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  • Turning between centers??

    I was watching a video from tubal cain on you tube. He was making a pulley, and turning it between centers on an arbor. He drilled and reamed the hole and pressed it on the arbor. All I understand. My question is, wouldn't pressing that on the arbor "stretch" the bore a little? Or am I over thinking things. I'm sure I will learn more about it next month. Couriousty has me

    Thanks,
    Chris

  • #2
    It may "stretch" a little but unless it's way over-done, it won't "yield". i.e., it goes back to where it was. Every time you snap in a morse taper center into a tailstock, same thing happens.

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    • #3
      I realize that I may be picking nits here but parts are generally turned on a mandrel, not an arbor. Mandrels have a slight taper (.003 or so per foot) so that they can be pressed tightly into the part. Arbors on the other hand are straight (no taper) and are more commonly used for holding cutters, think the arbor on a horizontal mill.

      However mandrels are pressed into a part using an arbor press. Go figure
      Errol Groff

      New England Model Engineering Society
      http://neme-s.org/

      YouTube channel: http://www.youtube.com/user/GroffErrol?feature=mhee

      Comment


      • #4
        Errol is correct. As an apprentice this was emphasized with such importance that it was a pass/fail question on a test. 49 correct answers and that one wrong? You flunk.
        Arbors hold tools. Mandrels hold work.
        Last edited by tdmidget; 07-25-2012, 04:39 PM.

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        • #5
          So you guys are saying that if I turn a straight section to hold a part, it is wrong as it is a tool holder? *confused*

          You make what you need to hold work or a cutting tool, doesn't matter what's it called, was it an arbor, a mandrel or a jig.
          Amount of experience is in direct proportion to the value of broken equipment.

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          • #6
            Ok a mandrel lol. I didn't know that, now I do. And thanks for the explanation.

            Chris

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            • #7
              If it holds the workpiece, it is a mandrel. Arbors hold tools, such as the arbor on a bench grinder or the piece that a drill chuck is mounted on.

              We had several such questions. Another was the difference between a bolt and a screw.

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              • #8
                An arbor has a straight shank and a shoulder for the work to rest against with no taper and a nut to hold the work while it is machined or if an arbor for a cutter to hold the cutter without slipping.

                A mandrel has a slight taper so it wedges into the bore of the work so it can be turned between centers.

                That's about as simple an explanation as it gets.
                Last edited by Carld; 07-25-2012, 05:03 PM.
                It's only ink and paper

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                • #9
                  Since the subject of test questions has been mentioned I thought that some of you might like to see the final exam I used to give to my sophomores. I had these students for about half of their freshman year and all of their sophomore year for a total of 130 days in shop. Figure about one hour of theory time per day and this is what I expected them to know at the end.

                  I gave the test as open book, open notebook and Machinery's Handbook. Each year I would see grades ranging from a low of 17 one year to 100 occassionally. Some kids are just dumb and should be left behind!

                  http://neme-s.org/Final%202005.doc Questions

                  http://neme-s.org/FINALANS.doc Answers



                  I realize that some questions might be answered differently given the wide range of experience on this board but my answers are based on the text we used at the time.
                  Errol Groff

                  New England Model Engineering Society
                  http://neme-s.org/

                  YouTube channel: http://www.youtube.com/user/GroffErrol?feature=mhee

                  Comment


                  • #10
                    Originally posted by Errol Groff View Post


                    I realize that some questions might be answered differently given the wide range of experience on this board but my answers are based on the text we used at the time.
                    Number two I answered "digital and vernier",.......it was downhill after that. I don't think I even got 17 right.
                    Gary


                    Appearance is Everything...

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                    • #11
                      A mandrel has a slight taper so it wedges into the bore of the work so it can be turned between centers.
                      I'd like to add "expanding mandrel" to the list, got what I hope will be one sitting in the lathe half done right now. Have not found a good enough deal on quality between centers mandrel yet, a non-import set would be even nicer.

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                      • #12
                        I have a set of expanding arbors and a set of expanding mandrels. I bought both from Enco. The mandrels are used between centers; the arbors are held in the lathe chuck.

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                        • #13
                          Originally posted by Errol Groff View Post
                          Since the subject of test questions has been mentioned I thought that some of you might like to see the final exam I used to give to my sophomores. I had these students for about half of their freshman year and all of their sophomore year for a total of 130 days in shop. Figure about one hour of theory time per day and this is what I expected them to know at the end.

                          I gave the test as open book, open notebook and Machinery's Handbook. Each year I would see grades ranging from a low of 17 one year to 100 occassionally. Some kids are just dumb and should be left behind!

                          http://neme-s.org/Final%202005.doc Questions

                          http://neme-s.org/FINALANS.doc Answers



                          I realize that some questions might be answered differently given the wide range of experience on this board but my answers are based on the text we used at the time.


                          Question 64. If an alligator's eyes are six inches apart what is the approximate length of the beast?

                          And I thought they only taught that in Florida.
                          Doug

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                          • #14
                            I am glad to see the proper terminology explained. I hope I can remember.
                            Paul A.
                            SE Texas

                            Make it fit.
                            You can't win and there is a penalty for trying!

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                            • #15
                              Originally posted by Carld View Post
                              An arbor has a straight shank and a shoulder for the work to rest against with no taper and a nut to hold the work while it is machined or if an arbor for a cutter to hold the cutter without slipping.

                              A mandrel has a slight taper so it wedges into the bore of the work so it can be turned between centers.

                              That's about as simple an explanation as it gets.
                              About as dumb as it gets. Carl, does an arbor for a Jacobs chuck meet your requirements above? Do expanding mandrels have a taper? What would you have scored in Eroll's class?

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