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A between centres boring bar for internal tapers

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  • A between centres boring bar for internal tapers

    Huh? how the heck does that work? Well, paging through a neat old book, Modern machine shop practice from 1887, I saw a set up for boring a large internal taper with a between centres boring bar. Pic is below reveals how this is done.

    Sometimes you hear the notion 'how did they build anything back then"..... as if because someone else invented the microprocessor we're all smarter than the boys 100 years ago lol. Maybe it's the opposite ....given they had no electronics or cnc..... I don't think I'd have come up with that setup in a month of Sundays...hope you get a kick out of it.

    Last edited by Mcgyver; 10-21-2012, 11:23 AM.
    .

  • #2
    It appears to be pulled along toward the tailstock (or pushed toward the headstock, if I'm seeing the cut in the bore) by a leadscrew on the bottom driven by a gear on the end and a matching gear on the tailstock dead center. Looks like a lot of fun to setup.

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    • #3
      Cutting head slides on shaft, held in alignment by sliding key on shaft. Cutting head is advanced by the interaction of gear A on live center and B on leadscrew.

      Yet another reason to seek out, collect, read and aborb the knowledge contained in old machining books.

      Mcgyver, you're right, how did people survive with out CNC guided tools? Actually having to use their brains to solve a complex problem using ingenuity and off the shelf parts. Seems almost impossible.

      Modern Machine Shop Practice, authored by whom? Colvin and Stanley or someone else?
      Found it. Google books, MMSP by Joshua Rose.
      Last edited by Rosco-P; 10-21-2012, 11:44 AM.

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      • #4
        I get how it how it works, the "Huh?" is hypothetical.... as in how the heck would you do that without having seen the pic

        the book is online as high res pdf's, really interesting stuff.

        If you download it, the other things that strikes me is what a monunmnetal task it would have been creating that 2 vol set. There's 1000's of illustrations (woodcut?), all beautifully done.....and all the layout was of course all manual. cloes to 1000 pages. Amazing to think of the work that went into that.
        Last edited by Mcgyver; 10-21-2012, 12:12 PM.
        .

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        • #5
          Mac,
          Very cool and that's certainly a new one on me. No way in hell I would have figured out how to do that job. Somebody was a genius. I look at some of the pictures of those massive ship board and stationary steam pumping engines today and still wonder how they got them even built given the casting, machine tool average accuracy, and even the cutting tool technology they had at the time. Some of the convoluted designs used on some of the lesser known types to get around some patents made the parts really complicated to build. If you look at the amount of inventions and accuracies involved along with the mass production using strictly mechanical methods during the pre CNC period, it's pretty mind blowing what they got accomplished. I think those old books are just as useful and interesting today as when they were first printed. Those old school guys got it done on shear sweat and brain power.

          Pete

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          • #6
            Originally posted by uncle pete View Post
            I think those old books are just as useful and interesting today as when they were first printed. Those old school guys got it done on shear sweat and brain power.

            Pete
            Exactly Pete, however it's like preaching to the choir. They (we) already get the message. There are some who will spend nearly a thousand for a machine, tooling and marginally useful far-East accessories, but won't buy a reprint of South Bend's HTRAL.

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            • #7
              I wish I had taken a photo of the facing operation for the forward gun turret on the DD's I worked on but I don't think they had cameras then... can't remember. In any case it had to be done in situ so the machinist's and engineers had to cobble up a large facing machine that would fit through hatches. It took 8 hours to make one pass and if your tool chipped you had to start over. Boring the shaft bearings was another sight to see.

              John
              My Web Site

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              • #8
                We used to bore tapered body fit bolt holes in propeller flanges in Navy ships with a gadget much like that but much beefier. The apparatus in the illustration looks spaghetti limber.

                It must be a million years old by now but when I last saw it in 1992 the tool shop had freshly rebuilt it. 1/4" per foot taper and the bolts were fitted to have 1/8 to 3/16 draw.

                The bolts varied from 2" to 3 1/2" dia and were 7 to 11" in grip made of Mil-S-890 class II (4340 HT to 180 KPSI.) Install them with plenty of sheep tallow and draw them up. Torque with a slugging wrench to where it sounds right about2800 ft lb. 21 body fitted bolts 3 1/4" dia on a 39" bolt circle holding togeter 44" dia flanges each 7" thick made a pretty stout connection.

                Naturally this was portable stuff designed to mount on the shaft with monster chain clamps and be manually positioned from hole to hole. The drive was a #4 angle air motor. The tool was fed out with a setscrew and clamped by another. Slick piece of portable tooling. Two months of work in this scale will muscle up a young man a full shirt size. Thanks for stimulating my memory..
                Last edited by Forrest Addy; 10-21-2012, 04:03 PM.

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                • #9
                  I wonder if the guy who made the drawing had ever seen this process in action, it would also be interesting to hear from anyone who ever actually tries to follow this idea.

                  As it is drawn the tool will cut a helix of a pitch coarser than the pitch of the feed screw.

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                  • #10
                    I am actually surprised the tool feed doesn't include a star wheel arrangement to reduce the feed to something finer then the feed screw pitch. Other than that, it is pure mechanical genius.

                    I hired some mobile machining done one time that had a star wheel feed and a spring loaded pin. If the tool started to bog down the guy pulled the pin and made a couple of "spring passes"
                    Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                    • #11
                      Here is one in use.

                      Not exactly identical, but close.

                      Taken from the Doxford archives. http://www.shipsnostalgia.com/guides...turing_Process



                      Dave

                      Last edited by becksmachine; 10-21-2012, 05:49 PM. Reason: Dead link

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                      • #12
                        Cam, look at the right end of the appartus in the illustration at the parts labeled A and B adjacent to the center. I believe the slender part beneath and parallel to the thicker part is the lead screw and A indicates the feature on which mounts the striker and B the star wheel on the end of the feed screw.

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                        • #13
                          Very glad this was posted, can't help but think, "What is old, is new again." at least to me.

                          Would have taken years to think of making a between centers boring bar that tapers to each end, yet, really, I supposed it is a simple engineering principle. Other "most useful", for me, is the idea of cutters pulling not pushing.

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                          • #14
                            Nothing could be truer about what is old is new again one of the new cars has a hill holder push in the clutch and it holds the brakes on, just like my 1950 Studebaker

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                            • #15
                              Here's even more to look at:

                              http://www.hnsa.org/doc/index.htm#shop

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