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What do you look for when buying a used 4-jaw chuck?

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  • #16
    Thanks guys - and big thanks for the Vertex recommendation. Like I said, I've not had to buy a chuck before so I'm not familiar with the current offerings. Always good to know about other mid-tier brands that, as Wierdscience says, threads the price/quality needle.

    I wound up buying an 8" 4-jaw Cushman chuck for $100. One piece jaws and covered in a patina of grime but otherwise seemed to be in great shape. A little hard to tell just how much slop there is since the grime made things sticky but the body and jaws look pristine. No signs of cracks in the screw sockets or tracks. Jaws look almost new. Should be a good fit for my 10EE.

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    • #17
      Originally posted by J Tiers View Post

      That is an odd statement. If you avoid 4 jaw chucks for whatever it is that you call "tilt", you would seem to be "avoiding drinking liquids because they sometimes spill". The 4 jaw chucks are an essential and often used tool, in my opinion. An opinion I would suspect a majority share.

      But, whatever floats your watch........
      its a "cultural" thing. you wont see many 4-jaws in europe (although i would be hard to really substantiate that). people prefer good 3-jaws. "dialing in" a 4-jaw is whishfull thinking because it only happens a one point of the piece you work on. (please dont tell me about taking a hammer to it.) 3-jaws are in no way immune to tilt, but a good chuck will have less. and statements like "3-jaws never run true" i find strange. yes, your chinese or some beat up chuck doesnt. my 250 mm forkardt has 20µ tir 8" out on a 30 mm 2/3µ test rod, provided i take care chucking it up.

      now lets have a look at that: take a piece of free machining steel and turn it true. take out the millimess, mikrocator or similar and measure runout as turned. you will come up with around 10 µ. so half of my 20 µ are the bearings, 3µ is the test bar. see, how much closer to perfect do you want to get?

      the chuck is like tires on a car. shietty tires shietty handling.

      btw, there is another problem with 4-jaws: clamping pressure. its not consistent if you mess with the individual jaws. you never know how tight the work really is.

      Comment


      • #18
        Originally posted by dian View Post

        its a "cultural" thing. you wont see many 4-jaws in europe (although i would be hard to really substantiate that). people prefer good 3-jaws. "dialing in" a 4-jaw is whishfull thinking because it only happens a one point of the piece you work on. (please dont tell me about taking a hammer to it.) 3-jaws are in no way immune to tilt, but a good chuck will have less. and statements like "3-jaws never run true" i find strange. yes, your chinese or some beat up chuck doesnt. my 250 mm forkardt has 20µ tir 8" out on a 30 mm 2/3µ test rod, provided i take care chucking it up.

        now lets have a look at that: take a piece of free machining steel and turn it true. take out the millimess, mikrocator or similar and measure runout as turned. you will come up with around 10 µ. so half of my 20 µ are the bearings, 3µ is the test bar. see, how much closer to perfect do you want to get?

        the chuck is like tires on a car. shietty tires shietty handling.

        btw, there is another problem with 4-jaws: clamping pressure. its not consistent if you mess with the individual jaws. you never know how tight the work really is.
        What do you do when turning an odd shaped part or turning an eccentric part of a shaft? I keep 4 jaws specifically for the cases where I need to turn a feature that is not concentric with the feature that I can grip in a chuck.

        Clamping pressure argument doesn't fly with me. I've never had a part slip in a 4-jaw chuck. If you can't judge how tight your grip as you tighten turn the chuck key, you have no business operating a lathe...

        I use 3-jaws all the time. I also use 4-jaws all the time. They each have their place.

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        • #19
          I only have a 6 and 8” 4 jaw, don’t posses a 3 jaw, did have one hardly ever used it, I got used to 4 jaws as all the lathes in work were 4 jaw, never saw 3, was told if you can’t use a bloody 4 jaw you have no earthly business standing in front of a lathe by a Fred dibnah clone, amusing to be honest, practically nothing in a steel plant would fit in 3, if it was small enough the OD would be covered in lumps, the technicians shop had a small selection but little bolts and widgets was their bread and butter, not big gnarled tree trunks
          i would like a six jaw but nothing seems to come up that doesn’t require selling the internal organs
          mark

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          • #20
            Originally posted by dian View Post

            its a "cultural" thing. you wont see many 4-jaws in europe (although i would be hard to really substantiate that). people prefer good 3-jaws. "dialing in" a 4-jaw is whishfull thinking because it only happens a one point of the piece you work on. (please dont tell me about taking a hammer to it.) 3-jaws are in no way immune to tilt, but a good chuck will have less. and statements like "3-jaws never run true" i find strange. yes, your chinese or some beat up chuck doesnt. my 250 mm forkardt has 20µ tir 8" out on a 30 mm 2/3µ test rod, provided i take care chucking it up.

            now lets have a look at that: take a piece of free machining steel and turn it true. take out the millimess, mikrocator or similar and measure runout as turned. you will come up with around 10 µ. so half of my 20 µ are the bearings, 3µ is the test bar. see, how much closer to perfect do you want to get?

            the chuck is like tires on a car. shietty tires shietty handling.

            btw, there is another problem with 4-jaws: clamping pressure. its not consistent if you mess with the individual jaws. you never know how tight the work really is.
            A worn 3 jaw may not center up. A worn 4 jaw always will until it ceases to function at all. There you have a slight suggestion about why one might want a 4 jaw chuck, and might never need a 3 jaw.

            I will point out that ALL your 3 jaw chucks are "worn", if you have used them. So ALL of them are working their way toward being unable to center up well.

            A NEW 3 jaw has a centering error. Do not attempt to say it does not, because you are just wrong. Nothing is perfect. But a 4 jaw can be centered to whatever degree your skill and measuring tools allow.

            If "dialing in" a 4 jaw is wishful thinking, then a centered part in a 3 jaw is equally wishful thinking. Both hold with jaws that run in slots in the chuck, so both have exactly the same issues with "tilt". Thinking that somehow a 3 jaw does not have that problem is REALLY "wishful thinking".

            What kind of "magic" makes a 3 jaw perfect without tilt, while a 4 jaw always has such a problem (in your thinking).

            Clamping pressure? What planet do you live on? The 4 jaw is the chuck that will give any amount of clamp pressure reliably. Obviously you have never read one of Forrest Addy's posts on achieving the "death grip" with a 4 jaw.

            Dian, it seems that pretty much all the points you made are based on bad information. You might want to reconsider.

            2801 3147 6749 8779 4900 4900 4900

            Keep eye on ball.
            Hashim Khan


            It's just a box of rain, I don't know who put it there.

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            • #21
              I was going to run all these issues up the flagpole and probably be perceived as a dick for doing so,
              but Jerry described exactly what I was thinking. Thanks for taking the hit for me
              I do want to add, that for workpieces longer than they are flat...
              Tapping in the long end with a mallet for center aim is pretty standard procedure.
              If your part is a foot long, there is no way around indicating the far end.

              --Doozer
              Last edited by Doozer; 05-03-2021, 12:59 PM.
              DZER

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              • #22
                i knew the hammer would show up. (you need worn jaws for that to even marginally work.) jerry, did you actually read what i said? and the "bad information" is based on 30 years of shop experience.
                Last edited by dian; 05-03-2021, 01:21 PM.

                Comment


                • #23
                  Originally posted by dian View Post

                  its a "cultural" thing. you wont see many 4-jaws in europe (although i would be hard to really substantiate that). people prefer good 3-jaws. "dialing in" a 4-jaw is whishfull thinking because it only happens a one point of the piece you work on. (please dont tell me about taking a hammer to it.) 3-jaws are in no way immune to tilt, but a good chuck will have less. and statements like "3-jaws never run true" i find strange. yes, your chinese or some beat up chuck doesnt. my 250 mm forkardt has 20µ tir 8" out on a 30 mm 2/3µ test rod, provided i take care chucking it up.

                  now lets have a look at that: take a piece of free machining steel and turn it true. take out the millimess, mikrocator or similar and measure runout as turned. you will come up with around 10 µ. so half of my 20 µ are the bearings, 3µ is the test bar. see, how much closer to perfect do you want to get?

                  the chuck is like tires on a car. shietty tires shietty handling.

                  btw, there is another problem with 4-jaws: clamping pressure. its not consistent if you mess with the individual jaws. you never know how tight the work really is.
                  I use good 3/6 jaws regularly. One dialed into <20 micron at any grip range with ID or OD jaws, I don't know about at 8" out, I don't particularly care. The other has been dialed even tighter. I do use them for a lot of round work when working on a smaller machine. I still use 4 jaws, a lot. Not much on that lathe, as it is primary a second op machine. However, new stock in large diameters isn't round. So to get the truest running, you have to sit there and try it in multiple spots. That's some BS. Nobody is spinning around 250 lb bars in their lathe. It's always the 4 jaw that is used for roughing in big stock.

                  Originally posted by Fasttrack View Post
                  Clamping pressure argument doesn't fly with me. I've never had a part slip in a 4-jaw chuck. If you can't judge how tight your grip as you tighten turn the chuck key, you have no business operating a lathe...
                  Agreed. Especially a tooth-y chuck like a Cushman. Even on relatively smooth jawed chucks I've never had a part come out. I'm also not sure what he means by not being able to judge pressure. When I can no longer turn a 16" chuck key with all my force.... well it's pretty tight. And if I need more, I got a cheater bar. Acme threads per jaw impart a lot more force than scrolls running all 3/4/6.

                  Originally posted by Doozer View Post
                  I was going to run all these issues up the flagpole and probably be perceived as a dick for doing so,
                  but Jerry described exactly what I was thinking. Thanks for taking the hit for me
                  I do want to add, that for workpieces longer than they are flat...
                  Tapping in the long end with a mallet for center aim is pretty standard procedure.
                  If your part is a foot long, there is no way around indicating the far end.
                  I told ya Jerry is right sometimes!

                  Originally posted by dian View Post
                  i knew the hammer would show up. (you need worn jaws for that to even marginally work.) jerry, did you actually read what i said? and the "bad information" is based on 30 years of shop experience.
                  So you've never bumped a part in? Yes it does require worn jaws unless you hold it out on the end. Doing so the runout is mild enough that the chuck can deform the part into seating on the jaws. That is why folks rough with cushman chucks and the like. They clamp a part loosely, dial in the near end, bump the far end in, go back and forth if required, then tighten the jaws up, sinking the teeth in, preventing the part from moving or rocking while still having even pressure. I have to seriously doubt your skills as a machinist if you've never bumped a part in.

                  And regarding years of experience, there is probably 100+ in the 5 folks disagreeing with you.

                  Lastly, chuck this with your precious 3 jaw.

                  Click image for larger version

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                  21" Royersford Excelsior CamelBack Drillpress Restoration
                  1943 Sidney 16x54 Lathe Restoration

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                  • #24
                    Originally posted by dian View Post
                    ,,,,,,,,,,, jerry, did you actually read what i said? and the "bad information" is based on 30 years of shop experience.
                    Yes I did.

                    I have to say, it sounds more like ONE year of shop experience, repeated 30 times.......

                    I do not understand how a person can get good results rechucking a part in a 3 jaw, vs putting it in a 4 jaw and getting it done right. The irregular parts, square parts etc are also very good points, try THAT in your 3 jaw, and get the part centered...... not gonna happen.

                    I DO have one 3 jaw chuck that I trust to center a part perfectly. It is an "adjust-tru", made by Buck Chucks. It has 4 adjusting screws to center the work with, after the work is secured in the chuck by the 3 jaws. THAT can be centered like a 4 jaw.

                    And you may want to obtain a steady rest, for those very long parts where the runout worries you so much.

                    Hey, I answered your question, after this your opinion is your opinion, although I would not advise anyone taking it seriously, and you can work however you like. You will just have to forgive me if I do not take your advice. YMMV, whatever floats your watch.

                    2801 3147 6749 8779 4900 4900 4900

                    Keep eye on ball.
                    Hashim Khan


                    It's just a box of rain, I don't know who put it there.

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                    • #25
                      I count the jaws, if there are 4 it is good.
                      I will be here all week, don't forget to tip the bartender.

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                      • #26
                        Originally posted by dian View Post
                        i knew the hammer would show up. (you need worn jaws for that to even marginally work.) .
                        Are you freakin high? I mean seriously.?
                        What do the colors taste like in your reality.?

                        -D
                        DZER

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                        • #27
                          Originally posted by The Metal Butcher View Post
                          ...

                          Lastly, chuck this with your precious 3 jaw.

                          Click image for larger version

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                          This is a college kid that figured out this setup.
                          Just for the record

                          -Doozer

                          DZER

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                          • #28
                            Originally posted by The Metal Butcher View Post

                            That's some BS. Nobody is spinning around 250 lb bars in their lathe.
                            I routinely place 250+ Lb parts in a 3 jaw chuck (-:



                            Last edited by Bented; 05-04-2021, 07:43 PM.

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                            • #29
                              Aight, fair enough. Can't argue with that.
                              21" Royersford Excelsior CamelBack Drillpress Restoration
                              1943 Sidney 16x54 Lathe Restoration

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                              • #30
                                That deal about "bumping in" a part...... I've done it too, but I never quite feel right about it.... If I can move the part, I sure figure the force of the cut can move it too, especially if there gets to be any chatter, etc.

                                And if I tighten things, the part moves again, and needs re-bumping, to same situation. It "works" but always seems, as a co-worker used to say, "a bit leaky".
                                2801 3147 6749 8779 4900 4900 4900

                                Keep eye on ball.
                                Hashim Khan


                                It's just a box of rain, I don't know who put it there.

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