On Monday 16 July 2012 09:10:43 andy pugh did opine: > On 16 July 2012 10:27, Gene Heskett <[email protected]> wrote: > > No 7mm by anything, and that is the size I'll have to use for the > > larger section > > I have never seen a 7mm screw.
I got to wondering about that. Its marked 7mm, but I'll measure it, it does look bigger to me too, but my eyeballs have seemed to be out of calibration of late. > I did once see a 9mm nut. > You almost never see the "2nd choice" sizes in the table here: > http://en.wikipedia.org/wiki/ISO_metric_screw_thread > with the exception of 3.5 which is used in electrical wall-boxes. > And Bugattis. Humm, my calculations for the care and feeding of G76 might stand some tweaking. I was desirous of a nearly interference fit in the 1/4-28 thread I was cutting when I wrote that wrapper, and I seem to have achieved that goal in that I've not seen any great evidence of powder gas coming through the thread clearance yet. The actual high pressure seal is beyond the threads. I added that step to the machining of the #209 nipple precisely to concentrate the forces of metal to metal contact and achieve a better seal as the OEM version didn't have that concentrator. But the threads are also well greased with an anti-seize, so it may be that the grease is trapped by the seal ridge and powder gas, even at 20kpsi, has no place to go. That BTW is one of the designed in problems with inline ignition black power weapons. If the front face of the breech plug or its seating surface in the barrel, has become gas cut, allowing gas to blow past and into the threaded area, the gas pressure against the thread thinned end of the barrel might get high enough the barrel banana peels forward off the plug. One maker claims his can use true smokeless powder, but several who have, with its 50 to 60 kpsi pressures have had it do just that, with severe damages to the hand holding the rifle being the result. The designer of that action gave the maker a good, safe design. But when it went into production, the tap was changed from a bottoming tap to the usual tapered nose tap, and the threads on the breech plug were rebated because of the tap change "to ease manufacturing". But that left the front of the breech plug unsupported by the missing 3 threads. At 50kpsi, the barrel stretches a micron or 2, the breech plug also compresses, so that metal to metal contact for a seal at the front of the breech plug becomes a gap, and full gas pressure is allowed into the gap in front of the threaded region. Then to paraphrase the concrete question, it is not will it crack, but when. That is precisely why most modern BP rifles carry a huge red headline at the top of every page of the owners manual that smokeless powders are absolutely verboten. But every generation it seems has its quota of idiots that can rise high enough up the food chain to make a decision that gets his fellow man injured or killed. :( For us in this side of the pond, that wall plate screw is #6-32 and very sloppily made. If I need a screw that size, I can easily buy them far better made at Tractor Supply. I would have hoped that Bugatti called for a higher quality of screw. ;-) Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! Oregano, n.: The ancient Italian art of pizza folding. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
