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3 Jaw 6 jaw question.

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  • 3 Jaw 6 jaw question.

    I am making some parts from UHMW the part for all intents and purposes is a roller but it really isn't because when it is finished and installed it does not roll but for discussion sake I will call it a roller.

    I make 100 to 200 of these parts a month so setting up each part in a 4 jaw is out of the question and really not needed.

    I buy the material in 10' lengths. I then cut 1.25" lengths from that with a 12" wood cutting chop saw. They are somewhat like a hockey puck at this point.

    My next step is to chuck up each part in my manual lathe. In the lathe I bore a .5" hole through the center, counter bore a 1.125" diameter .75" deep then face off the part to square up on one side. These three steps are all done on one set up. I have a rotating tailstock that holds the .5" bit and the 1.125" counter bore bit.

    The material is not inherently very round or I should say perfectly round. I have been using a 3 jaw chuck to hold the work.

    After this operation I take each part and put them on an arbor I made out of Acme thread. The arbor has a tapered counter bore in one end that I use a center in that end on the tailstock and I chuck the other end of the acme thread in the 3 jaw. The end of the arbor that goes in the chuck has a turned hub with a shoulder and it is welded to the acme so it is made one piece on that end. The shoulder keeps the arbor from pushing through the jaws of the chuck when the tail stock center is tightened.

    I run 9 parts at a time on the arbor to turn them round and concentric to their bore. I end up removing a fair amount to get them round and I lose more material than I would like on the diameter to do so. The material comes over size for 4” I think this is so it can be turned to a finished 4”. The problem is before I can get them all round they are under the 4” diameter by about .025”.

    My thinking is if I had a 6 jaw chuck when making the original bore I would have a better chance at hitting the center of the material than using a 3 jaw and the result would be removing less material in the next step on the arbor what do you think?

    Thanks Mike

  • #2
    Mike,
    Use a 3 jaw chuck with removable jaws and make some soft jaws. That way you can also set the depth. A 6 jaw chuck is really not the answer for that situation. You should take a day and bring some of your parts up to Whidbey Island and I can help you with some ideas to mass produce those in your shop.
    Mark Hockett

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    • #3
      Thanks for the offer Mark but I am so busy right now I am not sure when I could get away. I ordered a CNC router table to build these parts from sheet stock but I have not recieved it yet.

      I will still be making another roller out of the same stuff and I will be in the same boat for boring the hole in the center. I do have removable 2 piece jaws on my lathe so I could make some soft jaws but I am not sure how that would help. The material is irregular for diameter and roundness. My thought was by having more jaws it would tend to center the part more than just 3 jaws. Maybe I am not thinking straight about the soft jaws would they have more surface area to hold the part making it almost like a collet?

      Comment


      • #4
        Its in how you make the top jaws

        You could make some 2 piece welded top jaws - on the face of the jaw weld a piece of rectangular bar and then bore the inside surface of the bar so you have close to 360 degrees. Here's a picture that might explain it better... (a picture is worth a thousand wordsd...)

        http://i250.photobucket.com/albums/g.../ChuckJaws.jpg

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        • #5
          I'm wondering how consistantly irregular this stuff is? Does it have a "high" consistantly along the whole length? Or is that even out of whack?
          Reason I'm asking is "if" it is sorta consistant...could you not mark the high spot along the length with a marker before cutting it...then orient these marks to a spot on your chuck with jaws that are bored accordingly?
          That would take some of the guess work out of it.
          Just an idear
          Russ
          I have tools I don't even know I own...

          Comment


          • #6
            What about using a 4 jaw chuck to true up the round stock before you cut it up into the hockey pucks. That way you could get the maximum size circle out of a lot of pieces with just the one setup. Then bore concentric to the outside.
            I'm an abstract poet and I didn't even think I was.

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            • #7
              Could make a pot chuck and use that or is the stock too irregular? A pot chuck should work about like a large collet and would let you inexpensively see if it is helpful to grip on a large fraction of the circumference - but only if the stock is round enough to get it into the pot chuck, of course.

              I recently made a pot chuck and marked it so I could always orient it the same when putting it back into the 3 jaw; the repeatability and accuracy was surprising. However, my stock was round to start with and only needed facing and an accurate center hole.

              John

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              • #8
                Originally posted by SmoggyTurnip
                What about using a 4 jaw chuck to true up the round stock before you cut it up into the hockey pucks. That way you could get the maximum size circle out of a lot of pieces with just the one setup. Then bore concentric to the outside.
                That would not work in this case the material is expensive and comes in 10' lengths. I have learned maching as a hobby and machining for $$ is a whole different animal. Everything is about time and how fast you can produce a part that is why the parts are cut in a saw and not parted on the lathe. I lose 4" of material in each 10' length I cut because as you get to the end of the stock it is hard to support and if it is not held tight it will bind in the saw and kick back.
                Mike

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                • #9
                  The main advantage of a six jaw chuck is it provides more gripping power with less deformation than a three jaw. Center is center, and it will not center substantially better than a three jaw.

                  A six jaw might average out the highs and lows, but the suggestions for top jaws or pot collets will achieve the same result at lower cost.
                  Jim H.

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                  • #10
                    Gundog, given your last post, it sounds like a good case for making a holding jig for your drop-saw. Something like a tube you can slide the stock through, with a push stick for the last coupla slices.

                    I'm all for saving $$$ but don't lose fingers!
                    Just got my head together
                    now my body's falling apart

                    Comment


                    • #11
                      I think you should face the second sides off parallel before
                      clamping the parts on the arbor.

                      Or else work as a bar and drill/c'bore/face, and then part them off.

                      Clamping un parallel parts on an arbor will randomly bend the arbor depending on the position of the parts.

                      Is the arbor center concentric with the o.d. ?

                      How far back in the chuck do you stick the parts when you do the first op.
                      Far enough to get the o.d. fairly true?

                      How square does your saw cut? I believe you will lose less material parting, than sawing them off.

                      Good Luck,

                      Kap

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                      • #12
                        be quite a lathe to get 10' of 4" + OD through the headstock, Kap
                        Just got my head together
                        now my body's falling apart

                        Comment


                        • #13
                          Originally posted by JCHannum
                          The main advantage of a six jaw chuck is it provides more gripping power with less deformation than a three jaw. Center is center, and it will not center substantially better than a three jaw.
                          The 6 jaw has less gripping power over a 3 jaw. The 6 jaws divide the PSI of the gripping force in half. The advantage of the 6 jaw is less deformation due to spreading the gripping force over more jaw area.
                          Mark Hockett

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                          • #14
                            Originally posted by Mark Hockett
                            The 6 jaw has less gripping power over a 3 jaw. The 6 jaws divide the PSI of the gripping force in half. The advantage of the 6 jaw is less deformation due to spreading the gripping force over more jaw area.
                            Hmmmm.........so by that logic, a "1 or 2 jaw" chuck would have more gripping power than a 3 jaw.

                            Personally, I would have thought the gripping pressure was a function of the mechanism that moves the jaws (i.e. scroll gear) and the surface texture of the jaws versus the surface of the part (and resistance to deformation) being held. Might be some other factors I'm overlooking, but fewer number of jaws doesn't seem logical for more grip....??

                            Maybe I'm missing something??
                            Last edited by RPease; 04-01-2008, 01:41 PM.
                            RPease

                            Comment


                            • #15
                              Its comes down to the surface area of the contact point. The larger the surface area the less PSI applied if everthing else, scroll, chuck wrench, is the same. More jaws usually mean more surface area. I know for a fact that 6 jaw chucks don't grip as well as 3 jaw chucks as I have both a 6 jaw and 3 jaw chucks for my CNC lathe. If I have the 6 jaw on the lathe I can't cut near as heavy as I can with the 3 jaw because the part will slide in the 6 jaw chuck.
                              Mark Hockett

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