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  • #61
    The quality of Chinese made bearings is a lottery. When we got the drill mill as a basket case which had been left under a tapaulin in somebodys garden for 3 years, I had to replace the lower spindle bearing. I would have had to wait three weeks for a branded one, so took a chance on a Chinese one and it has been going for 5 years. I am thinking of replacing the grease soon and will take a long hard look at both bearings then. I would certainly buy SKF or equivalent if needed, they are not that expensive.

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    • #62
      Originally posted by dian View Post

      oh, and why roller bearings? very simple: it is much easier to make a precise cylinder than a precise sphere. (not that this really matters for most practical purposes.)
      I don't see anything easy when we move to tapered roller bearings. Price and availability also reflect this: P4 angular contact bearings or deep groove ball bearings are dime in a dozen whereas P4 tapered roller bearings are mostly custom order big bucks.

      Location: Helsinki, Finland, Europe

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      • #63
        Originally posted by dian View Post

        your thoughts are interesting, but im afraid the bearing manufacturers have gone through these considerations for us in this case.

        1. timken also makes through hardened bearings (as skf probaly makes case hardened ones).
        2. through hardened bearings are perfectly suitable for most applications. why not laser harden of ceramic coat them? we are not talking aero-engines here.
        3. the typical 52100 will not through harden more than 5 mm (10 mm diameter) anyway, with conventioal heat treat that is.
        4. the exact structure of the steel (e.g. bainitic/martensitic, % retained austenite etc.) will have more influence on properties than through/case hardening. the case often winds up bainitic.
        5. nitriding, carburising, nitrocarburising, plasma etc. are not only expensive but require additional alloying to work (e.g. vanadium for carburizing)
        6. contact stress in bearings can easily go deeper than the case destroying the steel blow the surface. usually 60 hrc is deemed sufficien, atainable without fancy processing.
        7. on the other hand some plasticity aids the surface to endure deformation by debris without micro-cracking, hence the advantage of a bainitic structure than is amenable to deformation.

        oh, and why roller bearings? very simple: it is much easier to make a precise cylinder than a precise sphere. (not that this really matters for most practical purposes.)
        I’ve had the bearing companies do the tests and ran the tests myself to verify. Saw no difference. Yet the through hardened (yes through) failed in service and the case carburized did not. Failures were due to spalling initiating at the surface from brindle spots on the roller and cone surfaces. Added some debris to the lab test oil and confirmed the difference. So as I had said, if debris is a possibility look to case hardened not through hardened. Mfg doesn’t matter.

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        • #64
          Originally posted by Bented View Post
          100% inspection works well if you can sustain manufacturing $1000.00 components and sell them for $500.00 (-:

          I am pulling the legs of the "Made in Asia = Bad crowd".

          I am posting this employing a Dell Computer©, Logitech™ mouse and keyboard and a Comcast™ WIFI router.

          I do not currently own any Apple products.
          Got it!

          Electronics are one of the better-controlled product types, and of course Dell etc buy enough to have very good access and control of the process, as well as having found and/or developed good "partner manufacturers".
          CNC machines only go through the motions

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          • #65
            Originally posted by dian View Post
            ...........

            oh, and why roller bearings? very simple: it is much easier to make a precise cylinder than a precise sphere. (not that this really matters for most practical purposes.)
            The technology to make very precise spheres in bulk quantity has existed for over 120 years now. I have an old reprint of an article from around 1900 which explains it, and the same basic process/methods are still used now.

            If anything, the sphere has fewer variables than a roller. I do not think making spheres is any problem now.
            CNC machines only go through the motions

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            • #66
              Originally posted by dian View Post

              " bolted my lathe to a granite surface plate"

              great. thats the way to do it. biggest cost to result ratio.
              Not sure what you mean by that. The plate cost me $100, and iunno about you but i feel that $100 is a pretty bloody cheap price for massively increasing the capabilities of a machine. I certainly got more that $100 worth of results out of it

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              • #67
                epic: i ment what i said, was not being ironical. my small lathe is on a 6" epoxy-granite slab. people generally dont believe what difference a solid foundation makes.

                j.t.: i talked to a timken engineer (tobias storz) this week and thats what he mentioned. (you are referring to the idea that its easyier tomake a very precise cylinder that a very precise spere, right?)

                rick: there is plenty of evidence to the contrary. case hardened bearings are not a generally better solution. it depends on the application, alloy etc. and is complicated (as everything else in metallurgy). sorry, but to make such a recommendaton is like telling somebody to buy a car with a v-6 because it going to be faster than a 4-banger.

                edit: a carburized case can end up having tensile stress of up to 200mpa at the surface (while having compressive stress below), obviously leading to problems.
                Last edited by dian; 03-14-2021, 06:26 AM.

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                • #68
                  Originally posted by dian View Post
                  ........

                  j.t.: i talked to a timken engineer (tobias storz) this week and thats what he mentioned. (you are referring to the idea that its easyier tomake a very precise cylinder that a very precise spere, right?)

                  ......................
                  I said that the method of making spheres is very old and well-known, well-developed, such that they can be, and are, made in huge quantities to any desired precision. The making is not a big problem.

                  Spheres have one critical dimension, diameter. Rollers have two, diameter and cylindricity (or cone angle). Both share the "perfection of roundness" requirement, so that is the same issue either way.

                  Spheres are not made by elves filing and polishing them individually until they are round. They are made in what amounts to a statistical method of grinding them in large volume, and have been since the late 1800s.
                  CNC machines only go through the motions

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                  • #69
                    Originally posted by dian View Post
                    there is plenty of evidence to the contrary. case hardened bearings are not a generally better solution. it depends on the application, alloy etc. and is complicated (as everything else in metallurgy)

                    edit: a carburized case can end up having tensile stress of up to 200mpa at the surface (while having compressive stress below), obviously leading to problems.
                    (One) reason for Timken to use carburizing was that North American ore/steel wasn't enough pure for bearings. Lowering the carbon content helped to get rid of other impurities(or vice versa) and they were able to get to low inclusion level needed for bearing steel.

                    Swedish steel and especially the mines SKF used was superior compared to US domestic steels 100 years ago.
                    Location: Helsinki, Finland, Europe

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                    • #70
                      Originally posted by MattiJ View Post

                      (One) reason for Timken to use carburizing was that North American ore/steel wasn't enough pure for bearings. Lowering the carbon content helped to get rid of other impurities(or vice versa) and they were able to get to low inclusion level needed for bearing steel.

                      Swedish steel and especially the mines SKF used was superior compared to US domestic steels 100 years ago.
                      Yes, this is quite true. At the time, most steel makers in North America were using coal in their process, this added a lot of impurities. The American ore quality was actually quite high. The books which I have from that time, say that the Swedes steel is the best for tool making because they used wood charcoal -- a much purer and cleaner product.

                      After about 1920, Bethlehem Steel switched entirely to the Siemens-Martin process in basic open hearth furnaces to burn out the impurities, and would later add carbon as needed. The really high quality stuff was remelted with an arc in a vacuum, for bearings. Using cheap hydro power from Niagara Falls.

                      At their peak in the 1950's Bethlehem was operating 2 dozen furnaces with a capacity of 60 tons each, per 8-hour shift. Today there is nothing but a large park with some wind turbines standing there. And lots of unemployment. I know all this because I live there, and have their original books from the old times.
                      Last edited by nickel-city-fab; 03-14-2021, 01:59 PM.
                      25 miles north of Buffalo NY, USA

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                      • #71
                        Originally posted by nickel-city-fab View Post

                        Yes, this is quite true. At the time, most steel makers in North America were using coal in their process, this added a lot of impurities. The American ore quality was actually quite high. The books which I have from that time, say that the Swedes steel is the best for tool making because they used wood charcoal -- a much purer and cleaner product.............
                        Surely you mean "coke", coal that has been cooked so that the volatile impurities (volatile at high temperature) have been driven off, leaving nearly pure carbon. Very similar to charcoal, might not be "quite" as pure. Source is a set of books on the entire steelmaking process from the late 1800s, so the use of coke is very longstanding, well over 100 years.

                        A lot of impurities are driven off at yellow heat.....
                        CNC machines only go through the motions

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                        • #72
                          Originally posted by J Tiers View Post

                          Surely you mean "coke", coal that has been cooked so that the volatile impurities (volatile at high temperature) have been driven off, leaving nearly pure carbon. Very similar to charcoal, might not be "quite" as pure. Source is a set of books on the entire steelmaking process from the late 1800s, so the use of coke is very longstanding, well over 100 years.

                          A lot of impurities are driven off at yellow heat.....
                          Yes, coke. My bad. At the time Bethlehem designed their plant with the assumption that the coal would be high quality. When it came out of the coke ovens, it turned out to be not so high quality, this messed up their process until about 1930. They were using the gasses from the ovens to power giant engines that ran the blast furnace blowers, but the gas quality was very poor and they had to abandon that setup. They continued to use it in gas producers that actually fired the open hearths. Said coke was used in the blast furnaces in the usual manner. To create the pig iron.
                          Last edited by nickel-city-fab; 03-14-2021, 02:13 PM.
                          25 miles north of Buffalo NY, USA

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                          • #73
                            Originally posted by MattiJ View Post

                            (One) reason for Timken to use carburizing was that North American ore/steel wasn't enough pure for bearings. Lowering the carbon content helped to get rid of other impurities(or vice versa) and they were able to get to low inclusion level needed for bearing steel.

                            Swedish steel and especially the mines SKF used was superior compared to US domestic steels 100 years ago.
                            interesting. now i see where the expression "schwedische gardinen" (sweedisch curtains) for iron bars in jail comes from.

                            edit: on second thought, can you explain the impurities agrument? it seems improbable they would use steel without secondary processing. it makes a difference if your building the golden gate bridge or want to make bearings. i assume we are talking phosphorus here. to remove it calcium and oxigen is used in the ladle.
                            Last edited by dian; 03-17-2021, 07:03 AM.

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                            • #74
                              Originally posted by nickel-city-fab View Post

                              Yes, this is quite true. At the time, most steel makers in North America were using coal in their process, this added a lot of impurities. The American ore quality was actually quite high. The books which I have from that time, say that the Swedes steel is the best for tool making because they used wood charcoal -- a much purer and cleaner product.

                              After about 1920, Bethlehem Steel switched entirely to the Siemens-Martin process in basic open hearth furnaces to burn out the impurities, and would later add carbon as needed. The really high quality stuff was remelted with an arc in a vacuum, for bearings. Using cheap hydro power from Niagara Falls.

                              At their peak in the 1950's Bethlehem was operating 2 dozen furnaces with a capacity of 60 tons each, per 8-hour shift. Today there is nothing but a large park with some wind turbines standing there. And lots of unemployment. I know all this because I live there, and have their original books from the old times.
                              I can't remember/find the details at the moment but IIRC Swedish ore was better suited for high quality steel production even after moving away from wood charcoal.
                              (Other steel makers catch up in the quality when they started using mentioned vacuum arc remelt steel.)

                              By the time of WW2 US was pretty much self-reliant on high quality bearings (worlds largest ball bearing manufacturing plant at that time was SKF Pennsylvania)

                              But both Britain and Germany were still heavily reliant on Swedish SKF bearings:
                              https://www.econhist.gu.se/digitalAs...645_golson.pdf
                              https://en.wikipedia.org/wiki/Ball-bearing_Run

                              "A July 1943 memo demonstrates how slowly the British bearings industry adapted to producing Swedish‐quality bearings. While virtually all Swedish‐imported bearings went to designated priority aviation and tank uses, by July 1943 only 34% of British production was suitable for aircraft engines and similar applications. The quality was expected after a year to improve by 3%, making 37% of British bearings aircraft‐worthy by June 1944 that 41% would be aircraft‐worthy by December 1944.80 By contrast 100% of Swedish imported bearings were aircraft worthy. Swedish machinery was used to obtain these UK production rates. Without the Swedish machinery, successful production rates would probably have been even lower, suggesting that a long‐term process was needed to build a suitable replacement ball bearings industry in Britain"
                              Location: Helsinki, Finland, Europe

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                              • #75
                                "SKF controlled the requisite high‐strength raw materials, machine tools, intellectual property and patents necessary":

                                i suspect it was rather the latter that the first.
                                Last edited by dian; 05-11-2021, 10:17 AM.

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