I think that harold's point (and I would tend to agree on this) is that under certain circumstances, the leading and trailing faces can have nearly the same loads on them, and this is the time (when the load on the leadscrew thrust bearing becomes nearly zero) when inaccurate threading can happen.
You are sure I can't change your mind?? (O:
OK then, I'll just have to settle for disagreeing.
Because Harold is a 'suspenders, belt, and duct tape too' kind of guy, he objects on what basically amounts to moral grounds, to using a less then optimal configuration.
I myself use the 30 or whatever degree infeed because I know it makes the chip flow a good deal nicer, and this seems to make the thread cutting go a good deal smoother on my older machine. There have been some times when, for space constraints, I've used direct plunge.
I myself can recall using the plunge just to get the compound out of the way.That being said I would expect most every guy who ever used a lathe has done the same. So I think everyone knows that it works.
I know that the finish produced with the plunge cut is just as good as that of the 30 degree cut, as even Harold will often plunge cut his last few passes to clean up threads, especially in 303 stainless. "When you have a sharp tool and lubricate well, the chip comes off looking like a thread, thin 60 degree chip, equally generated from each face of the thread." (that's a quote)
It seems as if the gods of the forces act uniformly depending on who's doing doing the turning. (o:
My take on the drunken thread is that it occurs ONLY as a result of the 30 degree compound being advanced in a direction opposite to the direction of threading. If you do not set the cutter direction up backward then it cannot pull itself forward and get drunk. (O:
The drunken thread cannot and does not occur using the plunge cut because the cutter is not set up to advance toward the rear. It is not being advanced into the trailing wall and does not pull itself forward. In fact the cutter has equal cutting faces and is always being forced in the direction of the cut at a rate equal to one times the pitch per revolution. All the energy required to force the cutter to advance at that rate serves to keep the carriage and half nuts well and properly seated on the lead.
In order to produce a drunken thread you would need to overcome the force required to drive the cutter forward then add the necessary force to overcome the friction, the inertia and also the additional energy needed to push the cutter forward of the intended path somehow. I just cannot see where such a force could come from.
Obviously we are all free to believe what we wish, from the evidence we can understand.
Thanks again for your views Jim.
Bill
Jim
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