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Yet another cool toolblock:

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  • Yet another cool toolblock:

    Picked up some TNMC 4xx carbide inserts and managed to finish up another one of my toolblocks. The TNMC is a triangular threading tool that sits in the holder vertically, rather than flat, so the "pocket" is on the side of the holder.



    Again, the tool height is fixed with these, so I made another solid stop. These particular ones are zero rake, but the same insert is available in 5 degree and 10 degree built in. So with a "level" pocket, I can vary the rake just by changing inserts.

    The brunt of the cutting force is on the walls of the pocket, the button-head machine screw is just to hold it in place. That's about as low-profile as I can get for cutting to a shoulder, if I need to.

    Here's a close-up of the tool in the pocket:



    There's plenty of "stick out" to the insert and clearance to the block, to make some pretty mongo threads. Probably bigger than I can actually do on this little 3/4HP 11" lathe.

    I also picked up some trapezoidal CNMG type inserts (double sided negative rake) for the fourth and last block. Time, however, is as usual against me.

    Doc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    Doc,
    Nice work.

    I had thought about putting about 8 or 12 of these around a circular disk and running them from a geared motor mounted on the crosslide to make a poor mans thread milling attachment.

    I know it's been done before but I've never seen an inserted cutter.
    At least using these you aren't limited y revs.

    John S.
    .

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



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    • #3
      Doc, hopefully with these you won't have the problems I have had with threading inserts in the past. The small ones can be very fragile and if your are not running into a relief groove at the back they are suseptible(sp) to breakage if you over shoot the back of the thread
      Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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      • #4
        Spin- Considering that the insert is pretty huge, comparatively (1/2" IC, overall OD of the triangle is about the size of a quarter) and the lathe is a relatively small 11" with a cone-pulley belt drive, I suspect I'd have to work pretty hard to badly damage an insert.

        But we'll see.

        John- Eight or twelve? How big a wheel do you need? For something like that, I'd look more at those "Thinbit" inserts- cheaper per insert, and you could get more on a wheel.

        Just make sure you have a skookum blade guard on that puppy!

        Doc.
        Doc's Machine. (Probably not what you expect.)

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        • #5
          Doc, That holder is to die for !

          Spin, I've had some problems with small Thinbit threading inserts and have to use a relief groove with them. They will not tolerate the tip digging in much.

          Den

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          • #6
            nheng, that's why I almost always use HSS for threading. There are two exceptions and that is in a Hardinge Tool Room lathe or a CNC where the tool pull-out is controlled by the machine. But with carbide threading inserts I always plunge straight in as it helps to keep the cutting forces split evenly between the two sides
            Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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