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  • Boring a deep hole??

    Hi Folks, Here's a little progress on my junk bin engine. Need some advice on deep hole drilling. have tried twice now to build a stepped sleeve for the crankshaft which accomodates the flywheel and pulley.

    Using the lathe, first time I tried sneaking up on the ID with 3 bits but the bottom of the bore was out .007" side to side over the 7/8" Dia. sleeve, I could see this by eye and knew it was wrong before I measured it with my caliper.

    The second time I tried 1 bit, measures ok with the caliper and it looks good to the eye when I spin it on the shaft. But once I put the flywheel on I can see a slight wobble. Measured with a dial indicator, has run out of almost .005" on the outer edge of the wheel.

    I am trying to drill a 15/32 hole 2.200" deep. My boring bar is to big to fit so I can't use it. (wish I had this problem elsewhere).

    What am I doing wrong?

    Cheers, Bob




  • #2
    What you are doing wrong is useing a drill bit to do precision work, it dont work. Using a drill bit , drill the hole somewhat undersize, then finish by boring the last few thou with a boring bar. Tiny boring bars are cheap and are prone to flex a lot so go only very few thousandts at a time making multiple passes at the same setting. It can be done! JIM
    jim

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    • #3
      If your drilled hole is running true, use a chucking reamer. They're relatively cheap, quick & easy.

      David
      Wet & rusty Montezuma, IA
      David Kaiser
      “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
      ― Robert A. Heinlein

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      • #4
        If I read you right, it sounds like you're trying to get the bore concentric with the outside diameter. If that's the case, use a piece of stock slightly oversize, bore your hole, and then fit the stock onto a mandrel and turn the outside diameter.

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        • #5
          Youre just going to have to buy a boring bar that fits your application.

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          • #6
            5 diameters deep is not bad, 20 diameters deep + gets tricky.

            You can get a drill to run true by boring a short ways in like a pilot hole to start the drill strait, drill and ream to size from there, works like a champ.

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            • #7
              Line boring

              "Trepan" or "Line bore" it.

              There have been quite a few posts on these topics in the fairly recent past. Perhaps some will be good enought to post links on these topics that are relevent to the OP.

              Some other references may be found here:

              http://books.google.com.au/books?id=...sult#PPT664,M1

              http://www.google.com.au/search?hl=e...e+Search&meta=

              http://www.youtube.com/watch?v=_J9ak3wKtPQ

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              • #8
                A different approach is to rough machine the sleeve, bore/drill the hole and finish turn the OD with the sleeve mounted on a mandrel.

                A simple stub mandrel can be turned up to accomodate the sleeve. If turned on the lathe and not removed from the chuck, it will run true.
                Last edited by JCHannum; 06-14-2008, 08:31 AM.
                Jim H.

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                • #9
                  Thank you for all the advice. Think I really did it to myself. When I machined the sleeve to fit the flywheel I wanted a good prees fit. So I thought I would be clever, made the sleeve .001 larger than the bore on the wheel. Took my goodies to the house, plopped the wheel in the oven at 450 for 1/2 hour and stuck the sleeve in the freezer. Holy cow, it worked!! The sucker just dropped right in place.

                  Well, I wish I had known there was going to be a wobble for one and two, I wish I had asked how to drill the hole before I needed to, but then again anyone can drill a hole...right?...wrong. Now I can't get the darn thing apart to try all these great ideas. Maybe I can just put it together and tell everone I made it that way on purpose, and that costs extra.

                  Cheers, Bob

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                  • #10
                    You could always figure out how to bore out the sleeve and put a new one in but it doesn't sound fun.

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                    • #11
                      True

                      Originally posted by JCHannum
                      A different approach is to rough machine the sleeve, bore/drill the hole and finish turn the OD with the sleeve mounted on a mandrel.

                      A simple stub mandrel can be turned up to accomodate the sleeve. If turned on the lathe and not removed from the chuck, it will run true.

                      Thanks JC (not THAT "JC" I presume).

                      That is far and away the best approach, but it needs to be incorporated as part of the "Job Plan" before the job is ever put on the machine.

                      But as the part was all but finished before the "true-ing" of the hole/bore was even started, another approach is needed.

                      All-in-all, it seems to have turned out (unintended pun!!) OK and lessons have been learned.

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                      • #12
                        Here is what I would do to get a good true 15/32 dia. over 2 inches deep.
                        Centerdrill, drill 1/64 undersize, bore with a short boring bar about 3/8 deep to
                        slightly under 15/32 and use a 15/32 reamer to follow the bored hole. Go easy on the reaming to give the reamer time to cut. Use a good lubricant and bring the reamer out once in a while to clean out the chips.

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                        • #13
                          Trepan

                          Agreed juergenwt.

                          That is effectively a self-centered and self-centering "piloted" "trepan".

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