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GK1918

GK1918

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I claim to be "I am not a know it all'' but at my age this is a new one. A job came in yesterday from
the next door desal. plant I do their work. This is a 2" by 24" "0" ringed end plate that is an end
cap for one million gals of salt water. This requires (I dont know how many yet) to bore and tap
to 1/2 NP thread. So far Its set up in my lathe for a center (I stop). This being a 8-900 dollar
item I just have to do a dummy. I drilled on another lathe a piece then 1/2NPT /into tailstock,
lathe off and in back gear, no way no way no way. Must be dull, I tried in delvin no way. I go buy
a new one, that went through like butter. I measure both with screw pitch gauge, right on then
already with glasses and magnifier (no stamping on tap just 1/2npt) I find its left. Question is
what in the world is a left hand NPT tap for. This is wifes grandfather hand me down taps from
the 1920s. Its a first for me. Left hand water pipe threads????? sam
 
I've made a few parts over the years that called for left hand pipe threads. They were used in rotating assemblies and the left hand thread was needed to make sure the pipe didn't unscrew during use.
 
They also used the Left and rights to make screw in unions between to sections of pipe while doing repairs. Been a long time since I even saw a lefty tap, let alone a lefty pipe tap. That's a keeper in the "antique, and worth money" drawer.
Wheelchair Bob
 
Another possibility is to prevent connection to another type of fluid. What come to mind is the left hand threads on fuel gases in an oxy-fuel torch. I don't know if that's the case here, as I've never run across left hand NPT, but it's a thought.
 
Correct Tony, my left NPT tap is definately from the 1920s or before no local supply has never heard
of it. Just wondering if it could be for gas lights back in the day. The next hurdle was that a 1/2 NPT
requires a 45/64 drill nobodys carries that either except to order one and of course the plant needs
this yesterday so I went with 11/16 drill and that took a good two hours of hand tapping- ugh Job is done.
 
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