Al: Wonderful!and thanks
This info is a great background and a pleasant perspective. We did carefully use a half-nut and were able to eliminate the damage which was causing the problem however, given the softness of the mettle as you mention, it is likely why our method worked. Well if some "industrious" person ever manufactures thread chasers for feeder rods, they would be appreciated. Later Bob, -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Antique Phonograph List Sent: Sunday, December 21, 2014 1:07 AM To: [email protected] Subject: Re: [Phono-L] Feeder rod thread chaser inquiry Repairing threads can take several paths: The Edison 100 thread per inch feedscrew found on the Class M, Spring Motor, Triumph, and Home is an odd piece of tooled steel. When I first encountered one that needed repair I surmised that it must be a hardened steel. I was very wrong. Putting it on a Rockwell hardness tester showed that it was very soft by most standards of todays steel and was very much like ledloy 12L14, a very soft steel that is made that way to be easily machined. My first attempt for a thread chaser was a simple one. I took a nice Edison halfnut and ground down one side at an angle to make a thread chaser. It worked fairly well but had to be firmly mounted on a halfnut arm of a reproducer carriage with an adjustment for the downward pressure. Occasionally the tool would do more damage than good and I would have to scrap the feedscrew or cut a new thread after machining off the old one. I made an improved version with a twin halfnut Triumph arm where one halfnut was original and the second one was the chasing tool. It worked better but it still was not perfect. The thread depth on a 5/8ths diameter 100 thread per inch feedscrew are around 0.0064" if memory serves. In soft metal it does not take much to damage the threads beyond functional use. I haven't done so lately; but, if the mandrel and shaft is a rare one that is irreparably damaged, making a new shaft is an option for someone with machine tool skills. My last effort for making a new feedscrew on the mandrel shaft was to make a die and die holder that would cut a very nice thread on a well prepared shaft of ledloy. That took me a week and several 'rethinks' about what was not working correctly. I have purchased a dinged up mandrel with a shaft that had a good feedscrew thread. In that case you can remove the damaged mandrel and use the good feedscrew with the old, hopefully good, mandrel. I am no big fan of certain sellers on the Internet who take good machines and part them out but their donor machines have helped on a couple of my restorations. If your feedscrew is one of the very early ones with a buttress thread, you have almost no choice but to have a new one made. It took me two days just to make the cutting tool to do a buttress thread. The thread itself it could only be cut in one pass at a precise depth of 0.007". The tool lost its razor sharp edge quickly. Each use required sharpening on a surface grinder with a newly honed fine wheel. After tackling such fine threads I marvel at the ability of the Edison Phonograph Works to turn out these feedscrews in such huge numbers. Having a grandfather who was a tool and die maker along with help from many old timers in the missiles and space industry certainly helped me do the fine machining. Sadly, most of those talented machinists have left this mortal coil and the new generation I encounter today have trouble identifying which end of a screwdriver to hold. The average age of a CNC machinist today is 54! One of my mentors, Arthur Lutz, is still working at 90... Merry Christmas, Happy Hanukkah, and Seasons Greetings, Al Phonographic Curmudgeon _______________________________________________ Phono-L mailing list http://phono-l.org _______________________________________________ Phono-L mailing list http://phono-l.org
