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- Dec 25, 2011
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The problem with the 127T gear is that on most lathes, it is much larger than the largest standard gear furnished. I haven't looked at the Logans with this in mind but on the Atlas machines made 1938 and later, the largest gear is 64T. Running a 127T may result in having to run the machine with the change gear cover open. Which is a safety no-no.
The compound gear set sold by Atlas for the purpose was 52T/44T. This results in an M1.0 being M1.0006. This isn't good enough to make precision lead or positioning screws but it's certainly close enough for normal lengths of engagement. As the thread pitch grows coarser, the absolute error increases so M7.5 nominal is actually M7.50450000. Which is where I cut off the threading chart (modified copy of the metal chart rivetted to the QCGB) that I made up for the QCGB equipped Atlas 10" and 12".
A man named Conrad Hoffman wrote a treatise on cutting metric threads on an Imperial lathe (specifically a 1947 Model 211 Logan). I have the document as a PDF but although the document isn't so marked, the home page of his web site says contents copyright 2016. So I'll merely give here the URL for the document. You can get back to the rest of his site by clicking the HOME button on the last page of the document.
www.conradhoffman.com/metricthreading.htm
The main reason that I am mentioning it here is that he describes a method whereby you can cut metric threads with an inch lead screw WITHOUT having to leave the half nuts engaged throughout the entire process.
The compound gear set sold by Atlas for the purpose was 52T/44T. This results in an M1.0 being M1.0006. This isn't good enough to make precision lead or positioning screws but it's certainly close enough for normal lengths of engagement. As the thread pitch grows coarser, the absolute error increases so M7.5 nominal is actually M7.50450000. Which is where I cut off the threading chart (modified copy of the metal chart rivetted to the QCGB) that I made up for the QCGB equipped Atlas 10" and 12".
A man named Conrad Hoffman wrote a treatise on cutting metric threads on an Imperial lathe (specifically a 1947 Model 211 Logan). I have the document as a PDF but although the document isn't so marked, the home page of his web site says contents copyright 2016. So I'll merely give here the URL for the document. You can get back to the rest of his site by clicking the HOME button on the last page of the document.
www.conradhoffman.com/metricthreading.htm
The main reason that I am mentioning it here is that he describes a method whereby you can cut metric threads with an inch lead screw WITHOUT having to leave the half nuts engaged throughout the entire process.