Internal threading tool arrived but not flat?
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  1. #1
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    Default Internal threading tool arrived but not flat?

    This isn't a SB specific question but don't know where else to post. Just bought internal threading bar with insert. Bar has flats on top and bottom for registering it in my 250 series QCTH.
    Why is the insert angle not parallel to flats on bar? I was taught threading tool should be 90 deg both horizontal and vertical to centerline? With this set-up, my insert will be pointing down, maybe 10 degrees. Assume I still put the point on the centerline but then insert will have a 10 deg downward rake? Is this a quirk of internal inserts My inserts for external threading are straight in.

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    Think about the cutting edge of the insert itself. You will need to hold that insert at an angle to have the cutting edge at the proper angle. Simple as that.

    -Ron

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    OK I assumed that "they" know what they are doing but my insert is flat and when I set up the boring/threading tool bar flat, (horizontal) my insert tip has a definite downward rake of 5-8%. I am about to try it out. Just seems strange and thanks for your assurance

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    A great reason for learning grinding your own - teaches you where the clearance angles have to be.

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    I found the same issue with an cheap insert boring bar I bought recently.

    When the flats on the bar are top and bottom in the QCTP holder, the cutting corner of the insert is not on center of the part and the insert geometry is all screwed up.

    I'm not sure if it's a feature or an accident.

    For me, it kinda defeats the purpose... I wanted a small diameter bar for little holes, but when I adjust the height of the bar to get the cutter geometry correct, it reduces the diameter of hole I can work in.

    So do you have a pic of your threading holder?

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    Quote Originally Posted by Vandegraaff View Post
    OK I assumed that "they" know what they are doing but my insert is flat and when I set up the boring/threading tool bar flat, (horizontal) my insert tip has a definite downward rake of 5-8%.
    For threading, mental exercise :

    Draw a circle with quadrant lines. Put your 60* insert flat on the crosswise line.

    Except it's a thread, which is not in the same plane as your bore cross-section. So tip the insert to be at right angles to the thread.

    If you tip the back up, it will be the cutting edge because we're inside a hole. Cutting edge angles all wrong, not so good.

    So drop the front instead. Now you got what you got.

    Not perfect but should work.


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