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Question - Boring on a lathe

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  • #31
    He is getting a smaller hole at the end of the bore. If the problem was the tool heating up, it would be larger.

    If the work was heating up, the hole would be smaller when it cooled and contracted.

    1.25" ID, 3.6" long, the hole is several thousanths smaller at the end, AND COOLING reduced the taper. Sounds like an expansion problem in the work piece.

    1. Tool is slightly dull producing excessive heat while cutting. DO CHECK IT.

    2. Tool is rubbing, again producing excessive heat.

    3. Tool is being used at incorrect rake angle, again producing excessive heat.

    4. Cut is too agressive. You could try a slower feed or shallower depth of cut.

    5. No or too little coolant. You could try more coolant.

    I have seen videos of the fancy CNC equipment and they seem to use a lot of flood coolant. I suspect this is mostly to control the temperature of the work piece to avoid expansion and the errors associated with it.
    Paul A.
    SE Texas

    Make it fit.
    You can't win and there is a penalty for trying!


    • #32
      I DO realize that. I was just pointing out things that most dont think of when trying to bore to a size and have problems. Same thing will happen with a boring bar on a mill. Jim

      Ps. Alot of people are using these inserted bars but arent running them anywhere close to the required speed for the carbide to perform correctly.


      • #33
        Originally posted by hwingo
        The boring bar has the following nomenclature:

        NBS_12 3/4 x 10" INTRNL TRNNG TL/HLD

        and the insert has the following nomenclature:


        Well, I'm confused!

        The bar nomenclature above seems to be more of a manufacturers part number or designation sot it does not tell me much.

        As for the flat on the top of the bar, it usually indicates the index angle of the bar as if it were mounted in a boring head or turning tool holder, the screw securing the bar would press against the flat, so in this case the flat would (should) be horizontal.

        As for the insert being a TPGC, the C designates that the mounting hole is countersunk on both sides. I'm not sure that there is such an animal as a TPGC since a TPG should have 11° relief angle so there is no reason why you would want to be able to install the insert upside down, so there is no need for the hole to be countersunk on both sides. The insert in the picture shows what appears to be 0° relief, so the insert in the pic looks to me more like a TNGC,(just guessing) which would make sense, as you would be able to use all six points on it since it is a negative insert. I'm guessing that the correct insert for that bar is a TPGB 321 which would be 11° relief, with a hole, and countersunk on one side. The bar would be rotated so the insert and flat on the bar would be horizontal and the cutting edge on center of the bore, and the insert would have the necessary relief so it would not drag or heel.

        May be perfectly wrong since I'm not an insert wizzard, but that's my take on it anyway!

        Last edited by Glenn Wegman; 05-17-2009, 05:58 PM.