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Hello,New user to this forum, and to machining, more or less.A few years ago, when I was still working for a living, and had income, I was gathering equipment for what was to become my hobby in retirement. One of the machines I found was a 1941 South Bend 9C that appears to have been in very good condition even before someone spruced it up with new paint, etc. Anyway, from reading, lurking on sites like MEM, etc, it seemed clear that sooner or later I would need a four jaw chuck. I actually found a place online that was selling brand new Atlas 6" four jaw chucks sporting the 1.5" 8TPI specs used on my SB. When it came in, I was excited, but then pretty disappointed to find it would not thread all the way onto my spindle! I set it aside and continued to use the 3 jaw that came with the machine. But now I want to turn a shaft with an offset pin on it and I think I really need the four jaw.So, Google led me to Steamer's post about fitting a chuck to the spindle. I did not know that was 'a thing', I thought my new chuck would 'just fit'. But hey, now there is hope!I have a question on the process that was used. Early on, Steamer stated "but first we need a plug gage in the form of a dummy spindle"...Why is that? I would have guessed I could just chuck a straight bar into the 3 jaw, turn the four jaw around and clamp down on that bar, indicate on the inner bore and true things up until the new chuck was running 'true and concentric'?, and then open the bore to fit my spindle.I don't see what the dummy spindle does.Thanks for any help anyone can provide.R. G. Sheehan
The standard for 9 inch southbends and all the threaded nose Logans that I'm familiar with is 1 1/2" -8
One additional comment. While the thread may be 1-1/8 the length of the spindle nose to the registration shoulder can be different. A back plate or unitary/one piece no back plate chuck made to fit on a South Bend 1-1/8" spindle X ~ 13/16" will not fit a Logan 1-1/8" X 1" spindle. The chuck will hit/ bottom out on the spindle nose before it touches the registration shoulder because the spindle lengths are different. While it should be possible to simply cut more threads, which wouldn't change the fit to a shorter spindle nose, I can't speak from personal experience. The http://www.lathe.com/spindles.html has an informal member created list of spindles. Ron
Quote from: steamer on December 04, 2022, 07:30:53 PMThe standard for 9 inch southbends and all the threaded nose Logans that I'm familiar with is 1 1/2" -8For 40 years I had an SB "Workshop" 9 inch that had a 1-3/8" x 8 spindle. Real PITA since nothing was available off the shelf.But of course if one learns the tool a lot is possible.Gene