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Square hole for tool bit

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  • Square hole for tool bit

    I would like to make a holder for a 3/8" lathe bit similar to a boreing
    head. This is for use in a radius turner to get the effect of a nearly
    complete ball on the end of a shaft the same diameter as the ball.
    I have the sliding dovetail ideas worked out but can't come up with
    a "simple" method to get the square hole. No I don't have an EDM
    available or any broaches. Have thought about drilling small holes in
    the corner of the location but then getting the bulk removed would
    still require a pretty small milling cutter and it needs to have a 1"
    cutting length. Not too encouraging.
    Any good ideas?
    Thanks.
    ...lew...

  • #2
    Square Hole Sleeves

    Lew, you might find these useful.

    http://www.jergensinc.com/infodir/ca...p?GroupNum=219

    Rgds
    Michael

    Australia

    Comment


    • #3
      Lew:
      you may want to check the archives this is one of those questions that has been kicked around a few dozen times. But in a nutshell.here are some of the more common ideas.
      1) drill round hole and file.
      2)drill round hole
      a) use commercial broach
      b) Make your own broach
      and use that.
      3) drill round hole set up in a shaper.make square.
      4) Drill round hole set up in lathe use lathe as a shaper.
      Tin
      Ad maiorem dei gloriam - Ad vitam paramus

      Comment


      • #4
        Drill four corner holes, one center hole. Remove as much material as you can with an end mill. Grind the end of a 3/8 toolbit to a hollow, then press it through the resulting pseudo-square hole. You'll end up with a perfectly square hole, and a very tight fit. If you need to have the bit slide out easily, you'll have to do a little filing. Otherwise the toolbit will be quite well secured in the holder by friction.

        On one job I did like this, I pressed the bit into a prepared hole in a short stub, then chucked the toolbit in the four jaw, centered nicely, and turned the stub true. Then I prepared the tool holder to accept the stub. I figured this way I'd have control over the geometry, and it worked out fine. I also found it easier to press the bit through the stub when the stub wasn't much larger than the toolbit.

        I've been saying press, but what I actually did was hammer it through.

        I've also considered, but never tried, milling a dadoe out of two pieces of metal such that when the two pieces are put together a square hole of the right size is created. I would then braze or silver solder the pieces together. That's another way to end up with a square hole to hold a tool bit. You would also get to define an angle for that hole if you wanted to.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          For some of my "emergency" boring bars I have used a round reamed hole (1/8",3/16", 1/4" or 5/16") to accept broken center drills that have been converted to tool bits.

          Hope this helps,
          Frank

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          • #6
            I would use a 3/8" endmill to put a slot into the end of the tool bar maybe 3/4" deep and then silver solder a pc of 3/8" keystock flush with the outer edge. Wala, a 3/8" square hole. Course, if you don't have a way to mill or solder...

            Edit: Oh I see Darryl already went over this--It does work well if you have the means. Have fun! SG
            Last edited by sidegrinder; 05-15-2007, 12:25 AM.

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            • #7
              SG, that's another way to do it I hadn't thought of, thanks for that idea.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

              Comment


              • #8
                Use cheap import sockets.

                They weld and machine well.

                Comment


                • #9
                  I've done most of the methods listed here, including making a square broach. imo the easiest is fabrication as Darryl mentions, mill a slot, braze or silver solder a cap on it, and turn or mill locating off the square hole. works well.
                  .

                  Comment


                  • #10
                    Square hole for tool bit

                    Deleted/edited-out
                    Last edited by oldtiffie; 08-19-2007, 06:24 AM.

                    Comment


                    • #11
                      Do it the easy way like Miker linked to. Use a pre-made square hole sleeve. They can be purchased plain or with an adjustment screw to adjust the bit extension.

                      One of the main usages of square hole sleeves is to do exactly what you have in mind. Just drill a round hole and insert the sleeve.

                      For a 3/8" size I imagine you'd have to pay the princely sum of close to $10.

                      Jergens and Sturdy Broach Company are the two main suppliers in the states. Jergens sleeves are made of 12L14, not weldable, but can be brazed. Sturdy's sleeves are weldable or can be brazed.

                      All tooling house sell these.


                      BTW, it never ceases to amaze me the difficult solutions responders on this board come up with to do the simplest things. I can't imagine a simpler solution than a square sleeve yet look at some of the ideas presented here.

                      Comment


                      • #12
                        Square hole for tool bit

                        Originally posted by PolskiFran
                        For some of my "emergency" boring bars I have used a round reamed hole (1/8",3/16", 1/4" or 5/16") to accept broken center drills that have been converted to tool bits.

                        Hope this helps,
                        Frank
                        This is the quickest and easiest solution IMO. Center drills and end mill shanks make excellent cutting tools and there are usually plenty of them around. Also, tap shanks work well too. This beats the heck out of filing for half a day to make a square hole in each end of a bar, as I once did.
                        Jim (KB4IVH)

                        Only fools abuse their tools.

                        Comment


                        • #13
                          How deep? What kind of material? How many?

                          Depending on depth, quantity and material to be cut, the off the shelf square rotary broach may be able to be pressed in. It will cost around $70. On a CNC this can sometimes be done in a pecking mode. Any good guys in your part of the woods who would loan you a rotary broaching toolholder ? You can make square holes all day long with these things.

                          Comment


                          • #14
                            Originally posted by peter08
                            Depending on depth, quantity and material to be cut, the off the shelf square rotary broach may be able to be pressed in. It will cost around $70.
                            A rotary broach isn't pressed into the work, it's run sort of like a drill but with the broach rotating with the work - that's why it's called "rotary broaching". It's also called "wobble broaching" as the broach wobbles with the rotation of the work, and it's the wobble that does the cutting. A good description of the process here: http://www.sommatool.com/manuscripts/broaching.asp

                            Lew - if you're still looking for a solution I think I have one of the square Jergens inserts on the workbench. Give me a call and I'll double check the size, if it works it's yours - just replace it when convenient.

                            Comment


                            • #15
                              Thanks for all the great ideas. I got it done by a combination of the
                              ideas. Drilled the four corners, drilled the center a 1/64 under size,
                              set the digital readout to zero and proceded to mill with a 3/16
                              cutter (round and round the square) and finally pushed a 3/8 bit
                              through to clean up the tinny bits left. Had to do it from both sides,
                              the block is about .900 (cleaned up 1" stock) and the 3/16 cutter
                              only had 1/2 inch reach.
                              In the future the ready made square holes in a round peice looks
                              like a winner. but the silver soldering a "filler" into a slot also looks
                              good and would be cheaper. The clamping setscrews probably should
                              not go through the added block but at right angles to it.
                              Oh well next time. :-)
                              Thanks again.
                              ...lew...

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