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  • 3 jaw chuck problems

    Hi all,

    I am having problems with the accuracy of my three jaw chuck. The chuck came with the Lathe (Jet 1340) and is showing about .003 tir. I think this is about as good as it is going to get with this chuck. I am still working with my 4 jaw, but what a pain. I understand the adjustable 3 jaw chucks can be dialed in to .0005 tir. I am considering the one from Enco or possibly a Phase II. I think the Buck/Bison may be out of my price range.

    Has anybody had any experience with one of these chucks? Any recommendations will be welcome.

    Thanks,

    Tim

  • #2
    Yeah working with a four jaw is a pain at first but if you need accuracy and gentle holding power that's the chuck you use.

    Three jaw chucks are delicate. One little wreck is all it takes to spring their jaws slightly and hamper their ability to hold work concentric and in parallel alignment with the spindle axis. Bust one parting tool in a three jaw and then inspect the accuracy of its grip. Bust a parting tool in an adjustable three jaw and you can correct for concentricity but the work may still stick out at an angle like a cow's ear. Concentric adjustment doesn't cure angularity.

    A four jaw is not rocket science but you have to practice with it. In a good shop an apprentice is not permitted to use any but a four jaw in his first rotation through the lathes. New guys absolutely positively HAVE to learn to efficiently use a four jaw chuck, not only as a rite of passage but because it's such a quick and effective work holder. Trust me, you will eventually come to think, "why the hell did I ever think a four jaw was a PITA?"

    Don't get me wrong. Three jaws chucks are irreplacible for some types of work. Three jaw chucks, four jaw chucks, collets, dead centers and driving dogs, face plates, spuds, pots, and so on are all but spindle tooling each with their advantages and range of purposes and a good lathe hands know which to use and when. Three jaw chucks are great for a noob's early experience but they are like training wheels. Sooner or later you will have to move on to other workholding systems to gain experience and efficiency. I use three jaw chucks often but I also use the four jaw. I'm changing chucks all the time. Sometimes I get lazy and use the three jaw when the four jaw is indicated but about half the time it's the other ways around.

    Here's something to shoot for: set up the four jaw and dial in a piece of cold roll to 0.001 in less than two minutes. I just went out to the shop and dialed in an old wrist pin to 0.0005" TIR taking 1:38 according to the stopwatch on my cell phone. I can still do it and I turned 68 acouple days ago. I was quicker back in the day but then I could leap tall buildings.
    Last edited by Forrest Addy; 08-06-2009, 02:13 PM.

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    • #3
      Tim:

      You might check the specs for your lathe chuck, but .003" is probably about what one would expect for TIR on your chuck. If you really need better than that you seem to have already provided a solution: use your 4 jaw. With practice the 4 jaw may even become your preferred chuck. But....hold it...I still use a 3 jaw chuck that probably doesn't do much better than yours. What does it really matter if you have .003" or .0005" of TIR on your chuck? It doesn't make that much difference unless you are re chucking something or you have to chuck something that have been previously turned and must be concentric. In which case the 4 jaw is what I use. Even .0005" is still out. Why settle for that?

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      • #4
        3 jaw chuck problems

        Thanks fellas,

        I agree that in most cases that a 4 jaw is the way to go when accuracy is desired. I will continue to work with the 4 jaw and I am sure that I will get better with it. Part of my problem may be that I am chucking old 1" schedule 40 rigid conduit. It is probably not very round to begin with and I think I might be squishing it. I will go today and get an old wrist pin to practice with. Still, it just bugs me to see the work wobble in the chuck (on the 3 jaw) and know that it is as good as it gets with this chuck. I was reading in "Machine Shop Trade Secrets" the other night. The author said something to the effect of: Don't bother messing with a crappy three jaw chuck, get a good one to begin with. Hence my quest for an adjustable 3 jaw.

        Tim

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        • #5
          I had read some where, maybe here, that you should check the accuracy of each of the three screws used to tighten the jaws. I know that my cheap Grizzly 3 jaw has it's most accurate screw. Give it a try.
          Mel
          _____________________________________________

          I would rather have tools that I never use, than not have a tool I need.
          Oregon Coast

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          • #6
            Lets see...

            Take a 3 jaw...

            Put 4 adjustment screws on it ala Adjust Tru..

            Tighten 3 jaw, adjust 4 screws... Will get you close for multiple same size work, but if it needs to be tighter than say .001, you still have to deal with adjustment screws.. And thats only if your workpiece is clean, round, and concentric..

            Manual 4 jaw is faster for manual tight tolerance work, why bother?

            Variable clamping pressure of a 4 jaw comes in handy, if you have a single thin area to clamp on...

            Collets are fast and accurate.

            Centers and Lathe Dogs work fine for work that can be supported that way..

            My three jaw gets mounted maybe 2 times a year. Sometimes I can live with .006 to .060 or so runout... on simple spacers and such, and working to more accuracy than needed, is just a waste of time....

            My 3 jaw is like new so it probably is still under .004 or so... Never do tight work with it, so have never measured runout with a ground wristpin...

            Comment


            • #7
              I've come to understand 3-jaw chucks are for production type work.
              1. Inhale oversized stock.
              2. Face/size/[drill]/[bore]/[ream]/[thread]/part
              3. GOTO 1

              If you need to re-chuck then 4-jaw, collets, centers-and-dogs, or faceplates are in order.

              My experience with tubing in 3-jaw chucks consists mostly of jumping, ducking, and going back in the house both more learned and muttering...

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              • #8
                My three jaw is out at least .003 I use paper under the jaws to rough center the material. I can get "really close" to center with that method. A couple of pieces of .003 paper will normally work.
                I use a 4 jaw to do repeat jobs.

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                • #9
                  4-jaws get easier/faster with practice. I find it helps to think of it almost as a pair of 2-jaw chucks, 90 degrees apart. Concentrate on getting the stock correct with respect to jaws 1-3 first, then get it correct with respect to 2-4. (Then go back and verify 1-3, of course, and make small adjustments). You'll need to leave 1-3 loose enough so you can still move the work as required with 2-4, and "loose enough" (but not too loose) is one of those things that comes with practice.
                  ----------
                  Try to make a living, not a killing. -- Utah Phillips
                  Don't believe everything you know. -- Bumper sticker
                  Everybody is ignorant, only on different subjects. -- Will Rogers
                  There are lots of people who mistake their imagination for their memory. - Josh Billings
                  Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                  Don't own anything you have to feed or paint. - Hood River Blackie

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                  • #10
                    A 3 jaw is fine..but if I have a choice and the part must be concentric to .001 or so, give me a 4 jaw anytime. Even with repeat work the same size it takes an amazingly small amount of time to re-indicate the new part. Just loosen the same 2 jaws and tighten the same two jaws in reverse sequence when you put the new part in to be turned (last loosened, first tightened). When you learn thru repetition the amount of force to put on the chuck wrench to center the part you will find the part is out only ten or so thousandths at worst...often much less.

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                    • #11
                      95% of my work is done with a 3 jaw because I turn most stuff from oversize stock. If I need to rework something I use a 4 jaw. There is no point in trying to get a three jaw extremely accurate, it won't stay that way.

                      The adjustable 3 jaws like the Buck chuck are a problem. They only have about .030" total travel of the adjustment. If someone has overtightened the adjustment screws you loose some of that travel. I have had to take them apart and machine the damage out. I usually machined in more adjustment travel and that helped.
                      It's only ink and paper

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                      • #12
                        There are lots of ways to get around the error found in most 3-jaw chucks if you need features to be concentric. The list includes:

                        Machining all of the critical features in one setup. Incorporating a chucking feature on the part which can be removed after all the other work is done can be helpful in some cases. Using a parting tool is also helpful.

                        Using spuds which are keyed so they always go into the chuck in the same position. The spud can also be used to check the ID/OD of the part, especially helpful for repetitive work.

                        Work-holding fixtures which are keyed so they always go into the chuck in the same position.

                        Turning the part 120 or 60 degrees in the chuck, and repeating the last pass without changing the position of the tool. Make two extra passes for 120 degrees or five extra passes for 60 degrees. This works best if there's a shoulder on the part.

                        I know some will may these are crutches or poor practice, but I've found they will give me the accuracy and concentricity I need for many of the parts I regularly make.

                        Roger
                        Any products mentioned in my posts have been endorsed by their manufacturer.

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                        • #13
                          Roger, a machinist has to use every trick he can find and I do the same as you do. I have found that if I keep rotating the part a little and checking the run out sometimes the part will indicate within .0005" to .001" when the best I was getting was .003". As the engineers would say it's FM.
                          It's only ink and paper

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                          • #14
                            Originally posted by tmc_31
                            Thanks fellas,

                            I was reading in "Machine Shop Trade Secrets" the other night. The author said something to the effect of: Don't bother messing with a crappy three jaw chuck, get a good one to begin with. Hence my quest for an adjustable 3 jaw.

                            Tim
                            James Harvey's book is very good. I have it and have used any number of his suggestions. However, Harvey is a professional machinist and for that reason makes the recommendation on using an "Adjust Tru" type of chuck twice in his book primarily for professionals. For most home shop machinists a regular 3 jaw chuck is perfectly OK. I know that there are any number of HSMs on this board that swear by the use of Adjust Tru type chucks, but given the cost compared to the price of your lathe it seems overkill given that a 4 jaw chuck will work just as well. If time is money the Adjust Tru makes a little more sense.

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                            • #15
                              Originally posted by Forrest Addy
                              Trust me, you will eventually come to think, "why the hell did I ever think a four jaw was a PITA?"
                              I'm pretty sure I said that last night.

                              I never had anyone teach me how to use a 4 jaw. In fact, i had never seen one until a few months ago when I bought my Colchester lathe. When I got the lathe up and running I fooled with the 4 jaw for a while and got frustrated, so I put the 3 jaw on and forgot about the 4 jaw. Well after grinding in the jaws on the 3 jaw I still couldn't get better than .004" runout on ground stock.

                              I watched this video yesterday. If the author is a member here, thanks for the video.
                              http://www.youtube.com/watch?v=2KMhx4DbyDg

                              It only took me a couple minutes using this guys method to get that same ground stock to less than .0005" runout. I think his method of finding the high and low spot then splitting the diff to zero the indicator is the key. I still did this with only one chuck key and it didn't take much time at all.

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