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  • Question For Forrest or other "real Machinist."

    My Rohm chuck came in yesterday. I have a backing plate to mount it onto.

    It has a recess a smaller diameter than the faceplate. I only have "one" faceplate so I don't want to screw it up. I (question) need cut cut the face to (A) just shoulder fit into the hole, then drill the holes, OR (B) cut shoulder just exactly deep enough to bottom out inside the chuck then drill the holes?

    I have the L00 Mount chucked up and running sqare in the 3jaw.. I need to mount it in thou don't I instead of in the chuck. I should remove the old chuck and attach the faceplate directly?
    To me that makes more sense since I would not have any error in the 3jaw translated and multiplied to the 4jaw mount.

    SO? before I turn a chip, do I need to cut just a shoulder or a exact one to bottom out?

  • #2
    the way i mount the chucks is firt mount the plate to the spindle not in a chuck that way you dont have run out adding up. then i cut about .125 shoulder to slip in chuck. then drill and tap holes. then you are on your way.
    you are right about putting it on the spindle. and the error adding up if you do it in chuck.

    Comment


    • #3
      I don't know if I'm considered "a real machinist" but I was payed to be one for almost thirty five years.The only way I've ever done the "new chuck" setup is to mount the backing plate on the spindle first.True the backing plate to the spindle.If a recess is required don't make it project to the point of interfering with the chuck.1 or 2 thousandths between the plate and the chuck should keep things nice.Take measurements often.It's hard to add material back once you've removed it.I wish you luck with your Rohm.I mounted a 12 1/2" on the Hendey I have.The chuck cost more than the lathe.It's okay but it doesn't repeat well on stock under 1".Anything over that and it does just fine.I'd really like to find an 8"or10" 3 jaw for the L1 mount and do away with this large chuck.

      Comment


      • #4
        Here's what you need to know. Be aware, this may turn into a pissing contest.
        Have fun,
        Ed

        http://www.lathes.co.uk/latheparts/page7.html
        Ed Pacenka

        Comment


        • #5
          Thanks.. I will cut the faceplate tomorrow when Hopefully I am feeling better.

          I got too hot today, moving things around again making room for a new multi-tool. Hard to walk with a pup hitting you in the back of the knee with a toy to throw. I have neglected him while laying in the house sick. Like a kid he wants to make up for it in one day.

          1 or 2 thou, who are you talking to? HA.. If I hit it within a thou I am happy. As a machinist I am a good electrician. I try thou.

          Comment


          • #6
            Hello
            I have a friend who has more than seventy years experence and he says that three jaw chucks were never intended for better than three to five thou accuracy. He only uses a four jaw.
            re
            Herm Williams

            Comment


            • #7
              <font face="Verdana, Arial" size="2">Originally posted by Herm Williams:
              Hello
              I have a friend who has more than seventy years experence and he says that three jaw chucks were never intended for better than three to five thou accuracy. He only uses a four jaw.
              re
              </font>
              I'm guessing he never used a Buck Adjust-Tru chuck.

              Ed Pacenka

              Comment


              • #8
                <font face="Verdana, Arial" size="2">I'm guessing he never used a Buck Adjust-Tru chuck.</font>
                As nice as they are, they still don't come close to the performance of soft jaws.

                Harold

                Comment


                • #9
                  You guys who make favorable comparisons of 3 jaw chucks over 4 jaws for accuracy don't know what you're taking about. Three jaw chucks are good until the first major wreck. Even the best adjust-true chuck will not hold work straight if the scroll is deformed to the body distorted.

                  I've used three jaws all my working life and among them were Cushman heavy duty three jaws chucks costing 4 times as much as Buck's finest.

                  My three jaw still holds concentricity to 0.002" but I take it off and use a 4 jaw for accurate work. How accurate you say. I call accurate when I have to warrant 0.002" concentricity of all features on a finished part.

                  Many jobs respond well to soft jaws but your jaw prep and your work's second op reference diameter has to be right on the money. I used soft jaws a lot when I ran a lathe im my younger days. Can't beat them for all-diameter work if you have more than three parts to make.

                  I keep telling you newer guys that once you get some practice in it takes less than a minute to dial in a simple diameter on a 4 jaw. If you have to pad the jaws and make the best of reference diameters and faces that won't quite agree then you can take as long as ten minutes.

                  If I had my way (by cracky!) you guys wouldn't get to use a 3 jaw until you've mastered a 4 jaw and used it for a full year (home shop; two months in a production shop) on all classes of work.

                  [This message has been edited by Forrest Addy (edited 09-10-2005).]

                  Comment


                  • #10
                    I agree with Forrest,to a point.
                    You should know how to use a four jaw chuck as a machinist. It is not nessassary as a HSM unless you need to know how to use one.
                    The average HSM doesnt need .002 acuracy,but sometimes needs to do escentric work.It never hurts to know it.
                    IMHO

                    ------------------
                    The tame Wolf !

                    Comment


                    • #11
                      egpace's link was about how i was trying to say to do it. only they do abetter job of it.

                      my first lathe i bought at an auction with no chucks. i bought a new 4 jaw from sears and used that for 6 years. then i got around to a 3 jaw.

                      Comment


                      • #12
                        Odd. I'd use a 4 jaw anytime for concentric boring etc......

                        I would NOT usually use one for eccentric work....

                        Beyond a certain amount of eccentricity, and depending on the diameter of the work, the "side" jaws are not hitting the work even partly centered. So they either get in a bind, or push the work oddly... hardly better than a 2 jaw chuck.

                        For small amounts of eccentrcity, or large sized work, etc, its OK.

                        But as for HSM's not needing a 4 jaw? Eh?

                        Someone mebbe needs to see what sort of things HSMs around the country and world actually do.... Quite a bit of their work is nicer than a run-of-the-mill commercial shop, they want it perfect if possible, which a shop don't get paid to do.

                        [This message has been edited by J Tiers (edited 09-11-2005).]
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          I have 3 jaw, 4 jaw and a lovely multibore collet chuck set that goes from 1/8 to 2".
                          Each has it's place.

                          Charles

                          Comment


                          • #14
                            "...if the scroll is deformed to the body distorted"

                            Forrest,

                            Yes, I agree, bad 3 jaw chucks can't compare to good 4 jaw chucks. For that matter, they don't fair well against good 3 jaw chucks either.

                            It's obvious the reason they both still exist is because of their unique capabilities.

                            I fully understand the benefits of a 4 jaw chuck over a three jaw. It was explained to me by my Dad in somewhere back in the 50's, and put into practice by me soon after. If I was limited to only one chuck, it goes without saying, it would be a 4 jaw.

                            I balked over the statement...

                            "never intended for better than three to five thou accuracy."

                            The Buck Adjust-tru chuck, and other adjustables, by design, were created to overcome this liability.

                            I just didn't like the thought of someone walking away with the impression that 3 jaw chucks could not be used for parts requiring better than "three to five thou accuracy". It's just not true.

                            Ed
                            Ed Pacenka

                            Comment


                            • #15
                              Forrest said:
                              <font face="Verdana, Arial" size="2">Many jobs respond well to soft jaws but your jaw prep and your work's second op reference diameter has to be right on the money.</font>
                              That forces the operator to learn good machining practices and improves skill levels tremendously.

                              <font face="Verdana, Arial" size="2"> I used soft jaws a lot when I ran a lathe im my younger days. Can't beat them for all-diameter work if you have more than three parts to make.</font>
                              Yep! All true-----except for the three parts. I've been known to machine soft jaws for one item, which, in the long haul, is more economical that fighting a setup. Soft jaws lend themselves to holding objects that otherwise are difficult to hold, let alone to get running true. I offer a washer shape as an example. Soft jaws that have been properly bored will hold the object true within a half thou easily, and not mark or distort the object. You could spend a half hour dialing in such a piece in a 4 jaw and end up with junk in spite of your efforts.

                              All chucks have a place. I wouldn't want to be without a three, or a four jaw chuck.

                              Harold

                              [This message has been edited by Harold_V (edited 09-10-2005).]

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