Ed, Some time ago I made some adjustable hieght music stands and bought a Screw box from Seargent's Tools (remember them?), since that time I have been vaguely interested in wooden screws.
The smallest commercially made one I have is 1/2" diameter with a pitch of about 4 tpi. I thought that was a bit big for this use so I set about finding a low-cost alternative. The problem with thread forms used on metal is that they are generally so fine that wood is not strong enough to support them.
At 3/8" or 10mm I am looking for a pitch of about 3mm, I think, I keep looking. For these, after seeing a video, you-tube, where else, I used the coarsest thread I could lay my hands on, 3/8" BSW, with a pitch of about 1.5mm, not ideal but works at the low forces needed here. I took the bolt and filed a slot in it to resemble a tap, given a bit of clearance it works reasonably. The 'die' on the other hand is the tricky bit. A similar slot filed into a nut actually cuts the thread but tends to tear it, that is why I ended up using Box. The main problem is that the tap is cutting along the grain, normally, whereas the die is cutting across the grain, and we all know what problems that gives.
I am still playing. My thinking at the moment is for a Beall type cutter for the male screw. I have many thoughts about the tap but do not have acess to a metal cutting lathe so I am limited to mucking about with bits I have kicking about.
Sorry if this is more information than you were after, I do get carried away! Thanks for the comments and interest.
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