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R8 to JT6 Arbor to 1/8"X 5/5" Keyless Chuck

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  • R8 to JT6 Arbor to 1/8"X 5/5" Keyless Chuck

    I have an R-8 to JT6 arbor that I bought from Enco about 10 years ago with a 1/8" to 5/8" Keyless chuck. It's been used hundreds and hundreds of times to drill holes using the former H.F. Mill drill and more recently my Webb (BP Clione). A couple of times recently when drilling a 1" hole at low rpms in a 1" plate, the chuck has come loose.

    I examined the stub on the arbor and it's got some scratches on it. Close inspection of the inside of the chuck with a jeweler's loupe and a strong light indicates that the chuck is unscathed. Apparently, it's made of harder material that the arbor. That's the only luck I've encountered recently.

    To be on the safe side, I ordered a new R8-JT6 arbor on eBay this afternoon. The other one goes in the heap.

    By the way, I looked for a chart of Jacobs Taper dimensions and discovered that a JT6 has a major diameter of 0.6760 and a minor diameter of 0.62410. As near as I can measure the old arbor is extremely close to those numbers. I wanted to be certain that the one I have is really a JT6 and those dimensions are the only ones even close so I'm certain that's what it is.

    My questiion is this: What is the preferred method for attaching my new arbor to the chuck so that it might stay on for another ten years or so?

    1. Dry with pressure with 20 ton press?

    2. Pressure with 20 ton press and red Loctite?

    3. Dry with BFH on anvil?

    4. Other?

    Suggestions will be happily reviewed and advice humbly put to use with profuse expressions of gratitude.

  • #2
    The method that has worked for me is as follows:

    All surfaces made really clean - I use Lacquer thinner.

    Put arbor into chuck and wack it together on a piece of wood using a deadblow hammer (just a medium wack!). (first retract the jaws into the body).

    Good luck.

    Geoff

    Comment


    • #3
      Originally posted by ammcoman2
      The method that has worked for me is as follows:

      All surfaces made really clean - I use Lacquer thinner.

      Put arbor into chuck and wack it together on a piece of wood using a deadblow hammer (just a medium wack!). (first retract the jaws into the body).

      Good luck.

      Geoff

      I'll try that first when the new arbor arrives. Thanks.

      Comment


      • #4
        Drill Chuck taper

        You are probably pulling the chuck off the taper when you break through the 1" plate. Especially at low RPM when the center is gone out of the material, the outer lips of the drill will dig in and take too much of a bite. That will jerk the chuck off any taper. It's like trying to mill with a Morse taper end mill holder with no drawbar. The end mill will pull it out every time. When you get close to the bottom on those big holes, use higher RPM and use the spindle downfeed stop to gradually lower the spindle in a controlled manner so it can't dig in all at once. You are probably getting the scratches when the chuck pulls off. Seat the taper with the new arbor as described above.

        Comment


        • #5
          Originally posted by Toolguy
          You are probably pulling the chuck off the taper when you break through the 1" plate. Especially at low RPM when the center is gone out of the material, the outer lips of the drill will dig in and take too much of a bite. That will jerk the chuck off any taper. It's like trying to mill with a Morse taper end mill holder with no drawbar. The end mill will pull it out every time. When you get close to the bottom on those big holes, use higher RPM and use the spindle downfeed stop to gradually lower the spindle in a controlled manner so it can't dig in all at once. You are probably getting the scratches when the chuck pulls off. Seat the taper with the new arbor as described above.

          You are probably correct in that the issue is drilling larger holes. As far as the downfeed, that's limited to 3/8" on BP's and clones. I had to tear into my Webb when I first got it and replace the downfeed bevel gears. I'm not going to take a chance on anything large.

          I use the downfeed for boring and otherwise light duty. They are a rather weak design.

          But I agree that a 1" drill is probably a tough test for a JT6, which although one of the larger JT's, is still rather small.

          Thanks.

          Comment


          • #6
            The correct way to put a chuck on an arbor is to heat the chuck in an oven to about 200 degrees F and drop it on the spindle. It will not come off. Some say to put the arbor in the freezer as well but thats a good way to get moisture between the surfaces of the taper.

            A bridgeport is rated 3/4" manual feed, 3/8" power feed.

            Comment


            • #7
              Originally posted by macona
              The correct way to put a chuck on an arbor is to heat the chuck in an oven to about 200 degrees F and drop it on the spindle. It will not come off. Some say to put the arbor in the freezer as well but thats a good way to get moisture between the surfaces of the taper.

              A bridgeport is rated 3/4" manual feed, 3/8" power feed.
              My Webb manual only mentions 3/8" downfeed limit. Nothing in there about limiting manual.

              So you say that you can't drill a 1" hole with it. I used to do 1" holes on my mill Drill. I'll have to check that out. After this problem, I'll probably quit drilling big holes with it.

              Yeah heating the chuck is a good idea. I have a dedicated toaster oven for just such an eventuality.

              Thanks.

              Comment


              • #8
                Why wouldn't you just bring the taper back to new condition and reinsert it? Seems to be a bit of a waste to just chuck it...after all, you consider yourself a home shop machinist and isn't this sort of repair right up a HSM's alley?
                Location: Saskatoon, Saskatchewan, Canada

                Comment


                • #9
                  The downfeed stop I was referring to is the quill stop - a threaded rod on the front of the head parallel to the quill. You can bring the quill to a stop and then screw the stop nut down the threaded rod by hand incrementally. This way the quill can only go as far as the nut. Drill - turn the nut 1/2 turn or so, drill - turn the nut, etc.

                  Comment


                  • #10
                    Originally posted by Arcane
                    Why wouldn't you just bring the taper back to new condition and reinsert it? Seems to be a bit of a waste to just chuck it...after all, you consider yourself a home shop machinist and isn't this sort of repair right up a HSM's alley?
                    If I were to do that, it would seat deeper and there would be no clearance behind the chuck and the arbor. It's already less than 1mm...I guess it could be done. I'll just save it for the day when I find another chuck.

                    I thought of perhaps doing that. I would have to figure some way to chuck it. The bearing surface is at the end of the R8 portion and there is no center in the JT portion. Even assuming the use of soft jaws with a good tight fit in the chuck, it would be unwieldly unless I could get a live center on it. It would really need to be supported on each end.

                    Maybe someone has a method for doing this.

                    Interesting idea, though.
                    Last edited by gnm109; 09-06-2010, 12:12 AM.

                    Comment


                    • #11
                      Originally posted by Toolguy
                      The downfeed stop I was referring to is the quill stop - a threaded rod on the front of the head parallel to the quill. You can bring the quill to a stop and then screw the stop nut down the threaded rod by hand incrementally. This way the quill can only go as far as the nut. Drill - turn the nut 1/2 turn or so, drill - turn the nut, etc.

                      I see. Yes. I could do that. I also have a clip on moveable quill stop.

                      Comment


                      • #12
                        Originally posted by gnm109
                        My Webb manual only mentions 3/8" downfeed limit. Nothing in there about limiting manual.

                        So you say that you can't drill a 1" hole with it. I used to do 1" holes on my mill Drill. I'll have to check that out. After this problem, I'll probably quit drilling big holes with it.

                        Yeah heating the chuck is a good idea. I have a dedicated toaster oven for just such an eventuality.

                        Thanks.
                        I think thats just what they determined as to what the splines could take under normal use without significant wear during the warranty period. My best guess. After all its supposed to be a mill, not a drill press!

                        Comment


                        • #13
                          If you're drilling a 1" hole, you're probably using a Silver and Deming bit (1/2" reduced shank), in which case I always just hold those in a 1/2" collet. That way it's more rigid, more concentric, and it gives you more daylight between the tool and the piece. I find I can do a lot of projects without removing the 1/2" collet since I have an edge finder with a 1/2" shank (Starrett 827B), 1/2" endmills, 1/2" spotting drills, and the Silver and Deming set. That reminds me, I really should get a small drill chuck and put a 1/2" straight shank on it for the smaller bits.
                          Stuart de Haro

                          Comment


                          • #14
                            Originally posted by hornluv
                            If you're drilling a 1" hole, you're probably using a Silver and Deming bit (1/2" reduced shank), in which case I always just hold those in a 1/2" collet. That way it's more rigid, more concentric, and it gives you more daylight between the tool and the piece. I find I can do a lot of projects without removing the 1/2" collet since I have an edge finder with a 1/2" shank (Starrett 827B), 1/2" endmills, 1/2" spotting drills, and the Silver and Deming set. That reminds me, I really should get a small drill chuck and put a 1/2" straight shank on it for the smaller bits.

                            Yes, you're correct about the 1/2" collet. I general;ly do that. In this instance, I did not and it came off. We live and learn.

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