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Tool angle in the toolpost

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  • Tool angle in the toolpost

    I must have finished my 3rd book on how to run a lathe and every single one shows the old lantern post holding a "toolholder" with a bit angled up at the work piece yet everytime I see a guy actually machining stuff nowdays they are using a QCTP, turret holder or something similar. Do we take this into account when grinding toolbits? What I'm asking is, when grinding toolbits, the ones shown in the old books, show a certain amount of back and side rake yet there is even more back rate in the equation when you mount it into the old toolhoder. What gives?

    Like the old How to run a lathe book, I ground all my cutters the same yet I don't use an old toolhoder and post so the cutter engages the work at much less of an angle than shown in the books.


  • #2

    Some of those old books show tool angles that account for the holders "pointed up" position. The reason for this holder angle was that it made the HSS tool bits stronger since one didn't have to grind so deep to achieve the proper back rake. I think Armstrong holders had something like 8 degrees but even this will vary since each lathe may be a little different depending on how the holder met center. You'll need to determine the "actual" angle for your lathe. If you're grinding your bits for a flat holder - then to have the same tool cutting property as the book's - the additonal angle must be added. Some of the old books gave the angle needed, and it was up to you to subtract the angle of the holder. Double check your chart.

    One thing to remember, tool bits that have very high positive angles require much less horsepower to cut a chip. They also don't need as much rigidity in a lathe to avoid chatter. Down side, they dull faster.

    Quick-change tool holders, in my opinion, are designed for carbide tool bits that don’t need the high positive angles of HSS. I have noticed that people who make their own quick-change holders for HSS tools will angle the slot for the bit up as the old Armstrong holders did. This is especially necessary if one uses آ¼ inch HSS bits. If one uses larger bits, the angle for the holder is not quite as important since the bits are inherently stronger and will not be affected as much when the proper cutting angle is gound in.

    Personally, on the smaller lathes, I like the old post and rocker system since I can use the very inexpensive آ¼ inch HSS bits.

    Once you learn the "how" and "why" a certain bit must be shaped for the desired material and cut, it really doesn't matter what holder is available. You’ll know how to compensate for it!


    [This message has been edited by Mike Burdick (edited 01-19-2005).]


    • #3
      Thanks Mike! Since I'm about to start a project which includes 8 new toolholders for my
      QCTP I think I'll try the toolbit angle trick as I prefer the 1/4" bits myself but alas I have been using 3/8" up to this point.



      • #4
        When I made my QC tool post and holders, I compromised on 5/16" bits as my normal size. They are somewhat larger than 1/4" and therefore somewhat stronger. The price is not that much higher.

        I mount the bits horizontal and grind in whatever angle is required. I have never broken a bit but then I usually take light to medium cuts.

        Paul A.
        Paul A.
        SE Texas

        And if you look REAL close at an analog signal,
        You will find that it has discrete steps.


        • #5
          This is my own personal opinion, you can take it for what it is worth. I think the reason the old style Armstrong holders for lantern style tool posts are angled is so that when resharpening the bit you can grind all sides of the tool and still have the tool form in the same relationship to the top, side and bottom surfaces of the bit. Personally I hate lantern tool posts almost as much as I hate 3 jaw lathe chucks. No wait hate is too strong a word. Change that to dislike
          Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.


          • #6
            This is a tool holder that I made and use with good success. It does not have the acute angle of the Armstrong High Speed Tool Holders. I use it with High Speed Steel and carbide tooling as well.

            [This message has been edited by happy02 (edited 01-22-2005).]


            • #7
              On Modern Quick Change Toolholders with straight horizontal slots, you need to grind a "positive" top rake on the HS tool for the 8 degree angle.
              On the latern posts, they only had to grind the sides/front , although putting in a slanted top side relief was common.

              So what I am saying is that there is less grinding required on latern post tooling. But QC has such diversity and ridgidity, its hard for me to ever go back.

              If you want minimal grinding, use a Diamond style tool holder( not the jewel!) for HS..where only one surface of a HS bit needs to be ground,and it cuts fantastically
              Green Bay, WI