1" BSP as a nut & bolt thread.

[bob ward]

I've been asked to make new pins for this bolt together crankshaft, its out of a 50 or 60 year old chaff compactor , made in Australia. The pins have a 5° total angle taper on each end, and are pulled tight into the crank throws with a nut. The threads on the pins are had me scratching my head for a while until I figured they are 1" BSP, 11 tpi.

Presumably the makers wanted to use as fine a thread as possible so that a) the pins could be pulled in as tight as possible and b) to stop the nuts loosening from vibration. When the compactor was made the only standard threads used in Australia in the 1.125"/1.25" range were BSW 7 tpi or BSF 9tpi.

Or you could think outside the box and go finer still with 1" BSP-11, quite clever I reckon.

[BobL]

Yep pretty clever.

I'm a bit of a fan of BSP threads. When I built a metal free (i.e. used lots of plastic) laboratory in the 1980's I used a lot of 3 and 6mm white poly sheet, and 1/2 & 3/4" black poly pipe and irrigation and cut hundreds of BSP threads with the set of BSP taps and dies at work. The lab walls were made of marine ply and I drilled and tapped the ply direct and clad with 3mm poly sheets using 1/2" irrigation fittings liberally coated in epoxy.

I have since inherited FILs BSP dies (1/2", 3/4", 1" and 1.5") and then purchased a set of taps and used them on pipe working, like my reticulated compressed air but also on an all aluminium chainsaw mill that I made which uses 3/4" Al tubing

[Aussie Bruce]

BSP as a standard has always had parallel threads and tapered threads / self sealing.

Parallel was always used on HD pipe for a face seal or as you have discovered when a fine thread is required on a large dia similar to M1.5 M2 M3 etc as shaft locking nuts

Bruce