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  • Lathe Chuck Balancing

    There was some discussion on here a while back about this topic, and so I thought I'd describe my process of using a static balancer and drilling to balance a lathe chuck.

    For a 4 jaw chuck:
    1. If you have a camlock spindle, find the happy spot where the chuck runs the truest and mark the chuck/spindle. Also, mark your chuck jaws if they aren't.
    2. Take a smooth, round, decent sized, and absolutely straight bar and dial it in as close to zero runout as possible. It needs to extend out the face and rear of the chuck by at least a few inches, so your spindle bore may be a limiting factor.
    3. Remove the chuck and bar from the spindle and place it on a static balancer. (Figure 1)
    4. Find the heavy and the light side and let the heavy side come to a rest at the bottom. Mark it and the light side. Now is the time to add a eyebolt hole on the heavy side if one desires.
    5. Start gluing on weights (washers, coins, whatever) to the lightest point at the radius that you intend to remove mass. Hot glue works excellent. Magnets are good too. (Figure 2)
    6. When the chuck is fully balanced, you can check it on the lathe to see if it is improved. Make sure that the added weights are inside if you do this and that they can't escape like and fire off like a bullet.
    7. Remove the weights and glue and weight it on a scale or balance.
    8. Using the density of cast iron, calculate the volume of material to be removed. Matweb.com is a good source for material densities. I converted inches to mm and did all my calculations with that, but you can convert to whatever unit you're most comfortable with. Grams and centimeters is probably easiest. Now is also the time to figure out how large of holes to drill, how deep, and how many. Depending on how much you need to take out, you may have to do multiple holes. (Figure 3)
    9. Fixture the chuck in such a way that you can drill the webs on the back side, while still leaving the straight rod in. It's important that the straight rod be left in for the entire process. (Figure 4)
    10. Drill your hole(s). Being conservative, I would go no more than 80% of the calculated value before checking. As it turned out for me, the math was very close and I could have gone right to 100%. (Figure 5)
    11. Check it on the balancer again. If necessary, keep removing metal until the chuck has no desire to rotate with any given angular position of the chuck. One can also check it on the lathe to ensure the balancing is making a difference.
    12. Make a final check on the lathe to ensure it's satisfactory, and you're done.
    There is many ways to skin a cat, and there are other, non destructive ways to balance chucks, like using glued in lead. Using this process I got a 12.5" Chinese 4 jaw that was shaking the whole lathe pretty bad to where it just has a whisker of shake at 750 RPM. If you don't have a static balance, you can still do this process by adding weights on the lathe using a guess and check strategy. It'll just take a lot longer.

    Click image for larger version  Name:	IMG_7546ECS.jpg Views:	13 Size:	115.6 KB ID:	1884510
    Figure 1: Sunstrand Static Balancer

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    Figure 2: Showing 6 washers glued in required for balance. Washers are glued at the same radius I intended to drill at.

    Click image for larger version  Name:	IMG_7581ECS.jpg Views:	13 Size:	200.7 KB ID:	1884513

    Figure 3: Calculations for the example chuck. In this case I had 42.1g of weight to remove. I used a 9/16" drill bit and needed to go 1 3/8" deep. I split that into two 11/16" holes. The math proved to be very close to correct.

    Click image for larger version  Name:	IMG_7580ECS.jpg Views:	13 Size:	229.8 KB ID:	1884511

    Figure 4: Setup Consists of 3 height matched risers, and then coupling nuts and long studs to use toe clamps on the chuck.

    Click image for larger version  Name:	IMG_7567ECS.jpg Views:	13 Size:	263.5 KB ID:	1884512

    Figure 5: Web was drilled as far away from the pin as possible.

    For those of you that prefer information in a video format like I do, I did that too. https://www.youtube.com/watch?v=-8ehuqRZebk
    Last edited by The Metal Butcher; 07-03-2020, 02:12 AM.
    21" Royersford Excelsior CamelBack Drillpress Restoration
    1943 Sidney 16x54 Lathe Restoration

  • #2
    I can see the point of this for a 3 or 6 jaw chuck, or a collet chuck which always hold symmetrical (round, hex) stock. With a 4 jaw, the majority of things that I hold seem to be massively imbalanced in the first place - boring a conrod end for instance - that I can't imagine that balancing the chuck would make much practical difference.

    If you use a 4 jaw for getting round stock exactly concentric, then yes, this would help.

    Ian
    All of the gear, no idea...

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    • #3
      Ian, he said the imbalance of the chuck alone was so bad it was shaking the entire lathe. I can see where you'd want to do something about that.

      TMB, does the distance from the axis of rotation not have to be considered when removing/adding weight? Or are you already doing that by virtue of putting the weights as near as possible to the same radius as the holes? (I'm kinda having trouble with my physics reasoning this morning.) Good presentation BTW.

      Never mind. The video cleared up my fog. Should'a watched that first.
      Last edited by lynnl; 07-03-2020, 06:59 AM.
      Lynn (Huntsville, AL)

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      • #4
        Hmmmmm. $1,000 for a static balancer. $80 for a precision rod. What did that cheap chuck cost now? I didn't see that in calculations.

        Comment


        • #5
          Interesting, it figures a four jaw with it's rough cast body would be out of balance. I don't ever recall or paid much attention to notice if any I have used over the years were balanced.
          I just need one more tool,just one!

          Comment


          • #6
            Originally posted by Ian B View Post
            I can see the point of this for a 3 or 6 jaw chuck, or a collet chuck which always hold symmetrical (round, hex) stock. With a 4 jaw, the majority of things that I hold seem to be massively imbalanced in the first place - boring a conrod end for instance - that I can't imagine that balancing the chuck would make much practical difference.

            If you use a 4 jaw for getting round stock exactly concentric, then yes, this would help.

            Ian
            I have to agree. Are 4 jaw chucks even balanced at the factory??? It would seem like an unnecessary added expense as far as production goes.

            JL................

            Comment


            • #7
              Originally posted by Ian B View Post
              I can see the point of this for a 3 or 6 jaw chuck, or a collet chuck which always hold symmetrical (round, hex) stock. With a 4 jaw, the majority of things that I hold seem to be massively imbalanced in the first place - boring a conrod end for instance - that I can't imagine that balancing the chuck would make much practical difference.

              If you use a 4 jaw for getting round stock exactly concentric, then yes, this would help.

              Ian
              Well, like you said it depends on what you do. We only have one 3 jaw in D1-6 pattern, an 8" 3 jaw. It doesn't run true enough for me to do second ops with it, and the grip strength really isn't that great. I don't do all that much square stuff, and I'd like to leave the chuck on for as long as possible (since they weigh like 100 lbs and I have no crane), so I may be using it to turn 1" steel rod and want to run run as fast as possible. I have yet to encounter any scroll chucks that aren't satisfactory.

              Originally posted by CCWKen View Post
              Hmmmmm. $1,000 for a static balancer. $80 for a precision rod. What did that cheap chuck cost now? I didn't see that in calculations.
              +$100k for a shop, +$1500 drill press, my this is getting expensive already!

              I mean I get what you're saying, but it's also not really fair. The static balancer wasn't bought for this. It cost next to nothing and looked like **** like everything else we get until we restored it. It's also balanced other stuff as well, and will continue to. For those who have surface grinders, have a wheel balancer is necessary anyway. The rod was just a boring bar blank I turned. Ideally it would have been a little bit better, I think it had some taper. An old hydraulic cylinder, or just some straight rod turned on the lathe is plenty good.

              Originally posted by JoeLee View Post
              I have to agree. Are 4 jaw chucks even balanced at the factory??? It would seem like an unnecessary added expense as far as production goes.

              JL................
              Well yes, but actually no. An 8" Buck 4 jaw was the first one I did a few years ago. It was arguably worse given it's size. It started shaking a little 10" Rockwell at 500 RPM. It had one small, factory drill peck on the back, and I added a bunch more. Now it's smooth up til 1500RPM. This Chinese one had one hole in it about an inch deep. So they had attempted to balance it, they just stopped when it got within their tolerance, which is pretty crap. I have another chuck to do soon, a Polish 12.5" 4 jaw, it's probably slightly worse than this one. I guess they felt it was an unnecessary expense as well.
              21" Royersford Excelsior CamelBack Drillpress Restoration
              1943 Sidney 16x54 Lathe Restoration

              Comment


              • #8
                I've never had the chance to buy a new chuck, but I'm sure the expensive makers balance them. Seems like you got a good deal if you don't mind putting a bit of elbow grease into it.

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                • #9
                  I just checked my 4 jaw. 12" Burnerd with a cast body. No signs of it having been balanced. I've had it up to 1,600rpm before now, no vibration when the jaws were equidistant from the centreline. The lathe will do 2,000rpm but that exceeds my pucker factor.

                  The casting still has the flashes from the moulding process. The only apparent concession to make things look pretty was to give the unmachined parts a nice coat of orange paint.

                  Either the casting was so well made that it didn't need balancing, or Burnerd didn't think it needed it, I don't know. Or maybe the lathe is massive enough to absorb whatever imbalance there is - it weighs 2 tons.

                  Ian
                  All of the gear, no idea...

                  Comment


                  • #10
                    Burnards are said to be a nice chuck. Our Sidney at 2.5 tons runs the 4 jaws OK at 800 RPM as it's heavy enough, but the Lagun at only 1.5 is too light. Neither of them would run at 1600 smoothly though​​​​​​. Sounds like yours is good to go!
                    21" Royersford Excelsior CamelBack Drillpress Restoration
                    1943 Sidney 16x54 Lathe Restoration

                    Comment


                    • #11
                      I have a Burnerd 5" 3-jaw that shows no sign of balancing, and yet its totally smooth all the way up to my lathe's max of 1200 RPM. The 6" 4-jaw was drilled full of holes on the backside to balance, it does OK if I do my part. But the 4-jaw is no-name, and its never been as smooth as the Burnerd.

                      If I ever get out of this hole and get rich enough, I'm gonna get Bison chucks. Or TMX (Toolmex).

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                      • #12
                        We have two independant four jaw chucks at the museum, a 6" lightweight Toolmex made from ductile iron with the jaws numbered and matched to the slots, and a cheap Chinese 160mm heavyweight which is nothing like the same quality. I mixed and matched the jaws in the cheapie to get the best fits and then numbered them and the slots. Both chucks have 6mm threaded holes in their fronts to hold balance weights. The weights will fit either chuck. The cheap one, being heavier duty, has bigger jaws and will be a candidate for having the jaws ground to ensure they are true. I am always on the lookout for a better heavyweight replacement, but the good ones are out of my price range.
                        The clamping of a nice bit of ground stock in the jaws with both ends sticking out is a very good method of balancing one of these chucks. So far, I have not noticed any particular vibration with these chucks. The Toolmex is made of billet stock SG iron with drilled lightening holes, so is unlikely to be unbalanced, either statically or dynamically.

                        Running a 12" chuck at 2000rpm is sailing close to the wind. Some of the Colchesters which would do that speed and more had special Pratt Bernerd chucks with either SG iron, or steel bodies.
                        Last edited by old mart; 07-03-2020, 12:35 PM.

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                        • #13
                          Originally posted by CCWKen View Post
                          Hmmmmm. $1,000 for a static balancer. $80 for a precision rod. What did that cheap chuck cost now? I didn't see that in calculations.
                          Yeah, 40+ years I've been doing this and I've never balanced a chuck, never seen it done, either. Buy a good chuck
                          and you don't need to worry about it...
                          Keith
                          __________________________
                          Just one project too many--that's what finally got him...

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                          • #14
                            Originally posted by LKeithR View Post

                            Yeah, 40+ years I've been doing this and I've never balanced a chuck, never seen it done, either. Buy a good chuck
                            and you don't need to worry about it...
                            Not ALL of us are made of money, and we're making the best of what we have.

                            Comment


                            • #15
                              Originally posted by LKeithR View Post

                              Yeah, 40+ years I've been doing this and I've never balanced a chuck, never seen it done, either. Buy a good chuck
                              and you don't need to worry about it...
                              Is an American made Buck not a good chuck?
                              21" Royersford Excelsior CamelBack Drillpress Restoration
                              1943 Sidney 16x54 Lathe Restoration

                              Comment

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