Extending drawbar thread of NMTB40 tool holders
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  1. #1
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    Default Extending drawbar thread of NMTB40 tool holders

    I run a machine shop at the local maker space where I also train basic manual machining on the mill and lathe.

    I have a new to me Summit SC EVS-550B (probably Taiwanese) CNC machine with #40 spindle, a Fagor 8040 controller and a power drawbar. I have been buying NMTB40 tool holders for it. Some used, some new. Most of the tool holders have threads that are cut 1.3 to 1.4 inches deep. Those work fine. But some of the tool holders have only 1.2 in or less of usable thread. Those do not sit securely in the machine. I have a few questions:

    1) Bad luck? While I returned the first tool holder, I picked up three more (Three Chinese and one US) with the same issue.

    2) Can I extend the tool holder thread by tapping it? I would assume I’m dealing with heat treated tool steel. What Rockwell rating are these tool holders? Do I need to anneal? I have tried doing this by hand with a three flute gun tap, and the tap chipped almost instantly.

    3) How dumb would it be to put a spacer between the tool holder and the spindle?


    Other items of note: The machine has a manual but it’s useless. Also, CAT40 tool holders don't fit. I'm not brave enough to mess with the drawbar.

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    I have the same issue with some NMTB40 holders in my Swiss Aciera F5. It happens with old-school American toolholders, so I can’t blame it on the Chinese. The holders are too hard to tap. The solutions are to stick with holders that do work, shorten the drawbar, or put a washer under the head of the drawbar. I shortened the drawbar a small amount and ditched the remaining holders that still didn’t fit.

    The holders must fit precisely in the spindle taper. The only kind of spacer that would work is a thin ground cone, which seems impractical. You cannot simply put a specter between the tool holder flange and spindle nose!


    Sent from my iPhone using Tapatalk

  3. #3
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    Quote Originally Posted by rklopp View Post
    I have the same issue with some NMTB40 holders in my Swiss Aciera F5. It happens with old-school American toolholders, so I can’t blame it on the Chinese. The holders are too hard to tap. The solutions are to stick with holders that do work, shorten the drawbar, or put a washer under the head of the drawbar. I shortened the drawbar a small amount and ditched the remaining holders that still didn’t fit.

    The holders must fit precisely in the spindle taper. The only kind of spacer that would work is a thin ground cone, which seems impractical. You cannot simply put a specter between the tool holder flange and spindle nose!


    Sent from my iPhone using Tapatalk
    Got it. So I'm not the only one. I guess I'll put these aside for now. Maybe at some point I might experiment with boring them out behind the thread (doubt that would work).

    In the mean time I'll keep looking for an ER16 NMTB40 that fits, or just a get one with a shank for the ones that do fit.


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