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Lathe build underway: Part 1, the spindle

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  • #46
    Originally posted by J Tiers
    Originally posted by Lazlo
    The reason you pre-load the two angular contact bearings on a machine spindle is to reduce axial and radial runout. You can't do that with a double-row bearing.
    WRONG.

    The reason you preload ANY bearing is to reduce deflection under load.
    Jerry, you said this last time during the Bridgeport spindle bearing discussion, but you still don't get it.

    Preload, by definition, removes the internal clearance of a bearing by wedging the inner and outer races.

    Preloads
    http://www.rotoprecision.ca/Products..._Geometry.html

    Preloading is used to remove the internal clearance of a bearing and is achieved by applying a permanent thrust load in an axial direction. Preloading is used to eliminate radial and axial play, increase system rigidity, reduce run out, increase the assembly’s tolerance for vibration, and reduce operating noise.

    So Bridgeport, for example, used to take a pair of common 6207 radial ball bearings, grind the inner races, and preload-out the bearing runout. Bingo: Poor Man's angular contact bearing. Bridgeport did that on their Boss leadscrew bearings too.

    Similarly, the Monarch 10EE used ABEC-5 bearings that were custom preloaded to God-like precision. Not as good as Evan's South Bend though
    Last edited by lazlo; 01-02-2009, 03:45 PM.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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    • #47
      Originally posted by J Tiers
      Ball bearings DO NOT WEAR (if ball cages stay lubricated).

      A ball bearing that wears is contaminated with some crap that acts as a lapping compound.
      I'll have to tell that to the motor rewinders next time they order another 5,000 bearings as a job lot.

      "Hey George my mate on the internet says that bearing do not wear, A ball bearing that wears is contaminated with some crap that acts as a lapping compound."

      I can just hear the answer,
      "Well then, ask your mate where the crap comes from then when we fit factory sealed and greased bearings and running in a clean environment they are worn after a couple of years "

      Then ask him if he heard of Brinnell or is that a brand of dog food over there ?

      .
      Last edited by John Stevenson; 01-02-2009, 04:00 PM.
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



      Comment


      • #48
        Originally posted by John Stevenson
        I'll have to tell that to the motor rewinders next time they order another 5,000 bearings as a job lot.

        "Hey George my mate on the internet says that bearing do not wear, A ball bearing that wears is contaminated with some crap that acts as a lapping compound."

        .
        If the ball bearings are perfectly spherical and the races are perfectly smooth, then there's only the rolling action which means that it should in theory never wear. However, no surfaces are perfectly flat or round and is limited by the manufacturing process and ultimately the size of the steel grain itself. Think of it as n-th sided polygon rolling in n-th sided polygon.

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        • #49
          John,

          Would you like to see a video of the measurement process? It appears you don't wish to take my word for it. Careful what you ask for though.
          Free software for calculating bolt circles and similar: Click Here

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          • #50
            Not exactly that many of us who take on a custom lathe build!

            A lot of guys have built the smaller machines, myself included. But a 16" swing lathe for metal? That's a pretty big undertaking!
            This nice thing is we have so much info available. And much of what were very complex mechanical gearing and devices needed on a good lathe for the feeds and threads, can now be done easily and simply with cnc. This greatly simplifies building a usable lathe in the shop.
            Hey, if the bearing setup works, then great. If not, then Evan can switch to plan B and all he is out is some time and maybe some material.
            I would give it a try.
            Looking forward to see the headstock and lathe bed!

            Steve

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            • #51
              Not as good as Evan's South Bend though
              It uses plane bearings and the spindle is hardened and precision ground. Why should it have significant runout? As long as it is round the measured runout should be very close to zero. That is what is being measured in the baseline case, the roundness of the spindle.

              Rolling element bearings will never be as good as hydrodynamic plane bearings.
              Last edited by Evan; 01-02-2009, 04:56 PM.
              Free software for calculating bolt circles and similar: Click Here

              Comment


              • #52
                According to the South Bend catalog, a SB "toolroom" lathe had a runout spec of .0003", and a SB "engine lathe" (everything else not classified as a toolroom lathe) has a runout spec of .0005".

                This is measured on a 12" test bar.
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                Comment


                • #53
                  That's nice. I don't really know where the +- 3 micron runout comes from. I am assuming it is the spindle as I tried for quite a while to reduce it and couldn't. It's what I measured and I measured it accurately. If you don't like it or believe it then suit yourself. Unless you can demonstrate an error in my method though you cannot show that my measurements are incorrect.
                  Free software for calculating bolt circles and similar: Click Here

                  Comment


                  • #54
                    Not sure what South Bend meant by those specs. My SB9 which has my own bronze bearings has much less than .0003" run out.
                    The run out is going to be determined by 2 important things with a plane bearing.
                    One, how round is the spindle.
                    Two, how consistent is the oil film between spindle and bearing.

                    Without oil there is up to .001+" free clearance between spindle and bearing surface.
                    Once the oil film is established then run out should be about as good as the spindle was ground unless something is very wrong.
                    .0005" is ridiculous.
                    Even a mini lathe spindle with cheap deep grooves is only around .0003".

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                    • #55
                      What is being measured ? if you are measuring round on or close to the bearing then it should be as close to 0.000000000 [ approx ] as possible.

                      If you are measuring a test bar fitted into the spindle taper both at the chuck end and 12" out then two variables come into play.
                      [1] the relationship between the taper eccentricity compared to the bearing diameter and
                      [2] the alignment along the spindle centre line of the taper.

                      [1] will give you run-out and [2] Will give you extended run-out.

                      Most test spec sheets, like Schlesinger's work on the test bar fitted to the taper.

                      .
                      .

                      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                      Comment


                      • #56
                        John, I see. That measurement takes into account several variables.

                        I can see this measurement being important for collet use for example.

                        It's not a runout measurement that is very valid for this discussion right now IMO.

                        Steve

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                        • #57
                          "If the ball bearings are perfectly spherical and the races are perfectly smooth, then there's only the rolling action which means that it should in theory never wear."

                          Because of the varying surface speed of the balls at different distances from the center, there will be scrubbing between the balls and the races.

                          I can't think of anything except a needle bearing that is purely rolling.

                          Comment


                          • #58
                            Originally posted by S_J_H
                            Not sure what South Bend meant by those specs. My SB9 which has my own bronze bearings has much less than .0003" run out.

                            Even a mini lathe spindle with cheap deep grooves is only around .0003"
                            Steve, a mini-lathe isn't anywhere close to 3 tenths runout! How are you measuring these values?

                            My mini-lathe has about a thou of runout, which is pretty typical. Here's a copy of Gagetbuilder's Sieg 7x10 test report, which shows a measured runout of 8 tenths, and an allowable runout spec of 1.6 thou. That's not surprising, since a common (non-precision) radial ball bearing has a max runout of 3 thou:

                            Last edited by lazlo; 01-02-2009, 06:49 PM.
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                            Comment


                            • #59
                              And for some perspective, the Deckel toolroom mills have a runout spec of 4 tenths:

                              [/QUOTE]
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                              Comment


                              • #60
                                What a crummy bearing for that application. Best would be to get rid of it now- my address is---

                                Looking at the drawing, it would seem that the inner race is pretty thin at its center. You could have ground through that to separate the inner race into two pieces, then you'd be able to set the preload yourself. ( I take a bow, and offer to show my credentials as a HSBE- home shop bearing engineer)
                                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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