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  • Half Dead Centers

    I got a different #3 Morse taper half dead center today. This one looks real nice, fit's nice in the TS taper but when I retracted the quill to pop the taper out the quill stopped before the taper popped. Aw crap !!!!
    Well, after taking a closer look and pulling some measurements I found that the small end of the taper is about .050 larger in dia. than any of my other #3 tapers are.
    It needs to seat about an 1/8" further in to pop when the quill is retracted. I'm sure there are a few fixes out there, super glue a 1/8" thick disc to the end of it?? blob of weld ?? Grind the taper??

    JL................

  • #2
    Most often when that happens the OAL of the taper is short on the small end, (the big end seats at the normal position). My fix would be to build up the back end with weld or weld a 1/2" tang on there.

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    • #3
      Blob of weld or drill/tap/insert sound like less greif than re-grinding the taper.
      Location- Rugby, Warwickshire. UK

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      • #4
        Probably stating the obvious, but many times there is a threaded hole back there for a set screw/bolt to live, so that they can be adjusted for ejection...

        I will also point out that one of the beautiful things about half centers is that it is a simple affair to place an adjustable wrench on them ( using the flat ) and gently twisting, which results in their release. I do this fairly commonly on a certain gear hob that has a hydraulically driven tail that incorporates a spring loaded seating position. This results in loading the darn thing incredibly snugly, so the above is by far the easiest method to employ removing the centers.
        Last edited by Zahnrad Kopf; 02-12-2018, 08:25 PM.

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        • #5
          The recent thread: http://bbs.homeshopmachinist.net/threads/75615

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          • #6
            Here is a picture of the half dead next to one of my regular centers. The both look the same as far as length etc.



            Here is a picture showing how much of the end of my regular center protrudes from the end of an adapter bushing. The end of the taper protrudes about .146 from the end of the adapter.



            Here is a picture of the half dead center in the adapter. The end of the taper protrudes about .028 when seated.



            Best I can measure at the end of the taper..... the regular center measures .792 and the half measure about .801. Does that sound about right for all you math guys??
            .009 difference on the taper dia. equal about .118 difference in where it seats.

            JL.............

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            • #7
              Put a short plug of round brass inside the quill. Not to long so the longer taper will still seat. Small enough so it can be removes easily by taking the quill out and tipping it.
              Last edited by Juergenwt; 02-12-2018, 09:26 PM.

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              • #8
                Originally posted by Juergenwt View Post
                Put a short plug of round brass inside the quill. Not to long so the longer taper will still seat. Small enough so it can be removes easily by taking the quill out and tipping it.
                A lot of quills don't just come out that easily. An easier way would be to use a little slug of steel and then fetch it out with a magnet on the end of wand.


                But since we're talking about a difference of .146 -.028=.118" I'd make up a little slug of any old metal and just epoxy or use some other sort of glue. Or if you can drill and thread the end screw in a long set screw or a short round headed screw where the head is same or thicker than the difference. Depends on how hard the metal of the taper is.

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                • #9
                  Originally posted by Juergenwt View Post
                  Put a short plug of round brass inside the quill. Not to long so the longer taper will still seat. Small enough so it can be removes easily by taking the quill out and tipping it.
                  No I can't do that because then any taper with a tang such as drill chuck arbor won't seat.

                  JL....

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                  • #10
                    My solution was simple and does not require any permanent changes. Each of these delrin spacers has a rare earth magnet pressed into a recess.

                    Two different MT mounts, both too short. Two spacers that snick into place, giving exactly the right length.

                    At the end of the project, there is a profound difference between spare parts and extra parts.

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                    • #11
                      Originally posted by danlb View Post
                      My solution was simple and does not require any permanent changes. Each of these delrin spacers has a rare earth magnet pressed into a recess.

                      Two different MT mounts, both too short. Two spacers that snick into place, giving exactly the right length.

                      That's a good idea. A spacer held in place with a magnet makes it easy to use on the next taper that may have the same length issue. I don't use two tapers at the same time.

                      JL...............

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                      • #12
                        I have a smaller lathe that uses the same taper, so using the magnet allows me to remove the spacer when I want to use that live center in the smaller lathe. While it's in the smaller lathe the spacer sticks to the body of the tailstock.

                        Dan
                        At the end of the project, there is a profound difference between spare parts and extra parts.

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                        • #13
                          Originally posted by JoeLee View Post
                          Here is a picture of the half dead next to one of my regular centers. The both look the same as far as length etc.

                          Here is a picture showing how much of the end of my regular center protrudes from the end of an adapter bushing. The end of the taper protrudes about .146 from the end of the adapter.

                          Here is a picture of the half dead center in the adapter. The end of the taper protrudes about .028 when seated.

                          Best I can measure at the end of the taper..... the regular center measures .792 and the half measure about .801. Does that sound about right for all you math guys??
                          .009 difference on the taper dia. equal about .118 difference in where it seats.

                          JL.............
                          If you look, you will see that the half center is likely to be really shorter if measured from the "gauge line" of the taper, the point intended to be at the front of the quill, to the end. That's obvious from the seated positions.

                          So actually that is a "short taper". Put something on the back and get on with work. Magnet and delrin seems good, with fewer issues implementing it, but there are other solutions as well.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #14
                            Originally posted by danlb View Post
                            My solution was simple and does not require any permanent changes. Each of these delrin spacers has a rare earth magnet pressed into a recess.

                            Two different MT mounts, both too short. Two spacers that snick into place, giving exactly the right length.

                            Winner winner, chicken dinner!

                            Comment


                            • #15
                              Spacer with a magnet is a good idea, indeed. I just wonder what you used to attach it to Delrin, Dan. I'd, probably, used something more "glue-friendy" for the spacer.

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