Announcement

Collapse
No announcement yet.

Modify 3 jaw chuck.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Modify 3 jaw chuck.

    I was wondering if anyone every modified a 3-jaw chuck (with backplate) so that you could dial it in a bit better.

    I'm thinking of taking my chuck, drilling 4 holes on the back edge of the chuck and tapping them for set screws. Turning down the boss on the back plate a bit, and putting it back together. My though is, that we could snug up the 3 cap screws, and use the 4 set set screws pushing against the boss on the backplate to dial the chuck in similar to how you would dial in a 4 jaw. After you dial it in, tighten up the 3 cap screws and double check everything. I think this similar to how "adjust-tru" chucks work, but, I'm not sure, I've never used one.

    Thoughts anyone?

    My ONLY concern would be for those set screws working their way loose and turning into miniature projectiles.

    Thanks, Connor

  • #2
    Many people have done that. I have a chuck that works just like that. I documented it in a thread on here. It's a well made chuck with a very good scroll. I dialed it in with a 1 inch bar. It's been spot on (less than .001 TIR) at every diameter that I've used since then.

    Beware: With a cheap or worn chuck the scroll is likely to have an irregular spiral, so what is perfect for one diameter may be WAY off when you use a different size work. The idea of the Set-true design is to allow you to do production runs of the same sized stock without needing to dial it in each time.

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

    Comment


    • #3
      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.
      Chilliwack BC, Canada

      Comment


      • #4
        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.

        ...........
        If you get some stiff Belleville washers, you can tighten the hold-down screws to compress them halfway. That will still let the chuck move around, and will not require tightening down when position is reached. At McMaster, you can see the compression force for the size you need. If put together "nesting together", the force adds up, so two have double the net force, three have triple, etc, up to whateve you consider needed.

        Nyloc nuts would be a good plan to prevent loosening.
        1601

        Keep eye on ball.
        Hashim Khan

        Comment


        • #5
          Originally posted by danlb View Post
          Many people have done that. I have a chuck that works just like that. I documented it in a thread on here. It's a well made chuck with a very good scroll. I dialed it in with a 1 inch bar. It's been spot on (less than .001 TIR) at every diameter that I've used since then.

          Beware: With a cheap or worn chuck the scroll is likely to have an irregular spiral, so what is perfect for one diameter may be WAY off when you use a different size work. The idea of the Set-true design is to allow you to do production runs of the same sized stock without needing to dial it in each time.

          Dan
          It's a Yamakawa chuck, made in Japan. I think it's pretty decent. I just don't think they married it up correctly with the back plate.

          Comment


          • #6
            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.
            That was the plan.

            Originally posted by BCRider View Post
            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.
            Not a issue, plenty of clearance for a allen key and plenty of dial gauges..

            Originally posted by BCRider View Post
            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.
            I don't think this was me. The jaws on the chuck look good.

            Originally posted by BCRider View Post
            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.
            Didn't come with a 4 jaw, but I did pickup a cheaper Chinese one, D1-4 integrated, so no backplate to deal with. But, the 3 jaw was 0.015" out, so, clearly needs some attention.

            Comment


            • #7
              Originally posted by J Tiers View Post

              If you get some stiff Belleville washers, you can tighten the hold-down screws to compress them halfway. That will still let the chuck move around, and will not require tightening down when position is reached. At McMaster, you can see the compression force for the size you need. If put together "nesting together", the force adds up, so two have double the net force, three have triple, etc, up to whateve you consider needed.

              Nyloc nuts would be a good plan to prevent loosening.
              I'm not sure I follow. It's a D1-4 Chuck, so, no access to the mounting studs.

              Comment


              • #8
                I've never seen real value in set-tru style chucks. You can set them up perfectly at one diameter setting but
                as soon as you clamp on a different diameter you can still have runout because of variations in the scroll.
                Same thing applies If you grind the jaws; they'll be good at one point only and off at other positions. If you
                really need to be that accurate use a 4-jaw, machinable soft jaws or a collet chuck...
                Keith
                __________________________
                Just one project too many--that's what finally got him...

                Comment


                • #9
                  Originally posted by LKeithR View Post
                  I've never seen real value in set-tru style chucks. You can set them up perfectly at one diameter setting but
                  as soon as you clamp on a different diameter you can still have runout because of variations in the scroll.
                  Same thing applies If you grind the jaws; they'll be good at one point only and off at other positions. If you
                  really need to be that accurate use a 4-jaw, machinable soft jaws or a collet chuck...
                  i keep seeing posts like this but, at the current time you can find a 3 jaw scroll chuck on ebay for approximately 3 hours of labor for the work the chuck is good for.. what's your time worth. buy a 4 jaw independent or buy a new 3 jaw scroll chuck with removable jaws so you can make your own soft jaws.

                  one way to fix concentricity errors is to tap on the most eccentric jaw with a hammer while you tighten the chuck, you might be able to make most of the error disappear.

                  Comment


                  • #10
                    Well, at least take the chuck off the back plate and run a DTI to check the axial runout and the runout on the face, if it's suspect. But before you do that, ensure the mating surfaces are clean, burr free, etc. Also try different mounting positions til you find the most accurate one and mark it.
                    Because you're new, what ever you do, do NOT modify the chuck, just in case.

                    Comment


                    • #11
                      Did what you're suggesting but in reverse on my mini lathe. Instead of modifying the chick, I skimmed a few thou off the register on the spindle flange, now when I put on whichever Chuck I can lightly snug the bolts, then tap everything into line. Works pretty well, so your idea should as well and be a lot more elegant while you're doing it

                      Comment


                      • #12
                        I modified a chick once. Ended up having to marry her.---
                        Brian Rupnow

                        Comment


                        • #13
                          Originally posted by brian Rupnow View Post
                          I modified a chick once. Ended up having to marry her.---
                          .... aand Brian wins the Internet today !!!

                          Comment


                          • #14
                            Originally posted by Connor View Post

                            I'm not sure I follow. It's a D1-4 Chuck, so, no access to the mounting studs.
                            The idea is that the chuck is on a backplate, which is why you can do the adjusting. The screws that hold the chuck to the backplate cannot be torqued very tight if you intend to adjust it. So the alternative, if you can fit them in, is to put the Belleville spring washers on those screws, to develop clamping force without "freezing" the chuck in place. Stiff ones will still allow the screws to push it around, but keep cutting forces from tilting it.

                            With your chuck, you may have the screw heads accessible from the front, which lessens the necessity for the spring washers, and may also leave no room for them.

                            I have a Buck version of that system, and I was able to get the screws just tight enough to work OK. That may be a possibility for you if the spring washers are not. Or just slack them off a bit when you need to adjust.

                            It seemed that your issue was that you had no access to the screws that mounted the chuck to the plate, so slacking and re-tightening was not possible for you.

                            Cam-loc pins are set to the appropriate position and left, they are not a factor in the adjustment you desire.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              you can do the same thing with less effort by turning down the center register of the backplate (that the chuck centers on) a wee sniff and then gently tapping it true with a mallet while the screws are lightly snugged down. Works well, doesn't take long. "Tap-tru" doesn't sound as fancy as "set-tru", but its's a lot easier

                              Comment

                              Working...
                              X