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  • #16
    Originally posted by old mart View Post
    Only a slack fit allows the nuts to run on the double male
    Oh, its probably slack, I didnt watch any videos, sounds loose from the description.

    Neat project for sure. I like it. JR

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    • #17
      From watching the video, the nuts seem to be a reasonably close fit- more so than regular nuts. There is a clear cut path for threads of either turn, the only difference now is that the flank of the thread is no longer a full area of contact- it has been reduced to a series of triangle shaped lands. The weight carrying capacity is sharply reduced- but it seems obvious that a nut of either sex will run on it, and with fair precision.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #18
        Originally posted by darryl View Post
        From watching the video, the nuts seem to be a reasonably close fit- more so than regular nuts. There is a clear cut path for threads of either turn, the only difference now is that the flank of the thread is no longer a full area of contact- it has been reduced to a series of triangle shaped lands. The weight carrying capacity is sharply reduced- but it seems obvious that a nut of either sex will run on it, and with fair precision.
        Hence, Acme. JR

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        • #19
          Nobody has worked out the answer to my post #15 yet, it's only a matter of time. Don't overcomplicate your thoughts by thinking in terms of right and left handed threads, think more on how the threads were produced.
          Last edited by old mart; 12-18-2020, 10:36 AM.

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          • #20
            A bolt like that with a left hand nut and a right hand lock nut would be a "head scratcher" for someone trying do disassemble 😁
            Helder Ferreira
            Setubal, Portugal

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            • #21
              Originally posted by old mart View Post
              Nobody has worked out the answer to my post #15 yet, it's only a matter of time. Don't overcomplicate your thoughts by thinking in terms of right and left handed threads, think more on how the threads were produced.
              The helix angle is so steep it can't stay tight:
              Helder Ferreira
              Setubal, Portugal

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              • #22
                Thats it, Noitoen, the helix angle. Cutting the male thread with a router is actually producing a 60 degree thread no matter what the helix angle is. The cutter is three dimensional, cutting around the diameter to form a groove will give a 60 degree groove. Cutting longitudinally will also give a 60 degree groove. Not so with a conventional threading tool, the cutting edge is two dimensional and will cut a simple groove with the same angle as the cutter. As the helix angle increases, the angle of the groove (thread) gets less. I am assuming that there will always be enough tool relief that rubbing never occurs. The tool could be tilted to equal the helix angle and would then cut a true thread angle, but to produce both right and left hand threads, two tools would have to be used with opposite tilts. I did not notice anything special about the internal threading tool used in the video.

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                • #23
                  If the nut was also cut with left and right hand threads would you have a Schrödinger's nut? It can be loosened and tightened at the same time.

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                  • #24
                    Originally posted by old mart View Post
                    Thats it, Noitoen, the helix angle. Cutting the male thread with a router is actually producing a 60 degree thread no matter what the helix angle is. The cutter is three dimensional, cutting around the diameter to form a groove will give a 60 degree groove. Cutting longitudinally will also give a 60 degree groove. Not so with a conventional threading tool, the cutting edge is two dimensional and will cut a simple groove with the same angle as the cutter. As the helix angle increases, the angle of the groove (thread) gets less. I am assuming that there will always be enough tool relief that rubbing never occurs. The tool could be tilted to equal the helix angle and would then cut a true thread angle, but to produce both right and left hand threads, two tools would have to be used with opposite tilts. I did not notice anything special about the internal threading tool used in the video.
                    I don't think so... The included angle of a thread is always measured on centerline and parallel or rather square to the workpiece axis of rotation - not inline with the helix angle. The router will cut on centerline as long as it's positioned correctly, just like the single point tool. 60° is 60°... Or whatever angle he used. If the router bit and the single point threading tool are ground to the same angle, they will cut a close-fitting mating thread. If you cut that shaft in half and measure at centerline, you still have a 60° included angle - it's physically impossible for it not to be if the tool is ground at 60°.

                    The angle of the tool doesn't change just because a thread has a steeper helix angle... The single point tool should still be flat on top to maintain an accurate included angle - you don't generally change the top rake angle on a threading tool for larger pitch, only side clearance angles. In extreme cases, the top rake angle can be altered - but in that case the tool's included angle must be reground so that the included angle formed by the tool is still dimensionally accurate at centerline and square to the axis of rotation. This involves compound angles and is a large pain in the you-know-what without something like a tool and cutter grinder.

                    Your reasoning about tilting the tools is exactly why it is not done that way. The included angle is measured square with centerline/axis of rotation and not aligned to the helix angle for that very reason.

                    The router bit may alter the included angle slightly at high helix angles, I'll give you that one. But I think it wouldn't be a lot, and probably inconsequential for the most part until it gets to a helix angle over at least 30°. The relief angle of the tool must be greater than the lead angle of the thread to prevent that. That is why, for external thread milling a tool is generally used that is like a side milling cutter from a horizontal mill, and the spindle of the machine is sometimes kicked to match the helix angle. Otherwise you need excessive clearance angles on the tool. This does necessitate a different included angle on the tool though.

                    It's a complicated subject. Suffices to say that on relatively low helix angles it's not that much of a difference - might well fall within thread tolerance. On very high helix angles it could be a problem.
                    Last edited by eKretz; 12-18-2020, 03:32 PM.

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                    • #25
                      Measuring the thread will show the angle as you say, but as the threads are produced by completely different methods they will never match. The thread as produced by the router will always have an angle of 60 degrees, but will not measure the same as a 60 degree thread gauge placed on it on the centre line and in line with the axis.
                      The internal threads will both measure 60 degrees using a thread gauge.
                      Last edited by old mart; 12-18-2020, 03:30 PM.

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                      • #26
                        Originally posted by old mart View Post
                        Measuring the thread will show the angle as you say, but as the threads are produced by completely different methods they will never match. The thread as produced by the router will always have an angle of 60 degrees, but will not measure the same as a 60 degree thread gauge placed on it on the centre line and in line with the axis.
                        The internal threads will both measure 60 degrees using a thread gauge.
                        Yes I think I misunderstood your other post - you are saying that centerline angle will be good but the angle measured inline with the lead angle will be different, yes? That is so but as I mentioned, at lower helix angles it should be close enough not to matter. As the lead angle increases there will be a larger and larger mismatch. Not sure where the crossover point is where that might begin to cause a problem.

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                        • #27
                          Originally posted by dian View Post
                          who can think of a practical application?
                          Axelson lathes used a right and left helix scrolls on their rapid travel shafts. It was a much faster rate, probably something like one turn in 4 inches (approx.).

                          Sarge41

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                          • #28
                            The difference between the thread profiles is very large because the 4mm pitch thread has 10 starts, and even on that large diameter the helix angle is pronounced. My post #22 was probably missleading because it was back to front.

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                            • #29
                              Originally posted by eKretz View Post

                              I don't think so... The included angle of a thread is always measured on centerline and parallel or rather square to the workpiece axis of rotation - not inline with the helix angle. The router will cut on centerline as long as it's positioned correctly, just like the single point tool. 60° is 60°... Or whatever angle he used. If the router bit and the single point threading tool are ground to the same angle, they will cut a close-fitting mating thread. If you cut that shaft in half and measure at centerline, you still have a 60° included angle - it's physically impossible for it not to be if the tool is ground at 60°.

                              The angle of the tool doesn't change just because a thread has a steeper helix angle... The single point tool should still be flat on top to maintain an accurate included angle - you don't generally change the top rake angle on a threading tool for larger pitch, only side clearance angles. In extreme cases, the top rake angle can be altered - but in that case the tool's included angle must be reground so that the included angle formed by the tool is still dimensionally accurate at centerline and square to the axis of rotation. This involves compound angles and is a large pain in the you-know-what without something like a tool and cutter grinder.

                              Your reasoning about tilting the tools is exactly why it is not done that way. The included angle is measured square with centerline/axis of rotation and not aligned to the helix angle for that very reason.

                              The router bit may alter the included angle slightly at high helix angles, I'll give you that one. But I think it wouldn't be a lot, and probably inconsequential for the most part until it gets to a helix angle over at least 30°. The relief angle of the tool must be greater than the lead angle of the thread to prevent that. That is why, for external thread milling a tool is generally used that is like a side milling cutter from a horizontal mill, and the spindle of the machine is sometimes kicked to match the helix angle. Otherwise you need excessive clearance angles on the tool. This does necessitate a different included angle on the tool though.

                              It's a complicated subject. Suffices to say that on relatively low helix angles it's not that much of a difference - might well fall within thread tolerance. On very high helix angles it could be a problem.
                              interesting. so if i tilt the round shank cutter in the holder im not producing threads to specs? i would have to use a 60°+ point? and all the inserts that get shimmed? are they larger than 60°?

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                              • #30
                                A guess, here, but I think the helix angle on the Russian's thread is about 17 degrees. As an example of the angle changing, you can cut a piece of card and fit it into a vee block Now rotate the card and watch the angle of the gap change. If you had a cone with a 90 degree end and fitted it in the vee block, it would still fit if it was rotated.

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