so you need a european intermediary to ship through. (I lived in Ireland so I got lucky.)
The picture isn't mine but one that is very much similar to mine. I had a bottom draining 1 1/2" triclamp fitting welded in, unlike the weldless fitting in the picture.
The false bottom was simply a sheet of perforated 304 stainless 0.06" thick with 0.09375" diameter holes and a 0.15625 close stagger (16x16") -we then cut it into a circle with a plasma cutter and ground it down on a bench grinder to get it to fit. I then just used stainless bolts and nuts to stand it off of the bottom slightly less than 1/2".
It results in a 1:1 height to width ratio for 10 gallon mashes (no stuck mashes for me even while constantly recirculating at a pretty good speed) and a 1:2 height to width ratio for 5 gallon mashes. (Slightly cloudy wort but REALLY fast and stick-free mashes.)
It definitely smoked a lot while welding it as the heat started burning the insulation inside; my welder didn't really know what he was doing and getting a hole big enough into this thing was a HUGE PITA as it wouldn't fit on a drill press...
It holds temp like nobody's business.
I designed it for brain-dead english style single infusion mashes and with the idea that I'd want to eventually move to HERMS. The insulation means that all the heat I get from my HERMS coil goes to quickly ramping up my temp (very little lost heat) and the high width to height ratio means that I don't have to worry about getting a stuck mash; being able to recirculate at a faster rate means that the liquid comes out of the HERMS coil at a lower temp and doesn't damage my enzymes as much while they're at their hottest either.
VERY happy with my design and equipment; but very unhappy with my welder.
Adam