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Reworking a 40 taper tool

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  • Reworking a 40 taper tool

    I purchased a Taiwan made boring head for use in my Toolmaster. Ebay seller, primarily handling Asian imported tools. The language barrier resulted in my purchasing a tool with an 'ISO40' (16mm dia. / 2mm thread) adapter rather than the NMTB 40 adapter used in my mill. The seller offered a refund but I did not want to pay the return shipping costs (head is 3+" with a 40 taper adapter and 8 indexable boring bars so it's pretty heavy). And besides, I kinda like the build quality of the tool.

    So my scheme to get this tool where I can use it is to make a holder for the taper arbor so I can chuck it up in the SB9C, bore out the offending threads, and make a threaded (5/8-11) sleeve and press fit/loctite that in place. I think it should work since I do not overly torque tools into the Toolmaster spindle. I just don't think that is necessary given the size of the taper and those big drive dogs.

    So whadda ya think?
    Thanks in advance.

  • #2
    If you can get a thick enough sleeve in there it might work. If the sleeve is too thin it won't exert enough
    pressure in the hole to hold it in place. Loctite will help but if you pull the adapter in tight enough I suspect
    that it will eventually work loose. All it takes is for the adapter to come loose once to mess up the taper in
    your spindle. If there's enough room I'd make a threaded insert instead of a straight sleeve...
    Just one project too many--that's what finally got him...


    • #3
      Have you considered making a second drawbar that fits this thread? This might also give you some options in the future if other tooling with this thread become an option.

      no neat sig line
      near Salem OR


      • #4
        I did consider another drawbar. The problem with that is, the Cincinnati Toolmaster has a 'captive' toolbar. It is held inside the spindle and there is a locking fork at the top that restrains its rotation when a tool is inserted or removed. With it locked, the tool is inserted and the entire spindle is rotated until the drawbar threads engage the adapter and pulls it up into the taper. Flats on the spindle are used to snug it up with a wrench, from the bottom. There is a plate at the top of the head that is not too difficult to remove, I'm just not sure if the drawbar can be pulled out that way or not. Guess it's time to do some exploring.


        • #5
          Originally posted by LakeHouseMetals View Post
          ...make a holder for the taper arbor
          More in hope than expectation, have you checked to see if the arbor unscrews or removes from the boring head? Some are integral with the head; some are not.

          If it unscrews, it makes workholding for the modification much easier.

          Loctite needs some clearance to work so 'press fit/loctite' as a combination is not really viable.

          The page here ( says that D2 for a 40 taper is 0.935". Your thread is 0.625" major diameter, so that is the zone in which you have to make things fit.

          I would be tempted to secure a solid slug in the hole you prepare. Then cross drill and pin (secure the pin with loctite and lightly countersink and peen over the ends) before drilling and tapping for the NMTB thread.

          As it is a boring head, unless you are doing a load of back facing, all the load on the spindle will be going upwards, so nothing more than a snug drawbar is required. That is highly unlikely to cause a properly done loctite joint to fail.


          • #6
            I have some Loctite 648 on hand. From Henkel adhesives: "LOCTITE 648 is a low viscosity, high strength retaining compound with high temperature resistance. Ideal for retention of parts with a clearance or interference fit." That is why I thought it might work.

            Thanks for the link to the taper specs. That will be very useful.

            The arbor does attach to the head via a threaded joint. I'll post some pictures of the tool soon.

            Thanks again.


            • #7
              Here are some pics of the boring head.
              You may only view thumbnails in this gallery. This gallery has 5 photos.


              • #8
                Seeing from your photos that the arbor is hollow, you could remove all doubt about anything slipping by making the insert a top hat shape and inserting it from the boring head (lower) end. Even 0.5mm (0.020") of a brim on the hat would do.