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  • What drill bit?

    I am in the process of trying to resurect a old Cushman 3 jaw chuck.
    It is now clean, tolerances checked, and ready to try and make accurate.
    Somebody in the past attempted to grind out the inside jaws and goofed.
    My idea is to drill a hole in each chuck jaw,ream,insert dowel pin, clamp a short tube and regrind the inside jaws with a toolpost grinder.
    I tried to drill a hole in the jaw and found out it is hardened,OK I figured it was casehardened and after I drilled a pilot hole thru the case it would work.
    The only drill I had in the shop that worked at all(sort of) was a carbide tip masonry drill and I found out it is NOT just a surface hardness but all the way thru.
    Any ideas on what drill bit to get?
    Thanks,
    Rob



    [This message has been edited by roberlt (edited 01-08-2003).]

  • #2
    Might hit through it with a cobalt drill bit with a 135 degree point angle. I have done this before. A carbide drill bit run somewht slow will also work, 135 degree point. Spot drill or center drill for both, probably a carbide spotting drill. Most likely these master jaws are 4140 hardened.
    CCBW, MAH

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    • #3
      Use the masonery drill if you don't have any thing else. The only problem is an oversize hole, but thats OK if it's 1/2" deep, it will work. Reaming is a waste of time and tooling. The holes don't even have to be in the same spots on the jaw, as all you want is a load point for the ring.
      A dowel pin is nice, but a piece of drill rod works, and if too loose, just give it a smack first and flaten a little to tighten it up before putting it in.
      The best way to drill with a masonary drill, is to remove the 3 jaws and clamp them together, and place them in a cake pan, and have some water in a pitcher. As you drill with the bit,AT MAXIMUM SPEED !, pour water on the drill> read Flood! and push hard at the same time. the masonary bit will walk thru it ! The reason for the water , is to keep it totally cool. A masonary bit has a silver soldered carbide point on it. If it gets too hot,it will come apart. This doesn't happen when drilling masonary, because your hand rill can't push enough on it, but a drill press will !

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      • #4
        Tried to do that also, and found masonry drills just ain't made for metalworking.

        Use a die drill, or a regular carbide will get a better hole. And they are made in smaller sizes for smaller jaws

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        • #5
          Rob

          Any Hi-Roc (M.A. Ford) drill, or square die drill (all solid carbide) will cut it like butter. www.icctool.com , travers, J & L, etc.

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          • #6
            Rob,

            Instead of drilling and inserting pins, take a disk of (say) 10mm plate. Bore 3 offset holes, and then a fourth hole in the centre. The central hole should intersect the 3 peripheral holes, each of which should slip over the front step of the chuck jaws.

            You'll have something that looks like a threading die with 3 cutting edges.

            Slip it over the front of the jaws and tighten the jaws inwards. Then use the toolpost grinder.

            HTH,

            Ian
            All of the gear, no idea...

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            • #7
              MSC lists "2 flute solid carbide 140 degree straight flute drills" in the size I need.
              Think this is OK for what I want to do?
              Thanks,
              Rob

              Comment


              • #8
                Ian has got the right idea. It's the best way to go if you have one piece jaws. If you have two piece jaws, another way is to make a ring with three equally spaced pins sticking out of one face. The pins fit into the holes that hold the jaws on.
                Big Dipper

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                • #9
                  Oso

                  I've seen in HSM or Projects in Metal a helpful hint where someone drilled a hole through a file with a carbide masonry bit. They did mention using a ton of water. Drilled a nice little hole too.

                  Peace

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                  • #10
                    I am afraid I do not understand Ian's suggestion.
                    The jaws only have one surface to grip the outside of a workpiece so if I close the jaws on something then I can't grind them.
                    If I have not understood the answer properly please let me know.
                    Thanks,
                    Rob

                    Comment


                    • #11
                      Rob
                      Check to see if they have the square die drills, they are much stronger and less likely to break. The die drills can go through full hardened steel with light pressure.

                      The one you mention can work. Make sure the work is firmly clamped in the vise and that the tip does not wander (needs a flat surface to start) or it can shatter. If it is carbide tipped HSS it will be more forgiving of errors. You could always regrind a good masonary bit to give it some bite.

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                      • #12
                        Robert,

                        I can imagine why you're confused, it's probably easier to make this thing than it is to describe it...

                        The idea is that the surface of the jaws that normally grip the work poke through the three gaps produced by boring one central hole in the ring of three (smaller) holes.

                        There are six contact points, the jaws contact the ring on their flanks.

                        Here's another way - same effect, may be easier to make:

                        Take a disk of steel, bore a central clearance hole. In a circle outside this hole, bore three small (eg. 1/2") holes, press 3 hardened parallel pins into the holes. You now have a steel ring with 3 pins sticking out.

                        Close the chuck jaws onto the pins, such that the pins are trapped between the faces of the jaws that normally meet when the chuck is fully closed. The chuck can be tightened in the closed direction, yet the normal gripping faces of the jaws are free to be attacked with a toolpost grinder. Same principle.

                        HTH,

                        Ian
                        All of the gear, no idea...

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                        • #13
                          The disk works Ok if made perfectly, but inaccuracy of the holes seems to lead to problems using it. I had bad results with it, but perfect with the pin method.

                          Others have reported same. There just doesn't seem to be a way to do the pin method wrong.

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                          • #14
                            Ian
                            Thanks for the update. Since this chuck is not anywhere near new I think I will use the pin method. To quote a frends young son it will probably work "much gooder"
                            Thanks,
                            Rob

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                            • #15
                              IT WORKED!
                              Got the drills I mentioned from MSC, and drilled the holes.
                              THANK YOU all for your help

                              Rob

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