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  • How to put a round pin in a square hole

    I need to put a boring bar on my lathe, I know that the commonly available QCTP's will do this, (look at my QCTP thread) However why spend the coin if I dont have to as pointed out by a few. I thought about making a block of steel with a 1/2" hole in it. and a couple of set screws to hold the bar, then chuck it in my 4 way, use feeler gauges to set the height and start cutting. Is this the best way? Anybody have a photo of what it is supposed to look like? Any tips for a guy who is not a machinist and is kinda clueless as to what I am doing? Keith

  • #2
    I did something similar on my first lathe and it worked fine. I put a Jacobs chuck in the main 3-jaw and center drilled the block (previously mounted on the compound) then drilled the finished hole. I figured this was the easiest way to get the center lines to match. I bored a lot of holes with this setup until I was able to buy a QCTP.

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    • #3
      Hi.
      something like this perhaps.


      cheers
      Roy

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      • #4
        I originally made this double barreled one for my fourway before I got my quick change. It works in both tool holders.For 1/2 and 3/8 boring bars. ( no I dont use both bars at once!!! LOL )



        I made a couple of singles later on for the QCTP



        Ernie (VE7ERN)

        May the wind be always at your back

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        • #5
          Thanks for the pics, and the tip about drilling it on center. I think I have some 1.5" x 1.5" stock at the house, if not the local steel supply is flush with the stuff. Thanks guys. Keith

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          • #6
            There is also this option sized to fit your boring bars and 4-way.

            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia

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            • #7
              That is a novel approach, I never thought to drill it on size and make a relief cut and use the set screws to hold it, I was worried about the margins but I'm sure that if I have some 1"x1" CRS I will have enough room for what I have in mind. Also I'm only cutting 6061 when I'm done and I can take all day to make the cut I'm in no rush. Not like I am cutting 304SS with a time clock ticking. Thanks again. Keith

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              • #8
                I drilled out a blank tool holder for the boring bar.

                Andy

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                • #9
                  Those are some nice looking boring bar holders. My compliments to all.

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                  • #10
                    Location: North Central Texas

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                    • #11
                      Well I did it I came up with a way to hold the tool bit. More on that in a bit. Anyway here are is a pic of the results.

                      Now here is how I did it. Please dont kick me out!
                      I was planning on taking a 2" long x 2.5" CRS mill it to fit my 4 way, bore it to hold a boring bar and do it that way.

                      Then the red-neck side of me comes out on the walk to the shop. I did tell you I'm nothing more than an educated hill-billy right? Anyway I start thinking about all the work ahead just to make a tool to make a part, not a cool part just a little adapter, and its the only part keeping my Jeep off the trail. So I start thinking, why cant I just bolt the thing down in the 4 way?? I mean Im just cutting AL and they are shallow cuts. Im at the shop now and I am thinking about this plan.

                      First problem, height, I drop the round pin in the square hole and I'm low real low. So I put an 1.8" shim under the bar and it brought me REAL close to center. Next problem rigidty, So I chuck up a length on 3" thick wall AL tube, same material as my work piece and same dim. So I put it in the tube, run the cross feed out till I make contact, add a few thou and engage the carraige. IT WORKS!!!!! Next up a deeper cut 0.010", works! 0.020" works!!
                      No chatter, clean even cut.

                      Now I know that this was not bright, and could have even been danger inducing. However The lock pins set in front of the centerline of the boreing bar locking it into the four war, and it was a brand new bar so it was very sharp and I was, for the first time, using ALL the safty guards, no cuts were made with the shield up, I never stood infront of the work while it was cutting and I always wear eye protection.

                      Yep its a dumb way to do it, yet it yielded good result with no drama. Is it the way I'm going to do all my boreing operations? Nope! All it did was allow me to move forward with this project until I can afford a proper tool holder, I have decided that a Phase II QCTP is in my near future, just need to add a few more bucks to the tool fund, as I made a decent withdrawl to cover the last batch of HSS tool bits I ordered from ENCO. Keith

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                      • #12
                        I made one like Ernies below only I used aluminum and it works fine. Probably wouldn't hold up for commercial duty but for home use it's fine with a 3/4" bar in it.

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                        • #13
                          If you are saying that you just clamped a boring bar in a 4 way tool post holder with a shim under it, I don't think you are the first "red-neck" to do that.
                          I bet this forum is full of such.
                          Vitَria, Brazil

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                          • #14
                            [quote=dockrat]I originally made this double barreled one for my fourway before I got my quick change. It works in both tool holders.For 1/2 and 3/8 boring bars. ( no I dont use both bars at once!!! LOL )


                            quote]

                            I imagine that amount of overhang must be prone to chatter except on very light cuts .



                            If you are saying that you just clamped a boring bar in a 4 way tool post holder with a shim under it, I don't think you are the first "red-neck" to do that.
                            I bet this forum is full of such.
                            davidwdyerIf you are saying that you just clamped a boring bar in a 4 way tool post holder with a shim under it, I don't think you are the first "red-neck" to do that.
                            I bet this forum is full of such.

                            Isn't that the correct way then

                            john
                            John

                            I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

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                            • #15
                              ever tried to bore two holes, at the same time, on your lathe with that.

                              Give it a try and get back to us.
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                              Southwestern Ontario. Canada

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