Internal Threading Chart for Lathe

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I don't cut internal threads that often (usually tap), but when I do,
it takes me forever to remember how to set the lathe up correctly.
There was an excellent discussion on this topic on the Chaski Board
recently.
I made this chart which I've uploaded to the metalworking.com drop box.
Harold Vordos graciously corrected all my mistakes and as always, I
appreciate his willingness and ability to teach the craft so well.
Hopefully, this will help someone else.
George
Reply to
gglines
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What the 'L' -- you had one too many:
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Reply to
Tim Wescott
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Reply to
Ken Grunke
Threading as you suggest is not a good idea. The pressure of the cut has the ability to propel the carriage ahead of the lead screw, causing a drunken thread. Feed of the compound should *always* be in the same direction as the cut, which avoids the problem by loading the cut against the lead screw. That is, and has always been, the reason for setting the compound on different sides, depending on the nature of the thread involved.
Harold
Reply to
Harold & Susan Vordos
If I understand you correctly, you're referring to the pressure on the right side of the cutter which is taking only a minute (myNOOT) shaving? It can't be very much, if you're advancing the compound only a little for each pass as generally recommended.
Are you saying that the compound should be set at 30 degrees, instead of 29.5?
In my suggestion, the compound is *always* fed in the direction of cut, it's just set a half degree in from 30 degrees. The advancement into the left flank of the thread is so miniscule at that angle, that it barely cuts on that side.
Ken Grunke
Reply to
Ken Grunke
I'm sorry, I apologize. When I re-read your original post, I realize I misinterpreted your comments as threading from the inside to the outside (that was on my mind). *You clearly stated the opposite.* The two methods suggested are, indeed, proper, but I would hesitate to use them unless I was threading a through thread.
I would take exception to your statement about the difficulty of threading from the inside to the outside. My first attempts to do it were a result of the horrible difficulty of threading to a shoulder when chasing a 1"-8 inside thread. The bore was deep, near two inches. It was far easier to start the thread in the relief that was permitted than it was to pull the half nuts at the precise moment when threading such a course thread. I guess it's all in what one gets used to!
Harold
Reply to
Harold & Susan Vordos
Harold, I completely agree with your exception, at least when threading under power. I don't have a very big lathe (Emco Maier Compact 8) so 8 tpi is pretty big for me. For that size and for any blind hole, I thread using a crank on the outboard pulley so a carriage travel to the left into the bore isn't a problem, I can set up a carriage stop. But an 8 tpi hole can get pretty tiring after a while! :-) Thanks,
Ken Grunke
Reply to
Ken Grunke
snip---
Ah!! That's very different! I always thread under full power, including to a shoulder, internally, when it's called for. My method of keeping out of trouble is to make a pencil line on the boring bar, which is my reference to which I disengage the half nuts. It's surprisingly accurate, although when you're chasing a coarse thread it requires your undivided attention.
Not long ago I chased a three pitch auger for Susan's wheat grinder, a replacement for the original, which broke. It was made of cast iron. The auger started and ended inside a full diameter, so there was no runout. I had to pull out on one end, but the starting end I used a starting groove, a duplicate of the radius of the auger. The auger was made of 17-4PH stainless, with a left hand "thread". It's surprising how closely you can pull out when necessary. I ended up with a very nice transition from auger to straight shaft in a relatively short distance. A picture is available if you're interested.
Harold
Reply to
Harold & Susan Vordos
Can you supply a copy of the chart? I'm not able to open PDF.
Reply to
Sarah Allen
Can you supply a copy of the chart? I'm not able to open PDF.
Reply to
Sarah Allen

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