Hi,
I’ve had a look through my box of old cylinder holding-down bolts, most of which have mangled hexagons from years of use and abuse. As regards length of socket-head cap screws to make some 26TPI 3/8″ Cycle thread ones from, I would be buying some 10mm metric ones at 100mm long. The other important thing to take into account is the thickness of the washer/spacer that goes under the head of the bolt. Ones in my box seem to vary enormously from 1/8″ thick up to 5/16″ !! The length of the finished bolt needs to take into account the thickness of the spacers, as you MUST not have the bolt “bottoming out” in the holes in the cylinder barrel.
I think that I may have a go at making some, and once I have turned the shanks down from 10mm to 3/8″, I will probably use my tailstock die-holder to cut the threads. With adjustable split dies I can open the die right up for the first cut, and then gradually tighten it up until the thread is a nice ‘fit’ in the holes in the barrel. As I am not a toolmaker, just an average “mechanic”, I think that will be a lot easier for me than turning the thread. My 70 years old Myford has to have the gears altered to do 26TPI, and that is too much fiddling about for me! I did some screw cutting in the lathe over 20 years ago, when I did my Motor Vehicle Engineering B-Tech, but it is but a distant blur these days, and the college lathe did not have to have the gearing changed, just a move of a lever did the job.
Brian
