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  • Carbide insert angle

    Good afternoon ye gentlemen of vast machining knowledge and experience. I've been a lurker here for quite some time and really enjoy learning from you fellows!

    I'm building a ball turner attachment very much like the one Steve Bedair shows on his site at http://bedair.org/Ball/ball3.html A friend gave me a couple of small triangle shaped carbide inserts that fit an Aamco brake lathe. I'm going to use them since they were free. They don't have any clearance/relief angle. Do I just mill an angle into the toolholder so the insert tilts "down" at the nose about 5 degrees or so?
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    The pictures in the link you posted showed a positive insert. They have their socket machined flat with the rest of the holder.

    If the inserts you have have no relief in them they are negative inserts. I think most negative insert holders sockets are machined with the nose down at a 7 degree angle. Negative inserts take a lot more rigid setup to make them cut than positive inserts.

    If the inserts you have are from a brake lathe chances are they are for machining cast iron and don't have a suitable chip breaker for steel.

    But there's only one way to find out and that is try them. If they are not suitable new insert's are not that expensive.

    See Ya
    Precision takes time.

    Comment


    • #3
      An insert for cast iron is usually mounted at a fair negative rake (tilted towards the workpiece.) This will require a great deal of effort on the handle to make a cut.

      For the ball-turning doodad (been thinking of making one myself) you're turning the tool by hand, so you'll want to minimize the pressure/effort needed to cut, and the tendency for the tool to "grab".

      I would use, like shown in the pics, a postive-rake insert, mounted "flat". Mill the pocket level, and either use tools with zero rake or with a built-in rake/chipbreaker.

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

      Comment


      • #4
        Thanks fellers! I think I'll just mill the toolholder flat and order some inserts like the ones shown on the website.

        When you say a very rigid setup is needed to use those Aamco inserts, my little 8x16 Sieg doesn't come to mind.
        Milton

        "Accuracy is the sum total of your compensating mistakes."

        "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

        Comment


        • #5
          I would recommend that you avoid negative or neutral angle inserts or brazed carbide tools (although the brazed tools are handy for clean up of castings and rusty stock - just not that good for fine workmanship) if at all possible as a beginner. You are far better off with positive geometry tools or just sticking with common M-42 or T-15 HSS tooling.

          Comment


          • #6
            Am doing the same - Bedair's ball turner. Baffeled by all the choices of inserts. Thanks for your suggestion Thrud. I have some 5/16" O-1 on hand. Can this be made to work?

            Comment


            • #7
              I have nearly finished my ball turning tool. All i need is a new 6mm tap and a few set screws and I will have it finished.

              Nearly had a tragedy when I snapped the blunt 6mm tap i had in the workpiece. Wouldn't come out so eventually i had to blow it out with the oxy.

              I had enough holes tapped to test it out and it works ok. It's a bit rough around the edges and is made entirely out of Black mild steel. The knob at the end of the handle is the first round piece I made on it..

              Oh yes almost forgot the other tool in the picture is a centre height indicator. When I use an unusual tool in the lathe and I need to get it on centre I put this tool on the cross slide and it tells me whether the tool is high or low. The base is cast iron and the rod is just some 3/8W threaded rod i had laying around. Very handy..


              [This message has been edited by Ringer (edited 12-28-2004).]

              [This message has been edited by Ringer (edited 12-28-2004).]
              Precision takes time.

              Comment


              • #8
                Looks like either a TCMT or a TPMT - that means a triangular with either a 7 deg. or 11 deg. angle (relief) molded tolerance & single sided with a chip breaker. The next thing to check is what size disk will fit around the insert, which is called the "inscribed circle". It has to touch all 3 sides of the top of the insert. If it's 1/4" it'll be probably a 21.51 if it's a 3/8" it'll probably a 32.51. Need a bigger radius just ask for a 2 nose radius & it'll be a 1/32" instead of a 1 which is a 1/64". Buy American J&L has a ton of them. Good luck.

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                • #9
                  Yes it's one of those inserts. I bought a packet of them from my suppplier. They are a lot more fragile than my WNMG's.

                  See Ya
                  Precision takes time.

                  Comment


                  • #10
                    The only thing I dont like is the head of the holddown screw is protruding out of the insert to far. That insert has a 60* countersink in it. Without the proper screw, your going to have chip clearance problems.

                    Comment


                    • #11
                      The hold down screw is just a caphead screw with a countersunk head i turned it down on the lathe.

                      The insert is not under a heavy load it works is all I can say. All the chips you see on the saddle were made by this tool...

                      See Ya
                      Precision takes time.

                      Comment

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