Please Explain How A Threading Dial Works.

AR. Hillbilly said:
So if I was to set the carriage anywhere on the bed and kick in the half nuts on the same line on the threading dial it will cut in the same thread? Why 29 degrees on the compound? I haven't found a manual for my lathe yet. It's a 1944 Sheldon.
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This video gave me the best explanation for why 29 deg.
Basically to cut on one flank of the groove, the compound needs to be set at 30 deg. but not a second more. However the angle can be less than 30 and not cause a problem. Because of the potential inaccuracy of a protractor on a compound, it is recommended to set it at 29 deg. to err on the side of safety.
 
I just watched that video and learned a lot. I really appreciate this. I'm going to save this video for future use. A huge thank you to each of you.
 
Charles Spencer said:
Here is a 1965 Army manual on a Sheldon 10" lathe:

http://vintagemachinery.org/pubs/2133/3556.pdf

Here are other Sheldon manuals:

http://vintagemachinery.org/mfgindex/detail.aspx?id=2133&tab=3


And here are the two manuals that most people use regardless of the brand of their lathe:

South Bend "How to Run a Lathe"
http://www.hobby-machinist.com/resources/sb-how-to-run-a-lathe-1966-27th-edition-56-pdf.2909/

Atlas "Manual of Lathe Operations"
http://vintagemachinery.org/pubs/detail.aspx?id=13891
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I belong to the Sheldon Yahoo group and have made friends with John. I also bought the book care and operation of a lathe. It has been a great help. On the links you just posted I found a manual very similar to mine and now have that saved. I do plan on buying the South Bend book how to run a lathe. I'm very much a beginner at all this but I'm also amazed at all I've learned since joining this forum. A huge Thank You to all who help others like myself.
 
Thanks for that video. That is just what I'm looking for. I like to learn why I need to do something. It seems to soak in better.
 
Bob Korves said:
The threading dial helps you engage the half nuts in the same phase that it was in before. The threading dial stays engaged with the lead screw all the time, keeping track of position while the carriage is disengaged from it. There are various rules on which lines on the threading dials can be used with which threads, read your manual. You can always use the same line each time. The threading dial on an inch lathe will not work with cutting metric threads.
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Hi Bob,
if cutting metric threads on an inch lathe and i cant use the threading dial, can i just engage the half nuts at the same line each time
or do i need to leave the half nut engaged and reverse it out?
Ron.
 
rontlz said:
Hi Bob,
if cutting metric threads on an inch lathe and i cant use the threading dial, can i just engage the half nuts at the same line each time
or do i need to leave the half nut engaged and reverse it out?
Ron.
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Different Bob, but no you positively cannot use an inch threading dial for metric threads. All inch threads repeat every inch for whole number tpi and every two inches for 1/2 integral tpi. You would have to run 127 threads on an inch lead screw to be in sync again for a metric thread.
 
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