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Author Topic: More TURN Threading Questions  (Read 14774 times)

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Offline Hood

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Re: More TURN Threading Questions
« Reply #30 on: August 08, 2008, 07:39:30 AM »
Thanks for the info Richm good to know the threading fix that Art did has sorted things out.
 If you were doing a G76 what infeed angle did you have?

Hood

Offline RICH

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Re: More TURN Threading Questions
« Reply #31 on: August 08, 2008, 10:57:54 AM »
Hood,
0 for radial cutting so will start with 29.5 for flank cutting.
BTW, not trying to be a purist on the measurements, info given is a whole lot better than the nut is loose or tight and for most folks they coudn't even measure the angle of the cut accurately. So I'm happy what is being cut. Will try 15, 30, 45 ( just for kicks ) on flank cutting to see how  the threads look for comparison. Will a write up on threading ( good grief don't want to do treatise on it) but thoughts are for the
newbie.
RICH

 

Offline Hood

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Re: More TURN Threading Questions
« Reply #32 on: August 08, 2008, 11:08:55 AM »
yep look forward to it.
Hood

Offline RICH

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Re: More TURN Threading Questions
« Reply #33 on: August 09, 2008, 12:39:23 PM »
Hi All,
The attached shows a comparison of some thread cutting tests. One is a radial cut and three a flank cut. All were cut using G76 with I=0, 45, 15, 29.5. So a few questions.........
1.Can you name the I used from top to bottom?
2.Which did the test nut fit on?

Here's a hint, all cut using the same tool and settings.
 :)RICH

Offline Hood

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Re: More TURN Threading Questions
« Reply #34 on: August 09, 2008, 04:59:52 PM »
I would say the third down is the only half decent one and even it doesnt look perfect, could just be because the crest has not been cut so I presume you are not using a full profile insert.
Hood

Offline Hood

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Re: More TURN Threading Questions
« Reply #35 on: August 09, 2008, 05:04:32 PM »
Oh and as far as the test nut fitting on, depends how good the testnut was ;)
 If its like some of the nuts that are available, ie some of the junk ones that come in from China (not all are junk BTW ) then its likely it fitted all. If the crest was machined on the third down then I would say that is the best thread but without seeing them in person its hard to tell from a photo.
Hood

Offline RICH

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Re: More TURN Threading Questions
« Reply #36 on: August 10, 2008, 12:48:25 AM »
Hood,
The picture was a tough one to take and the lighting was crucial as reflections disfigure the thread form.
I was curious as to how the actual cutting would turn out since I never did any flank cutting. The cutting tool was just a
sharp 60 deg. Don't have any of those fancy forming full or partial ones.
From top to bottom with comments:
45 deg flank cut - the flank side is smooth and at 30 deg and you can see the 45 deg ragged cut done on the back side
                         of the thread. But it did do a "avg" 45 deg and you can see the steps. So as expected no nut will go on
                         to that thread.
                         I think this one will really show just how well a lathe will work. Should backlash, timing, etc. be sligtly
                         off it will show up on the back side. A .001 step looks like a mountains ridge when magnified.
0 deg radial cut - the nut fit just fine. 1000 grit paper was used to clean the top edge burrs. It's probably the cleanest cut
                        thread of them all.
29.5 deg flank cut - The nut fit rather snugly. I didn't clean it up any and there was a little bit of belly on the flank side.
15 deg flank cut- The nut didn't fit on this one and you can see the difference in the thead form ( 45 deg total instead of
                         60 deg ).
I made the test nut by drilling and tapping a piece of oct shaped rod and checked it with go / no thread gage.
Hate to make generailized statements, but would quess that if a your lathe can't provide a good radialy cut thread then
you may never get a good flank cut one.
Next test should be interesting to see what happens when the spindle slows down some 25 to 50%.
One thing thats nice with CNC is that I can also duplicate a grappy thread!
RICH