Technical Oddball NF(?) Thread pitch nut

There are different "classes of fit" for threads described in Machinery's Handbook. In simple terms from "erector set loose" through requiring a wrench to assemble and on to interference threads.

I see it's time for me to start thinking about getting a new edition, the 2000+ pages of my '67 Seventeenth Edition are all falling away from the binding. Hell to have to leave the traditional time frames eh?

Ed

 

Thanks for the suggestion 1940 Willys! I did try that but still couldn't start the nut. Rats! Regards, Dave.

 

Thanks wayne-o! I will break out my mics and see what they say. I did use a virgin #28 bit which was the size recommended for an 8-40 by several charts that I referenced. Regards, Dave.

 

Steve, my welder is starting to look like a possible solution! There was one brass nut behind the dimple wheel when I first took the horn apart but it was at the motor end of the threads of the armature shaft and it's hole was egg shaped. Thanks for your input! Regards, Dave.

 

Never2low: Yes, tried a #27 but still no luck. I would imagine that the contact and resulting vibration between the dimple wheel and the diaphragm would require the locknut to have a good close fit to keep the wheel adjustment from changing. Thanks for your suggestion! Regards, Dave.

 

Thanks Ed! Yes, I remember the machinists at the shipyard I worked in talking about the "classes of fit". And like your vintage handbook, I have several old reference books I've had for many years that are suffering a similar problem! Regards, Dave.

 

This is a good link that explains H limits of taps and classes of threads. The notes at the bottom are pretty good, a bit deep if you are new to threads.
http://www.tapmatic.com/tapping_questions_class_of_threads_h_limits.ydev

 

There are plenty of odd electrical threads around. I see them in screw-in electrical components often at work. Some of them do have roots that are 50+ years old.

 

Starrett has the answer. Bob

 

UPDATE: Got out my trusty vernier:. Shaft o.d.: .159 - Tap o.d.: .165.5. So according to "wayne-o" 's tip, this is a good thing and I had the thread pitch verified by a senior machinist in one of the older shops in town. This is really getting stupid! All this BS for a tiny lousy nut!! But I've been around vehicles for too long to know that this is sometimes the case. Regards, Dave.

 

Thanks muchly Bob! I will kick back and broaden my knowledge with it! Regards, Dave.

 

Wow! The "genuine Swiss army knife equivalent" of thread pitch gauges! Thanks for the pic! Regards, Dave

 

I have a few tap and die sets that come with the gauges. Mine are made by Hanson.