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Square Bits aren't Square ?

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  • Square Bits aren't Square ?

    I ground a new bit for my tangential holder and found it didn't cut properly because the angle was wrong. This holder normally is symmetrical so I can turn or face without adjusting anything but it wouldn't face with the new bit.

    After checking the usual suspects I found the bit itself was the cause - it is a parallelogram rather than a square. Measuring between the faces, the bit is the specified size (3/16" in this case) and opposite sides are parallel - but adjacent sides aren't perpendicular.

    I checked other bits, both US bits and Asian bits. While the US bits are generally better, a number of them are also not square so this seems to be a generic issue. Even from the same US manufacturer, some are square and some are parallelograms.

    While it doesn't matter for most lathe bits, it does for my tangential. Lathe bits are advertised as "square" so I assumed they were and designed the tool holder with this in mind. Worked fine with the first bit but not this one.

    Not sure what the answer is. Perhaps purchase one 3/16" bit with each order until I get another one that is square...

    Location: Newtown, CT USA

  • #2
    Could it perhaps be something with smaller size tool bits?

    I had never seen a tangential tool until just recently, so I made one to check it out. It's 5/8 shank with a 5/16/tool bit. I broached the hole and have not had any issues inserting tool bits.



    • #3

      Could it be that the company making these has found they can make more money cutting like this? I've used these for years from off shore; probably India, and have found that WHEN I knew this, it made it a lot easier to grind my tool bits to the angles I THINK I need. Bear in mind I am basically an amateur but have 36 years doing this. The capitols are there to remind myself that I handgrind my bits and they seem to work, for me at least, as good as I need. Wayne.


      • #4
        Welcome to the real world. Square tool bits aren't often close to size as a ground finish would suggest. My experience is that most are within +/- 0.002 but may go 0.002 to -0.007 AND the sides may not be the same size or very parallel. Anyone who has line bored pumps in a HBM has been bit by this snake.

        Out of square has already been mentioned.

        Lighten up . They were intended for Armstong type rocker holders with a ton of clearance and a single clamping screw.
        Last edited by Forrest Addy; 04-18-2009, 03:14 AM.


        • #5
          Perhaps you could superglue a piece of brass shim on the side that rests against the tool holder and the grinding fixture that would get you close enough to parallel till you find the bits you need.
          scariest thing to hear " I am from the government and i am here to help"


          • #6
            Inbuilt side relief if you get the right end.
            Got some here that are off to an extent of 5-7 degrees.
            I always thought it was done on purpose and never gave it a thought.

            Mind you I do use them for cutting and not as precision packing


            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


            • #7
              I notice that the Australian-made "Diamond" tool holder grips the tool by the corners, perhaps to compensate for the out-of-square-off-thickness-spec issue:


              Frank Ford


              • #8
                Tangential Tool

                What is a tangential tool used for?
                What's the advantage?
                I cut it off twice and it's still too short!


                • #9
                  It was late and I was tired when I figured this out so I was grouchier than usual. As Forrest said, bits aren't as precise as one might expect for a ground item.

                  In rechecking, the problem bit, it is about 7.5 thou different compared diagonally. Not a lot but enough so my tangential toolholder doesn't work right. I'll try AlGuy's suggestion of shimming.

                  The Mo-Max and Morse bits I checked are within a half thou diagonally so I'll try ordering those to get a bit that doesn't need shimming.

                  The tangential is my most used tool and I'd been using that same bit for 3 years so it was getting short. I guess it didn't owe me much when it made its getaway and hid in the junk under the bench. (Clumsy bastich)

                  Seastar: I use the tangential for most turning and facing because it cuts better for me than most other tools. It can turn and face without changing position on the QCTP, works well for heavy cuts moving right to left, produces a good finish on shallow cuts moving left to right. And, it is quick and easy to sharpen using the jig (which may be why it cuts so well - it is kept very sharp).

                  Last edited by GadgetBuilder; 04-18-2009, 12:35 PM.
                  Location: Newtown, CT USA