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3 Jaw Chuck Issues

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  • #31
    Brian, by the sound of it this will be your first time taking the chuck apart to clean it. If that's the case there's a pretty good chance that when it goes back together that it'll be just fine. But if it's still out you might try the trick I used to check the jaws for bell mouthing.

    I took a piece of larger size drill rod and just lightly pinched it in the jaws. But any consistent size shafting would work. I think I used my piece of 7/8" which is still around 2ft long. Then with an indicator on it I pushed it firmly away, released it and noted the reading. Then I pulled to me firmly, released it and noted the change. With the indicator about 6 or 7 inches out from the jaws I was getting something like .005 or .006" of non springing travel.

    I repeated this at a few rotational positions and it didn't get any better. Compounding this was my ability to poke a .003'ish shim between one jaw and the shaft when pulled for clearance. It wasn't much of a poke due to the rounding of the jaw's edge but it did fit at the nose of the jaws where back by the face of the body I couldn't even start it. Another indication of some bell mouth wear.

    If I tighten the chuck it holds fine without the ability to fit a shim. So it still makes good parts but clearly from what I can see I've got a few thou wear overall.


    As for how to grind it I've got a couple of options. One is a 1/4" size angle grinder I bought many years ago. Another is my old cheapie Foredom clone that has a handpiece diameter that would fit my larger size boring bar holder (currently the winning idea that I only discovered would work about 3 months ago but still need to "get a round tuit"). And yet another option that I've looked at for a while which I'd be able to use for a few things around here is one of the low cost CNC spindles like THIS ONE that is only $130C for the spindle, power supply, mounting bracket and collet set.


    Chilliwack BC, Canada

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    • #32
      Brian, how about a follow up? I could guess but would rather not.

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      • #33
        My lathe lay down and died on me just as I finished the last turned piece on the Trevithick engine. The lathe is at Concord where they will figure out why it quit and will adjust and possibly replace the spindle bearings and the spindle.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • #34
          Originally posted by brian Rupnow View Post
          My lathe lay down and died on me just as I finished the last turned piece on the Trevithick engine. The lathe is at Concord where they will figure out why it quit and will adjust and possibly replace the spindle bearings and the spindle.
          WOW, wonder if its the same failure you had just recently where you took it to Concord to repair. Lets hope its a simple inexpensive repair. You have had far too much practice loading that lathe up and transporting it lately.

          I am assuming when you say "lay down and died" you mean quit electrically, not some mechanical failure.

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          • #35
            Something electrical, but not the switch that was bad three months ago.
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

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            • #36
              Originally posted by brian Rupnow View Post
              Something electrical, but not the switch that was bad three months ago.
              Any word on your lathe?

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              • #37
                No, haven't heard a thing, but they were backed up a bit with other warranty work. I told them there was no rush--I had just finished the last turned piece for my newest engine when the lathe went funky. I expect I'll get a call this week. It made the guy laugh at the repair depot. He said that everybody came in and screamed at him and said there machine had broke down right in the middle of a project.--I was the only guy to ever bring a lathe in and say it had broke down at the end of a project and wasn't in a raging hurry.
                Brian Rupnow
                Design engineer
                Barrie, Ontario, Canada

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                • #38
                  Being nice to them will hopefully pay off, good luck, BR.

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                  • #39
                    Today I had a closer look at the run-out measurements on my headstock spindle. I must have been smoking rope when I measured the runout before. My previous measurements were taken with a dial type indicator, and I consistently got readings of 0.003" total indicated runout. Today I repeated the test with a lever style test indicator, and on three different registers it gave consistent readings of less than 0.001" total indicated runout. I'm feeling a lot better about the spindle now. I am about to tear down the 3 jaw chuck and clean it and check for irregularities--I have a feeling that it has gone bell mouthed, but I will see what it looks like when it is torn down..
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

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                    • #40
                      I always prefer to use a lever type indicator for this type of checking. The plunger type can stick sometimes when used horizontally as there is no assistance from gravity.

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                      • #41
                        I have completely disassembled the three jaw chuck. As expected, it was terribly dirty inside. I have washed all of the individual components in laquer thinners and blown them dry with compressed air. A close visual inspection shows no strange wear marks, burrs, or physical damage. If the jaws were bell mouthed, would that be visible? Should I use any grease when I reassemble this chuck, or just lightly oil the pieces as they go back together. I have the feeling that any kind of grease is going to attract chips and swarf like crazy.---Brian
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

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                        • #42
                          I like grease.

                          Bellmouthing is easily checked with it assembled. Chuck a round and straight object long enough to use the full length of the jaws. Then with a 1.5 thou feeler gauge. See how far back you can go. It shouldn't enter at all if the chuck is good.
                          21" Royersford Excelsior CamelBack Drillpress Restoration
                          1943 Sidney 16x54 Lathe Restoration

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                          • #43
                            Thank you for that Metal Butcher. I will try that as soon as I have the chuck reassembled. I'm waiting for suggestions right now relevant to whether I should grease any of the components before reassembly. I think lightly oiling the individual components might be preferable, as I think grease would just attract chips and swarf.----Brian
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

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                            • #44
                              I know that the chuck makers have their own brand grease, but I use motorcycle chain spray. This is not ideal as swarf does stick, but it would also stick to oil as well. Since it is easy to dismantle, there is no real excuse for not giving it a regular clean. Do you have both sets of hard jaws? Another way of checking bellmouthing is to turn a length of aluminium a little longer than the jaws and clamp the jaws onto the freshly turned part. Witness marks will tell you how much uneven contact there is.
                              Last edited by old mart; 11-21-2020, 04:41 PM.

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                              • #45
                                Yes, I have both sets of jaws.
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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