When I first started making my boka I was continually frustrated trying to find an ok valve for a reasonable price, Ebay was order wait wait wait and find out it was crap. Trade suppliers rip cash customers blind. :angry-banghead:
Anyway had a think and came up with this:
Everything needed : Copper Tee, coupling, two bits of 12.5mm copper rod, and a stainless 6mm bolt.
Put a taper on the bolt. The slower the taper the finer the control.
Solder The copper rods into the ends of the tee
Measure the size where you want the taper to engage. Root of a 6mm bolt is about 5mm so 4.5mm is good.
Drill a hole all the way through both ends 4.5mm
continued......