Hiya, yeah it has been a long time since I posted that first request (more than 4 years)! Believe it or not, my internet account was not able to connect to eng-tips.com for a long long time, although a notice of each of your replies was e-mailed to me.
I got interested in spiralocks because I had heard that was one of the fundamental technologies needed to make space shuttles feasible. Everybody remembers the development of the heat-shield tiles (who can forget, now), but not a lot remember that the original rocket motors would self-destruct on the test stand due to fastener loosening, and that it was the spiralock threadform that made it work. That was way back in the 80's, I would imagine the original patents must have expired now so I wonder, why aren't more companies manufacturing Spiralock-type fasteners?
Incidentally, I would recommend Carroll Smith's "Nuts Bolts Fasteners and Plumbing" for anyone who has to deal with this type of stuff on a practical day-to-day basis.
In the end, we wound up using Nordlocks on the project from 1999 and to date no failure. The machine was running through 30 cycles per minute for minimum 8 hr shifts, naturally it has had regular service since then. I imagine each time it is serviced though, more and more nordlocks get mixed up.
About the comment of split-type lockwashers: they do work but only for small sizes, i.e. 3/8" and smaller, and I think it is because the small screws can only withstand so much stress anyway. With bigger screws they withstand bigger stresses, at which point the split lockwashers fatigue and spread, and all the preload is instantly and catastrophically lost. I remember from the oilfield days how much failure was attributable just to failure of split lockwashers, it was substantial.
