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Correcting external jaw runout?

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  • Correcting external jaw runout?

    I got into the scrapbin to make a spider for the back side of my Grizzly lathe's bore, so broke out the external jaws to bore out some aluminum tube I had to fit over the end of it. I did make a nice press fit, and it's perfectly useable, but the bored section of the hole is something like 1/16" from concentric.

    I did break it down and clean it, and got a good bit of crud from inside, but that only accounts for most of the runout. It's still further than I would like.

    The 'internal' jaws really aren't bad, and thankfully they cover most of the work I do, but the external ones are mismatched or something. At least one actually appears to have been worked with the grinder slightly off center, or the other cutting operations were.

    I know the lathe is chinese and the chuck is certainly not the best part of that, but I'm looking for the inexpensive fix until I can pony up for a nicer chuck with two-piece jaws. Should I just try ordering another set of jaws and hope they fit the grooves they ride in well, or is there something I can do about it?

  • #2
    An inxpensive fix for one short jaw is a shim.

    Clamp and align a die grinder (tool post grinder if you have one!) to the carriage, open the jaws and pre-load somehow, spin the chuck slowly under power while moving the carriage in and out; grind to sparkout. Can't make it worse than it is...

    Oh.... clean up well...
    Last edited by lakeside53; 01-27-2012, 01:51 AM.

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    • #3
      I make have to make a holder for the Dremel, then. Or buy a toolpost grinder if I fine one cheap. I just hate shimming chucks. Don't trust it, despite knowing better.

      Is being out already going to affect the preload, or does it just need the tension?

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      • #4
        You only need tension.
        This may give you an idea of mounting the Dremel. I just welded a nut onto a piece of flat bar and clamp it in the tool post. I did at first have a hose clamp to go around the back of the dremel and around the flat bar, but found it wasn't needed.
        Dave

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        • #5
          1/16"?????

          sounds like you have one jaw one tooth out of alignment!

          Originally posted by Deus Machina
          I got into the scrapbin to make a spider for the back side of my Grizzly lathe's bore, so broke out the external jaws to bore out some aluminum tube I had to fit over the end of it. I did make a nice press fit, and it's perfectly useable, but the bored section of the hole is something like 1/16" from concentric.

          I did break it down and clean it, and got a good bit of crud from inside, but that only accounts for most of the runout. It's still further than I would like.

          The 'internal' jaws really aren't bad, and thankfully they cover most of the work I do, but the external ones are mismatched or something. At least one actually appears to have been worked with the grinder slightly off center, or the other cutting operations were.

          I know the lathe is chinese and the chuck is certainly not the best part of that, but I'm looking for the inexpensive fix until I can pony up for a nicer chuck with two-piece jaws. Should I just try ordering another set of jaws and hope they fit the grooves they ride in well, or is there something I can do about it?
          Tel

          Comment


          • #6
            Originally posted by Tel
            1/16"?????

            sounds like you have one jaw one tooth out of alignment!
            yeah... "mistiming", or else the jaws were actually in the wrong slots
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              On tooth alignment

              I have a Jet lathe that the nice person at the factory stamped 2 on jaw #3 and 3 on jaw #2 for the external jaws. The internal jaw set was stamped correctly. I would suggest checking that before any grinding.

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              • #8
                Originally posted by J Tiers
                yeah... "mistiming", or else the jaws were actually in the wrong slots
                The chuck on my Chinese mini lathe doesn't have marked slots. You just put the jaws in in the right order, but starting in any slot you like. I've tried all the combinations, but can't find any significant run out in any of them.
                Does this mean that the Chinese make more accurate chucks than say, Burnerd, where youy had to get the right jaw in the right slot?

                to answer the OP's query, my monies on jaws in the wrong order.

                richard

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                • #9
                  If you flip them over and line up the jaws, it's dead easy to see the offset progression. Get that right and compare to the numbers.

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                  • #10
                    Originally posted by Richard Wilson
                    The chuck on my Chinese mini lathe doesn't have marked slots. You just put the jaws in in the right order, but starting in any slot you like. I've tried all the combinations, but can't find any significant run out in any of them.
                    Does this mean that the Chinese make more accurate chucks than say, Burnerd, where youy had to get the right jaw in the right slot?

                    to answer the OP's query, my monies on jaws in the wrong order.

                    richard
                    Wrong slots is same-same with wrong order......

                    Mistiming is getting them in correct order, but a jaw is one space on the scroll from where it should be.
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      Actualy, it does matter what order you get the jaws in, and when you engage the scroll, In that if you get it wrong, it will be out some fraction (or multiple) of the scroll TPI.

                      Each of the 3 jaws has teeth on the bottom that are offset from the others, because the scroll is typicaly not triple start. Futhermore what order you let the scroll grab the teeth matter, Or you'll end up with an error equivilent to 1 pitch of the scroll.
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        I did check the order, first thing. It's easy to see, and brought to my attention how burred up the bottom of them are.

                        Matching these to their slot doesn't matter, as far as the runout goes. The scroll is what effects it. I do mark them, but that's only so I know which ones to put in instead of staring down at the scroll.

                        Also, no, the jaw itself is not 1/16" out--it was when it had chips in it. Now it's about ten thou. Putting them in any other order brings a very visible misalignment. For that matter, turning them so the outer sides of the other two are flush with the outer diameter of the chuck leave this one out enough to feel. Maybe 1/8 of a turn out.

                        I'm thinking it's mismatched.

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                        • #13
                          It sounds like you have been through every possibility so it's either live with it or fix it. I would fix it myself like you are thinking about.

                          Just to show you things like this happen allover the world, I bought a 250mm (10 inch) Fuerda 4 jaw. It sat in the box and was out of warranty when I went to use it. I got it out to find one jaw would not move when turning the chuck key, so after investigating I found the jaw was not contacting the screw as it was to short on the bottom by about 5mm. I removed the jaw and put it in my 200mm chuck and it worked perfectly, so they had mixed it up at the factory by putting a 200mm jaw in the 250mm chuck.
                          I thought it was strange because the jaw fitted the slots on both chucks perfectly, so the jaws must be ground to the same size (same set up) in both size chucks to keep costs down.

                          I contacted the place where I bought it and after explaining it and telling them I hadn't even used it, they changed it over for another one, but I checked it before leaving. LOL

                          Dave

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