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  • Die cutting problem

    Can you guys please tell me why everytime i cut new threads with a die,
    The matierial bends? Even if i take a bolt with a shoulder and cut threads the whole
    Length of the bolt, the bolt looks like a boomerang?
    Last night i turned a bar down to 5mm
    To make a 5mm .8 thread stud, it was perfect until i cut the threads. Then it was bent??
    I dont know what im doing wrong.
    Thank you

  • #2
    Most cheap dies suck. Threaded bolts will have an oversized shoulder and are not to be threaded further with dies without turning them down first. The lead out might also leave a gap in the threads.

    If your dies are split dies you may also need to open them for the first pass.
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    • #3
      I'm going to guess that it's a die from one of the cheap kits as well. The dies I've got which are made by better name companies cut with a lot less torque required and cut more cleanly. If your project needs a longer thread on a screw then a better quality die is likely the answer. I recall a couple of times I needed to run a longer than usual 10-32 thread for some reason and used my Butterfield die. The results came out straight.
      Chilliwack BC, Canada

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      • #4
        Originally posted by BCRider View Post
        If your project needs a longer thread on a screw then a better quality die is likely the answer. I recall a couple of times I needed to run a longer than usual 10-32 thread for some reason and used my Butterfield die. The results came out straight.
        Or single point it. Or buy the correct sized screw.

        R.burgy: In addition to the excellent advice from Black_Moons and BCRider, I'll point out that turning the stock slightly undersize will save you a lot of grief when threading with a die. For instance, a 1/2-13 thread isn't actually 0.500 across the crests of the threads. If I was single pointing a 1/2-13 thread, I'd start with a major diameter of 0.492 or so. You can compute this yourself or use a handy-dandy online calculator like the one below.

        So, for your 5mm-0.8 stud, the rod should be turned down to 4.9 mm before attempting to thread.

        Imperial: http://theoreticalmachinist.com/Thre...dImperial.aspx

        Metric: http://www.amesweb.info/Screws/IsoMe...rewThread.aspx

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        • #5
          To add to the above, the pitch diameter does the mechanical work. Although the major diameter on a thread is important, it is less than one might think. I read a study some years ago where a group of engineers started testing major/minor diameter size vs. failure. IIRC, it was somewhere below 60% where failure began to accelerate. The inference was that there isn't much practical difference in torque limits from 65-95% thread engagement. To be clear, there was a measurable delta across the range but the slope was pretty flat.

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          • #6
            All of these are very much appreciated.
            I am a semi-retired wrench so all/ most of my hand tools are
            Snap-on. I know that most of their tools are the best bust when it
            Comes to tap/die sets im pretty sure its not theirs.
            However, Snap-on usually wont put their name on garbage.
            In the mean time i used the knowledge i learned so far and cut another
            One. A side from turning it slighty lower this time, i also cut the the threads less aggressive with ALOT
            more cutting oil to keep it cooler. Low and behold ITS STRAIGHT!!!

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            • #7
              Originally posted by R.burgy View Post
              Can you guys please tell me why everytime i cut new threads with a die,
              The matierial bends? Even if i take a bolt with a shoulder and cut threads the whole
              Length of the bolt, the bolt looks like a boomerang?
              Last night i turned a bar down to 5mm
              To make a 5mm .8 thread stud, it was perfect until i cut the threads. Then it was bent??
              I dont know what im doing wrong.
              Thank you
              Threading dies don't bend material.

              A couple things come to mind. If you're working with soft material, brass or aluminum, etc, you might be putting uneven pressure on the die holder and bending the material yourself.

              The other thought is the die may not be starting straight so the first part of the thread is not axial with your material and as you continue the die tries to self correct more axially and the result appears to be bent.

              What materials are you threading and how large are the threads?

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              • #8
                Originally posted by R.burgy View Post
                In the mean time i used the knowledge i learned so far and cut another
                One. A side from turning it slighty lower this time, i also cut the the threads less aggressive with ALOT
                more cutting oil to keep it cooler. Low and behold ITS STRAIGHT!!!
                Excellent!

                As you guessed, the Snap-On brand taps and dies are not the best. Snap-On is primarily concerned with providing high quality tools to the mechanic. In that application, it's rare that he/she needs to cut new threads. Usually they are just cleaning up threads that got messed up or rusty. If you really want high quality cutting tools, look for brands that specialize in cutting tools for the metalworking industry.

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                • #9
                  If you do not get the die started perfectly straight, weird things happen. Unless I am cleaning up existing threads I always use the die on the lathe. I have a die adapter for the tailstock. I also make sure I have a generous chamfer on the part before threading.

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                  • #10
                    Originally posted by DR View Post
                    The other thought is the die may not be starting straight so the first part of the thread is not axial with your material and as you continue the die tries to self correct more axially and the result appears to be bent.
                    This was my first thought. The die is not starting straight and as it works its way down, it's cutting more on one side, giving the illusion of being bent.
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