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  • #31
    Connor, I'd suggest you pick a project to machine and just concentrate on one part at a time, one operation at a time. When you encounter a roadblock that requires a new tool or modification, then at that point, buy or modify. It'll be much easier for you to know what you actually need.
    If you learn to accept that a 3 jaw chuck isn't for precision and is only accurate in a single chucking, you'll be at much more ease.
    Also watch Abom79 on YouTube dial in a part on a 4 jaw chuck, and more importantly, how he checks the part and what he checks.

    Comment


    • #32
      Originally posted by Connor View Post
      ... This lathe is in a Maker Space, a community workshop with lots of people with lots of varying skills. Most don't know how to use the 4-jaw with enough confidence or patience. They just want to throw their stock in and turn it down.....
      Throw their stock in and turn it down.
      Perfect.
      Sounds to me you are allowing people with minimal training to operate a machine
      that can easily kill them without the appropriate level of seriousness and attention.

      You only need a precision chuck for re-chucking existing work to create new and
      modify existing features.

      You do not need a precision chuck for holding raw stock for new work where all
      related features are done in one chucking.

      There is a difference between need and want in the decision whether to use a
      3 jaw chuck or a 4 jaw chuck.

      If you think people (users) can not wrap their brains around a 4 jaw chuck
      what makes you think they can master a set-true 3 jaw chuck ? ? ?

      The set-true chuck is not the answer to all.
      It is not a set-it-and-for-get-it.
      The scrolls are rarely accurate at all diameters.

      What might run perfectly true chucking 1" stock is not guaranteed to have
      any runout chucking 2" stock. YOU NEED TO ADJUST IT ! ! !
      The scrolls are rarely accurate at all diameters.

      …...And a set-true chuck adjusts BACKWARDS from a 4 jaw chuck.
      That will for sure mess with the individuals who are too lazy and in a hurry
      to learn how to use a 4 jaw.

      I am not trying to rain on your parade here, just trying to manage you
      expectations with your endeavor that might not be as straight forward
      as you believe.

      --Doozer
      DZER

      Comment


      • #33
        OK, somehow I'd missed the part somewhere when you mentioned it would be in a maker space environment and used by a variety of folks. Or is that from another thread?

        Either way though I'd echo Doozer's comments that it's not a set once and then leave it. It might not even be a set once for one size given that swarf in the scroll moves around. I'd also echo that it would end up even more confusing than trying to use a proper four jaw. Especially if they needed to remember to ease firmly locked down backplate bolts before adjusting. And just as importantly to tighten them again if doing a heavier load sort of cut. That's a lot of steps to remember for folks that are occasional users.

        I assume that you don't just let anyone use the metal lathe without some basic training and safety rules. Otherwise the risk to the machine and person is rather scary to ponder. Perhaps give them a second more advanced class in lathe operations? Like how to easily and quickly switch chucks and set a four jaw to true? This is pretty basic stuff that all of us here had to learn early on in our own shops.

        A trick I use for my own shop where I just need to do a small part flipped that needs to be centered is a small four jaw on a stub held in my three jaw. The little four jaw came in a box of goodies I was given years ago. For small parts centering it's proven to be super handy and I use it more than I thought I would when I made the little stub for it.
        Chilliwack BC, Canada

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        • #34
          Originally posted by Doozer View Post

          Throw their stock in and turn it down.
          Perfect.
          Sounds to me you are allowing people with minimal training to operate a machine
          that can easily kill them without the appropriate level of seriousness and attention.
          It's not like that. Everyone has to go through a 4-5 hour auth class on how to use the machine, including safety training and machine maintenance. But, they can only absorb so much info in one sitting. I do offer advance classes for them, but to get them up and going, the 3-jaw is the easiest.

          Originally posted by Doozer View Post
          You only need a precision chuck for re-chucking existing work to create new and
          modify existing features.

          You do not need a precision chuck for holding raw stock for new work where all
          related features are done in one chucking.

          There is a difference between need and want in the decision whether to use a
          3 jaw chuck or a 4 jaw chuck.

          If you think people (users) can not wrap their brains around a 4 jaw chuck
          what makes you think they can master a set-true 3 jaw chuck ? ? ?

          The set-true chuck is not the answer to all.
          It is not a set-it-and-for-get-it.
          The scrolls are rarely accurate at all diameters.

          What might run perfectly true chucking 1" stock is not guaranteed to have
          any runout chucking 2" stock. YOU NEED TO ADJUST IT ! ! !
          The scrolls are rarely accurate at all diameters.

          …...And a set-true chuck adjusts BACKWARDS from a 4 jaw chuck.
          That will for sure mess with the individuals who are too lazy and in a hurry
          to learn how to use a 4 jaw.

          I am not trying to rain on your parade here, just trying to manage you
          expectations with your endeavor that might not be as straight forward
          as you believe.

          --Doozer
          Wohhh.. Calm down.. I'll say it again. the 3 jaw chuck was over 0.015" out. It was a passing thought that putting 4 set screws that allow me to move the chuck around on the backplate might make it a tad easier to dial in vs tapping it, and also provide a bit more stability vs just the friction of the bolts holding on the back plate since it won't be tight against the register. I'm not looking for perfect, just better than 0.015" run out.

          Comment


          • #35
            ...I'll say it again. the 3 jaw chuck was over 0.015" out.
            That's excessive for sure. But it's also indicative that the chuck is either badly worn and the jaws need grinding or that it's put together with the jaws in the wrong slots or that the insides are packed with swarf. Or possibly some previous owner (if there was one) ground the jaws poorly?

            I've never seen a three jaw in even half way decent condition that is that far out without some pretty basic reason for it. More typical is anything from 0 to .005. And even .005 is not all that common on a chuck that is in good condition and clean inside. Usually from what I've seen they are better than that.

            Perhaps get a better feel for this by checking runout of the chuck body. And even something as basic as ensuring the jaws are actually in the slots in the proper numbering. And if that's good clamp a round bar in the jaws and dial gauge the outside steps to see if the jaws are out on the outsides by the same .015? Somewhere along the way something that is responsible for the excess runout should jump out at you.
            Chilliwack BC, Canada

            Comment


            • #36
              Originally posted by BCRider View Post

              That's excessive for sure. But it's also indicative that the chuck is either badly worn and the jaws need grinding or that it's put together with the jaws in the wrong slots or that the insides are packed with swarf. Or possibly some previous owner (if there was one) ground the jaws poorly?

              I've never seen a three jaw in even half way decent condition that is that far out without some pretty basic reason for it. More typical is anything from 0 to .005. And even .005 is not all that common on a chuck that is in good condition and clean inside. Usually from what I've seen they are better than that.

              Perhaps get a better feel for this by checking runout of the chuck body. And even something as basic as ensuring the jaws are actually in the slots in the proper numbering. And if that's good clamp a round bar in the jaws and dial gauge the outside steps to see if the jaws are out on the outsides by the same .015? Somewhere along the way something that is responsible for the excess runout should jump out at you.
              I have a feeling that this chuck wasn't originally part of this machine. The backplate register has run out, and the face is out a bit too. I torn the chuck apart and cleaned it along with the jaws. I'm going to double check the runout on the surface of the spindle and make sure it's running true. (The spindle itself is good).

              I'm then going put the backplate on, and check it in each of the 3 possible positions it can be in. I know that can affect it too. If the backplate still isn't true, I'll face it off, and turn a new register and reinstall the chuck.

              I don't see any signs that the jaws have been ground in place.

              I really think it was either a chuck for a different machine. The swapped backplates. They really did a piss-poor job marrying the backplate to the chuck. or a combination of them all.

              Comment


              • #37
                I'd go with a piss poor job of marrying the backing plate if I were a betting sort. When you're done with your good solid "back to basics" plan to dress the backing plate I'd be surprised if the chuck isn't well within a reasonable runout.

                I'm as guilty as the next for letting my mind run off with all manner of "what if's" at the drop of a hat. A trait that shows up in my jumping around with different suggestions in threads such as this. And 99% of the time when the dust settles some lower level KISS problem and correction turns out to be the cause and solution. Your plan to go back to the basics will likely fix things up just dandy. But I would start out with a careful inspection of the backing plate seat on the spindle to be sure that any dings and raised burrs are not holding it out of position as a starting point of this "back to basics" approach... That's assuming you didn't closely look at it already.

                The other Connor was chasing down a chuck runout too. And found that his big runout was due to a bit of swarf mashed down flat on the register surface of his threaded spindle nose. It's often those little things....
                Chilliwack BC, Canada

                Comment


                • #38
                  Originally posted by Connor View Post

                  I have a feeling that this chuck wasn't originally part of this machine. The backplate register has run out, and the face is out a bit too. I torn the chuck apart and cleaned it along with the jaws. I'm going to double check the runout on the surface of the spindle and make sure it's running true. (The spindle itself is good).

                  I'm then going put the backplate on, and check it in each of the 3 possible positions it can be in. I know that can affect it too. If the backplate still isn't true, I'll face it off, and turn a new register and reinstall the chuck.

                  I don't see any signs that the jaws have been ground in place.

                  I really think it was either a chuck for a different machine. The swapped backplates. They really did a piss-poor job marrying the backplate to the chuck. or a combination of them all.
                  Well if the backplate register has runout and so does the face, thats your answer isn't it? Is this a D1-3? Make sure the taper is really, really clean. When I'm installing one, I lightly tighten the cams, tap the face on the chuck a few times with a rawhide hammer, to make sure its all seating, then finally tighten. If that doesn't work, and its the same runout at the same place each time, then re-machine the backplate register and face.
                  'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

                  Comment


                  • #39
                    Originally posted by BCRider View Post
                    If you do this do it with four set screws at quarter circles apart so it acts like you're centering a four jaw. Otherwise trying to chase down centering with three screws will drive you bonky.

                    The setup also only works if you have clear access to the bolts on the backplate that hold the chuck to the backplate.

                    You also still need a dial gauge to zero in the item.

                    In a previous post in your other thread you posted pictures of the clamping edges of your jaws. Regardless if you modify the backplate and chuck to allow for centering or not the jaws are begging to be re-ground to remove the bell mouthing from the wear they have tolerated over the years. And if you do that right you might well find that you restore centering to something like a thou or thou and a half. And for most things that's pretty good. And for the rest you have four jaws.

                    No four jaw independent with the lathe goodies? You'll want one anyway to hold any number of oddball items at some point. And if you have a four jaw independent then you can center stuff really quickly anyway.

                    So while it's your time and lathe I vote for grinding the jaws of your 3 jaw and buy a 4 jaw to use with the lathe alongside the 3 jaw.
                    You think 3 is bad. Our Buck 6 jaw 'adjust-tru' has 6 adjusters. Six. It's not as bad as it sounds, but 4 would be a lot more logical.
                    21" Royersford Excelsior CamelBack Drillpress Restoration
                    1943 Sidney 16x54 Lathe Restoration

                    Comment


                    • #40
                      My bisons have 4, but the are not at 90 degrees to each other, so adjustments are not as simple, but you get used to it.

                      My favorite chuck is a Rohm 4-jaw with both independent jaw adjust plus scroll. That's my "go to" for precision and often just stays for months the lathe for all work.

                      Comment


                      • #41
                        So, confession. I borked up the original backplate.. more than once. Ended up making it too thin, etc etc.. I ordered a replacement and turned the register down to a slip fit. Faced it off etc etc. I did have to enlarge the ID of the mounting holes for clearance as this plates bolt hole pattern was slightly smaller than that of the chuck. After cleaning the chuck (inside and out) and the jaws and remounting the backplate, I ended up with .0045" TIR. I swapped the jaws around in each position. (after marking them with the first reading) and couldn't ever obtain anything better than .0045" With the jaws back in the original position ended up with .005-006 TIR, not the original .0045" I even went so far as to torque the backplate bolts all to 20lbs. I was testing using a .5" edge finder shank. I'm not sure if I should turn the register down by 1.5 thou or so, and loosen the bolts up and try to tap it in to get better results or not. What's the ramifications of not having it on the register? What would be an acceptable TIR for a 3 jaw chuck?

                        Comment


                        • #42
                          Originally posted by Connor View Post
                          ........... I'm not sure if I should turn the register down by 1.5 thou or so, and loosen the bolts up and try to tap it in to get better results or not. What's the ramifications of not having it on the register? What would be an acceptable TIR for a 3 jaw chuck?
                          The worst that can happen is the chuck shifts on the backplate and TIR increases but that would likely only happen if you crashed your lathe. If you are going to turn it down, turn it down (on radius) at least half the TIR; that way you can get your chuck to be quite accurate at the diameter you tested it at and it won't hurt a thing if you go a little smaller than that even.

                          Asking what would be an acceptable TIR for a 3 jaw chuck is kind of like asking how high is up. For some/most things it doesn't matter but if it really matters, you need a four jaw or you need to modify your backplate and readjust your chuck so TIR is as low as you can get it for the diameter you are chucking up on.
                          Location: Saskatoon, Saskatchewan, Canada

                          Comment


                          • #43
                            4.5 thou isn't great. And if it was 4.5 thou consistently over a range of sizes then I have to admit that I'd be sorely tempted to trim the register a bit with a file on the one side only to cut it down to more like a couple of thou. By using a file to slightly "eggify" the register and perhaps make some raised center punch marks on the other "low" side to pull it over a bit I'd avoid creating a loose situation that might come back to haunt me later.

                            But before I did that I'd run the indicator on a wide range of work in the jaws from as small as 1/4" up to whatever the chuck will hold with just two full turns of the scroll still holding the jaws in place... my personal maximum tolerable extension. And from that see if the runout is consistent or it's only for the one size and changes over a range of sizes and if the high point stays in the same place or if it runs around based on the "clock position" of the scroll or not. You might fix one particular diameter but something that is only 1/16 to 1/8 bigger might be out by a lot more in a different direction due to the "fix".
                            Chilliwack BC, Canada

                            Comment


                            • #44
                              Originally posted by Connor View Post
                              I was testing using a .5" edge finder shank. I'm not sure if I should turn the register down by 1.5 thou or so, and loosen the bolts up and try to tap it in to get better results or not. What's the ramifications of not having it on the register? What would be an acceptable TIR for a 3 jaw chuck?
                              I would not change the backplate till you try a few different diameters to see if the TIR stays the same or not. If the TIR is the same at 1/2 inch, 1 inch and 2 inches then chances are your scroll is OK. If it changes (and in different directions) then your scroll is not consistent will be constantly re-centering each time you put stock in the chuck.

                              I would be worried about the chuck shifting if it does not have contact with the register. The Set-tru style gets away with it because the adjusting screws bear against the register from several angles.

                              Dan

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

                              Comment


                              • #45
                                So many people worry about the chuck moving if the register is not tight. They have obviously never tried it in real life, there are so many theorists out there giving advice.
                                I use about five chucks all with backplate registers reduced by about 0.020" especially to enable a little adjustment. The fixing bolts have to have enough play as well. The larger chucks have an additional three bolts which is easy to achieve with a scroll chuck. Just think of how the workpiece is held onto a mill bed, nothing but friction, no register and mostly interrupted cuts. There is never a worry about that is there?

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