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1340 Crossfeed Protractor

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Toscano

Swarf
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Apr 2, 2016
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#1
This almost sounds crazy to me if it hadn't occurred...has anyone had any problems with the degree scale on a Jet 1340 lathe? I was threading a barrel for the first time and halfway through the depth I realized a rampart thread thred was developing. Needless to say, I had to cut and start over. Before I did I rechecked everything. Although the tool post was set at 29-1/2 degrees it just didn't seem right so I applied a seperate protractor to measure it. It was Waaaay off! Set the toolpost with the seperate protractor and cut a good thread. Has anyone heard of this happening to anyone else or was it just a fluke in production?
 

Bob Korves

H-M Supporter - Sustaining Member
H-M Supporter - Sustaining Member
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#2
Compound (top) slide protractors are notorious for not being super accurate, but mostly it doesn't matter too much. You can use a precision bevel gage, a sine bar, or angle block(s) to get a more precision angle. Threading should not require a precision compound angle. You can just use the cross slide on a small thread, and you probably won't be able to tell the difference. Threading big threads is where the 29, 29-1/2, or 30 degree compound angle makes for a noticeably better thread, and any of those numbers is accurate enough. Your rampant thread may have been due to another issue, like not quite hitting the threading dial mark on one pass or the tool moving in the holder.
 
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