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  • Chasing A Hardened Thread

    After going through all the time to thread the mounted points to fit my internal grinding arbor I found out that the arbor doesn't want to seat in the T&C grinders quill.

    I've never used this 1/4"-28 internally threaded arbor because I couldn't find any wheels with that size threaded shank. (see my other post)

    The the thread on the arbors is 3/8"-24. The one smaller arbor that takes the 5/40 threaded point screws into the quill and seats, it's a little tight just before it seats but it seats and centers OK.

    The other arbor tightens up but is centering on the threads and not seating on the taper.

    I checked the seating depth of all the arbors using an adapter busing. They all seat exactly the same depth, so it's not the thread bottoming out in the quill. The OD of the threads all measure the same, so it's all in the thread cut.

    To further prove this I threaded the regular wheel arbor screw in a die, it went through with no resistance but the other two arbors start in the die but won't go far, a couple turns. That's where the problem is.
    So....... it seems like my only option is to chase the threads on the arbor but HSS won't do it. Do they make carbide dies???? I'm not even sure carbide will cut them.

    I don't like the idea of a taper tightening up by turning into a matching taper, not a great design in my opinion but no other way to do it.
    The threads should be loose enough to allow the taper to seat.

    JL..............

    Last edited by JoeLee; 06-29-2018, 12:30 PM.

  • #2
    Lap it with a brass nut and fine lapping compound. A sharp triangular hard Arkansas stone will also work.

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    • #3
      If the thread fit is best a little loose, why not rotate them slowly, and chase them with a small hand held triangular diamond file?

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      • #4
        The thread is not loose..... it's tight. The OD measures right. The thread isn't cut deep enough. A file won't cut it either plus it's a fine thread.

        JL...................

        Comment


        • #5
          Originally posted by JoeLee View Post
          The thread is not loose..... it's tight. The OD measures right. The thread isn't cut deep enough. A file won't cut it either plus it's a fine thread.

          JL...................
          You mean it's an internal thread and the ID is correct? How truncated do you think the internal crests look? Meaning, how shallow was the thread cut, in thousandths? suppose you take some 1/4-28 bolts and, using an adjustable die, reduce their diameter a few thousandths, just to see what it takes to get a good fit? If not much is needed, you could more easily reduce the external threads you just put on the arbors to get them to fit.

          Comment


          • #6
            Originally posted by CreakyOne View Post
            You mean it's an internal thread and the ID is correct? How truncated do you think the internal crests look? Meaning, how shallow was the thread cut, in thousandths? suppose you take some 1/4-28 bolts and, using an adjustable die, reduce their diameter a few thousandths, just to see what it takes to get a good fit? If not much is needed, you could more easily reduce the external threads you just put on the arbors to get them to fit.
            No, It's the thread on the end of the two arbors pictured.
            The OD is correct. The threads are not cut deep enough on these two. Real tight screwing into the quill.

            JL................

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            • #7
              OD doesn’t matter; it’s the Pitch Diameter that counts. Pull out your thread wires and check if the PD is within spec. It likely isn’t.

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              • #8
                Originally posted by bobm4360 View Post
                Lap it with a brass nut and fine lapping compound. A sharp triangular hard Arkansas stone will also work.
                This. Best way to loosen up a hardened thread is to lap it, and that doesn't take very long.

                Comment


                • #9
                  Can’t you get it ground?, ive sent threaded components for grinding several times, ok not cheap btw, but it will give a very precise thread, like plug gauges and such, lapping sounds like a solution, diamond in a brass or Ali split nut? Like a split die perhaps
                  Mark

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                  • #10
                    Originally posted by adatesman View Post
                    OD doesn’t matter; it’s the Pitch Diameter that counts. Pull out your thread wires and check if the PD is within spec. It likely isn’t.
                    Your right, the OD doesn't matter as long as it's within spec. The OD on these three arbors are ground so the thread tops have a slight flat to them. They all measure .365.

                    Here is a better picture. Using the hex die as a go - no go gage, you can see that it threads down the screw of the original wheel arbor with no resistance. It won't thread down the other arbors, I can just start it a couple turns. That tells it all.
                    I have a full profile insert that I can use if I can set these up in the lathe and line up the thread so it tracks.
                    I think the carbide will cut it, I can remove material with a file.

                    This is one instance where you need a loose fitting thread, and extra loose won't hurt. You need to be able to feel when the taper seats, as of now I can't.

                    I don't like the idea of lapping because you don't know what your lapping or how it's going to turn out. I could end up with sloppy rounded worn looking threads and still no fit.

                    JL.................

                    Last edited by JoeLee; 06-29-2018, 04:48 PM.

                    Comment


                    • #11
                      Sorry, you misread my #3 post, I meant that if the fit you require is a little loose, ie, a smaller male thread is required, then put the shank in the lathe as for threading and use one of those tiny triangular diamond files to chase the thread. With back gear and lowest speed, it can be done by hand over short selected areas. Some of the half round ones have tight rads.

                      Comment


                      • #12
                        Originally posted by JoeLee View Post
                        Your right, the OD doesn't matter as long as it's within spec. The OD on these three arbors are ground so the thread tops have a slight flat to them. They all measure .365.

                        Here is a better picture. Using the hex die as a go - no go gage, you can see that it threads down the screw of the original wheel arbor with no resistance. It won't thread down the other arbors, I can just start it a couple turns. That tells it all.
                        I have a full profile insert that I can use if I can set these up in the lathe and line up the thread so it tracks.
                        I think the carbide will cut it, I can remove material with a file.

                        This is one instance where you need a loose fitting thread, and extra loose won't hurt. You need to be able to feel when the taper seats, as of now I can't.

                        I don't like the idea of lapping because you don't know what your lapping or how it's going to turn out. I could end up with sloppy rounded worn looking threads and still no fit.

                        JL.................

                        I've always heard that if a file would cut the material, HHS would also so if the die you tried is slightly dull, perhaps that's why it doesn't work for you. If that's the case, perhaps a good quality brand new HSS die will bring joy to your life.
                        Location: Saskatoon, Saskatchewan, Canada

                        Comment


                        • #13
                          Originally posted by old mart View Post
                          Sorry, you misread my #3 post, I meant that if the fit you require is a little loose, ie, a smaller male thread is required, then put the shank in the lathe as for threading and use one of those tiny triangular diamond files to chase the thread. With back gear and lowest speed, it can be done by hand over short selected areas. Some of the half round ones have tight rads.
                          I would give that a try if I had any of those files. I'll have to look into it, but 24 pitch thread is pretty fine. It would have to be a thin file.
                          I have some small pattern files in various shapes but even the thinnest one won't fit the thread pitch.

                          I don't think a knife file like this is thin enough to do the job on this thread. It says 1/16" thick. It doesn't say weather that is the thick edge or the thin edge.
                          https://www.mcmaster.com/#diamond-files/=1di0ml0

                          JL..............
                          Last edited by JoeLee; 06-29-2018, 06:21 PM.

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                          • #14
                            A lot of threads here are hard to follow

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                            • #15
                              Get a Dremel Grinder and mount a cutoff wheel that has been dressed on a pedistal grinder to give you a 60 degree profile.
                              Then mount it on the lathe and chase the threads.

                              Rich
                              Green Bay, WI

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