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Knurling's bad for bearings - Fact or Fiction?

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  • Knurling's bad for bearings - Fact or Fiction?

    I wish this were covered on Snopes.
    Is knurling with the old style "side-load" knurling tool REALLY as hard on bearings as people make it out to be?
    Has there ever been an actual instance where bearings have failed or gone bad due to side-load knurling?
    I ask, because it seems that on every knurling thread, or knurling tool sales add, or Ebay, or where-ever... everyone praises the almighty scissor-style knurling tool, and proclaims death & destruction to your lathe if you continue sinning and using the "Evil" side-load tool.
    So what's the poop?
    I can understand a lathe wearing out if it does nothing BUT knurling, all day, everyday, year after year.
    But the fear-mongering seems a bit much.
    Just sayin'

  • #2
    take a pass, get the electron microscope out and have a look

    Bearings eventually where out, whether you are drastically hastening that depends if you're doing a coarse knurl in prehardened 4140 in a single pass or mushy aluminum, if the lathe's a Pacemaker or asian mini.
    If you really load them and cause very minor brinelling, you've shortened their life, who knows if its very much and when/if you'll notice.

    Bottom line though is there's no really easy answer or way check. Given how fundamental they are to accuracy as well as difficult and expensive to replace, I think most guys, me included, sit in the better safe that sorry camp.....unless the lathe is rather heavy duty

    Also, be somewhat concerned about over straining the cross feed and nut
    .

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    • #3
      I think it has to depend on the lathe, the operator, the material, and how often it's done.
      As you said, in a production setting I could see it taking away from the life of the bearings, even that could be debatable, but at least seems reasonable on the surface.
      I think the bottom line would be the axiel?? (side load) thrust rating for the bearings and most lathes have a pretty substantional bearing rating. but I'm pretty sure that someone could exceed that if they got carried away. (what's gonna give first, the 1 inch stock your knurling, the knurler, or the bearings supporting the 2"+ od spindle?)

      edit: Or as Mcgyver said - "the cross feed and nut"
      Last edited by Scottike; 08-31-2011, 08:30 PM.
      I cut it twice, and it's still too short!
      Scott

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      • #4
        Time for a sage and worldly old fart response and a Sophoclean question: Nope. What fool told you that?
        Last edited by Forrest Addy; 09-01-2011, 12:08 AM.

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        • #5
          I was starting up some new industrial boilers for a company that was a sub-contractor to Lockheed, the boiler room was right next to one of the machine shops. They had bought a new big buck lathe, and this question came up, they had 3 stress engineers, with all kinds of test equipment for almost a week, running test on bump or side type knurler vs the scissor type. Their findings were it took exactly the same amount of side force on the spindle to raise the exact same size knurl, in the same type material, regardless of the type of knurler used.


          jack
          jack

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          • #6
            Depends on whether you have HSS or carbide bearings
            "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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            • #7
              I've found that the rubber bearings are are quiter and more forgiving
              I cut it twice, and it's still too short!
              Scott

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              • #8
                Best way to avoid wearing out your tools.... don't use them at all.

                Seriously. Tools are for using and making things. That's why we have them.

                No point in owning a lathe if you are afraid of it "wearing out" or some silly nonsense like that!!
                "The Administration does not support blowing up planets." --- Finally some SENSIBLE policy from the Gov!

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                • #9
                  Have you used one? If so you'd feel just how hard they are not just on the bearings, but pretty much the whole machine. To me it's a bit like owning a family sedan and always revving it to the redline, do it once and there shouldn't be a problem, but strain the engine like that constantly and that's when you'll start to see issues arrise.

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                  • #10
                    It doesn't have any effect on well lubricated plain (plane) bearings. Plane bearings are the heavy lifters of the bearing world.
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                    • #11
                      How ham fisted are you when you knurl? If you try to knurl in one pass your over doing it. Knurling SS or hard steel takes a lot of pressure. A small lathe may not take knurling so well. A 14"x40" gear headstock with good bearings can take the load.

                      What few times you will knurl will not hurt your lathe.
                      It's only ink and paper

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                      • #12
                        I don't see how a sissor knurl could come even close to the pressure required for a press knurl to work.

                        a sissor knurl asorbs all the 'side' force itself, all thats left is carriage feed force.
                        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                        • #13
                          Im not so worried about the bearings as much as I am about the crossfeed nut.

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                          • #14
                            Originally posted by wooleybooger
                            Im not so worried about the bearings as much as I am about the crossfeed nut.
                            That's my 2 cents worth too. It's not as much the spindle bearings but the rest of the machine that takes a hammering when knurling.

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                            • #15
                              Originally posted by Evan
                              It doesn't have any effect on well lubricated plain (plane) bearings. Plane bearings are the heavy lifters of the bearing world.
                              tis true plain shells are used on rolling mills [morgoil bearings] you cant get more extrime than a reversing roughing mill fitted with a couple of 11000A motors mangling slab steel!
                              i wouldent worry about your bearings as much as the cross feed as has been mentioned, it has affected mine as the backlash is getting worse, to the point i dont do much parting as a rule as the old dear is prone to snaching of late, a refit is on the cards! new harrison nut and screw wont be cheap so single pointing may be forced on me and my last effort on a square thread was abysmal!lol
                              regards
                              mark

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