Single point cutting at 60 degree compound.

Now I get it! Sorry that was so painful. I'll sleep better. This has been bugging me for a week.
Thankyou very much. Peace out
 
The idea behind advancing at an angle is so that the brunt of the cutting is done by the leading edge of the tool, the part advancing into the work.Plunging can lead to more drag and chatter. I plunge fine threads, say 20 tpi and up. Angle cut the courser ones.

Say you have a 2 foot by 2 foot hole in the ground. Now you want to make it 4 foot by 4 foot. Does it matter whether you tale 1 foot off of each wall, or just gouge 2 feet of the North and east walls? The hole will be the same in the end. Yes, it's position will move a bit, if it matters. In threading most times the position doesn't matter. You are cutting from the end to some set point. By coming in at an angle, you do advance the thread at that instant diameter down a bit, but all the really means is the thread moves around the circumference.
 
Most hobbiests will either end in a groove or let the tool cut a groove at the stopping point of the thread. If you stop early or late then the groove will get wider but not the thread because you are following the flank of the too bit as you go deeper. I do not use a groove to end the thread as it creates a stress riser and weakens the fastener.
 
BtoVin83 said:
Most hobbiests will either end in a groove or let the tool cut a groove at the stopping point of the thread. If you stop early or late then the groove will get wider but not the thread because you are following the flank of the too bit as you go deeper. I do not use a groove to end the thread as it creates a stress riser and weakens the fastener.
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My understanding has been that a thread relief (groove), being only 0.002-0.005" deeper than the Minor Diameter, does not appreciably weaken the part. A thread relief is a common feature in many turned threaded parts in the industry and not just hobby guy parts, although admittedly not common in mass produced fasteners that are not single-pointed. My question is how significant a stress riser and weakening feature is a thread relief? Is there a source I can look at to guide me in this? I've been threading parts for 30 years and have never had a part fail at the thread relief but that doesn't mean it can't happen so I want to learn more about this.
 
My experience comes from oilfield related machining and I cannot recall any oilfield application where a relief groove was allowed. I have made draw works shafts that could not have any sharp shoulders or keyways. All diameter transitions were large radius and gradual changes. Even the sprockets we shrunk on the shafts had special tapers so as to relieve the stress at the faces of the sprocket hubs. When you have hundreds of thousand pounds suspended above a hole in the earth you had better have it right.
 
I can certainly see how drills that go thousands of feet into the earth have to sustain very high loads so it makes sense to be very strict re stress risers in that situation. Thanks for clarifying.
 
My experience has been similar to mikeys. None of the times a relief groove was used for cutting to a shoulder did it result in a failure. Not to say that relief grooves are always OK. It depends on the application.
As a hobbyist, we generally know very little about the stresses in the parts we make and what our safety margins are. So it becomes difficult to choose which of the specialized applications in industry we should blindly follow, if any.
 
Tozguy said:
My experience has been similar to mikeys. None of the times a relief groove was used for cutting to a shoulder did it result in a failure. Not to say that relief grooves are always OK. It depends on the application.
As a hobbyist, we generally know very little about the stresses in the parts we make and what our safety margins are. So it becomes difficult to choose which of the specialized applications in industry we should blindly follow, if any.
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Yeah although we are comparing oil rigging and drilling to steam engine and hobby shop fasteners the same principles apply when it comes to stress and strain. The difference being that stress risers really, really matter in the field and are really, really insignificant for the hobbyist. Until it isn’t - but that is a matter of knowing how much tension your fastener will be subjected to and then sizing the diameter and creating stress risers to compensate.

Hobbyists are primarily going to use relief grooves for clearance and ease of machining, not for stress reduction in the part.


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Todd Adams said:
I haven't received my new lathe yet, but have been studying every nite in preperation.
If you set the compound at 60 degrees and advance the compound on every cut, wouldn't that position the cutting tool closer to the chuck creating a wider valley every time you go deeper? I'm missing something. I would think you would want to go parallel with the chuck, straight in. Confused.
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Believing the compound rest to cross slide numbers cut into the lathe does not necessarily give you that number in the completed part, sometimes by much more than you might guess. Be careful about the "measure it with a micrometer, mark it with a crayon, and cut it off with an axe" approach that we often use unintentionally, because we believe too many scales at face value. Trust, but first verify...
 
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