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  • Thread cutting, tool holder hits tailstock center

    I am cutting a thread to a 16mm ST37 round stock using an insert type thread cutting tool. The thread is fairly long, about 100mm, so I'm using the tail stock live center to support the rod. Problem is, when starting from the far right end of the rod, the tool holder hits the cone of the live center.

    Tried to work around this by starting the thread about 20mm away from the far right end, but this means several additional steps (cut an extra groove, cut off 20mm from the end, reface the end etc).

    Then put the tool holder into the vise and used my grinder to remove material from the tip of the tool holder. This didn't help, it still hits the live center. BTW, here is the tool holder I'm talking about:



    Then I inquired about a tool holder where the insert is aligned to the right side of the holder, as opposed to the left side. Nobody has such a tool holder here...

    I then inquired about a live center whose tip is thinner so that it safely avoids the tool holder. There are such live centers, but they are categorized as "high precision CNC live centers" and are very expensive.

    I can't grind my own HSS thread cutter. If I could, I wouldn't be dealing with insert type tool holders to begin with.

    I read about a very unusual method. Basically, install the tool holder upside down and run the lathe in the opposite direction I don't know, seems too strange...

    The other option I am considering is to take one of my 2 fixed centers, put it into the lathe spindle using the MK6 to MK4 reduction and then reduce its diameter to a suitable value. I would probably sacrifice a cutter in the process, but so be it ... Beats paying lots of money for a live center that I'm going to use very rarely.

    Anybody can think about other options?
    Last edited by taydin; 07-19-2011, 06:19 PM.

  • #2
    Taydin....niether elegant,extremely accurate, or in focus, but I have been known to use this in a tight spot

    Ernie (VE7ERN)

    May the wind be always at your back

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    • #3
      Use a half dead centre.

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      • #4
        If you don't mind using a dead center, there is what is called a "half dead center". I don't have a pic, but it looks just like a regular dead center, but 1/2 of the taper is cutoff just for this type of problem. It should be common enough to find one thru a good tool supplier. Gavin beat me to it.

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        • #5
          Grinding a thread tool is not difficult. Do you have a thread gauge? I mean the flat,steel type with 60؛ notches milled into it. You just use those notches to compare your ground tool to,until you get it right.

          That big,blocky tool holder will not fit into tight spots,as you have seen. It is better for larger diameter work.

          Depending upon how critical maintaining the same diameter is on your threaded part,using the chuck option,unless it is a good,probably OLDER Jacobs chuck,or another good make, like Albrecht,can be .003" or more out,causing your thread to have a taper. Even a good old chuck will be .001" out.

          I don't think a half center would clear that bulky holder either. Could you just grind more of the right hand corner off? You might not like the idea,but the holder would still be plenty rigid without the blocky corner. You could do it neatly,and put gun bluing on the ground away area. I know the holder cost money,but a neat job would make it better for small diameter work. Still,though,the insert is pretty large for a tight spot.

          You should experiment with the idea of running the lathe backwards. Use some scrap till you figure out how it works. I have run the lathe backwards with the tool upside down when threading shallow lids. I start at the END of the cur,and thread my way OUT of the lid. It is a useful technique you need to learn.

          A good idea to invest in a CNC type center when you can. The smallest type are the little Royal centers that have a rotating center INSIDE the taper,running on needle bearings. I use one when making knurls,which is a tight job.
          Last edited by gwilson; 07-19-2011, 07:32 PM.

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          • #6
            You guys are fantastic! Thanks for all the replies. I am searching for the half dead center in local websites now...

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            • #7
              Buy a live center for a CNC lathe. They have a long thin shaft with a small center on the end for close work on the end of a shaft.
              It's only ink and paper

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              • #8
                Originally posted by gwilson
                Grinding a thread tool is not difficult. Do you have a thread gauge? I mean the flat,steel type with 60؛ notches milled into it. You just use those notches to compare your ground tool to,until you get it right.
                The tip of this insert is pointing a little down. Do I have to give this angle to a ground HSS cutter as well?


                Originally posted by gwilson
                Depending upon how critical maintaining the same diameter is on your threaded part,using the chuck option,unless it is a good,probably OLDER Jacobs chuck,or another good make, like Albrecht,can be .003" or more out,causing your thread to have a taper. Even a good old chuck will be .001" out.
                It isn't that critical really. It's a replacement threaded rod for levelling pads.

                Originally posted by gwilson
                I don't think a half center would clear that bulky holder either. Could you just grind more of the right hand corner off?
                Already tried that. I actually went to the extreme and now there is only 1mm support left for the insert. This holder is probably no good anymore.

                Originally posted by gwilson
                A good idea to invest in a CNC type center when you can. The smallest type are the little Royal centers that have a rotating center INSIDE the taper,running on needle bearings. I use one when making knurls,which is a tight job.
                I don't understand why a thinner tip live center is automatically in a separate category and so expensive. A cheap live center could as easily be made to have a thin tip. Is there anything else that's special about it?

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                • #9
                  Probably expensive because it's for CNC and it's probably built stronger for the long nose.
                  It's only ink and paper

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                  • #10
                    Just have the rod that you are going to thread longer than it needs to be ....cut the extended bit to the depth of the thread.

                    about 3/4s of an inch will do

                    then you start cutting in fresh air ..your final thread cut should just lightly scratch the extended bit.

                    you wont hit the tailstock then..and you know you're at the right depth for your final cut .

                    all the best.markj

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                    • #11
                      Originally posted by aboard_epsilon
                      Just have the rod that you are going to thread longer than it needs to be ....cut the extended bit to the depth of the thread.

                      about 3/4s of an inch will do

                      then you start cutting in fresh air ..your final thread cut should just lightly scratch the extended bit.

                      you wont hit the tailstock then..and you know you're at the right depth for your final cut .

                      all the best.markj
                      That is what I did with the first batch of 4 threaded rods. But because of a length mistake, that entire batch is now in the scrap bin. I'm trying to minimize the steps, because there is no guarantee that another oops won't happen...

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                      • #12
                        Originally posted by dockrat
                        Taydin....niether elegant,extremely accurate, or in focus, but I have been known to use this in a tight spot
                        That is very clever indeed

                        So far all dead center I was able to find locally are fully dead. I will inquire in a few shops in person and in case of no luck, this option is a solid plan B.

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                        • #13
                          Why don't you get a tool that holds the insert verticly on the left side instead of laying flat on the top? They give you more room on the sides. Or as has been said-use a tool steel bit ground to shape.


                          mark61

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                          • #14
                            Would it do to move more stock out of the chuck, set up the steady rest between the chuck and the tool and let the right end float?
                            Len

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                            • #15
                              It's a PITA but not impossible to do the threading in a couple of stages...you just have to "pick the thread up" again as you advance the shaft farther out of the chuck. It gets easier with practice...and it does help to have a good eyeball!
                              Location: Saskatoon, Saskatchewan, Canada

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