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  • High speed spindle bearings

    I'm currently building a small desk top mill/engraver/(fill in the blank) machine and plan on using a 6" long ER16 chuck as the spindle. Since I plan on using this unit for (among other things) milling and drilling printed circuit boards, I want a spindle speed of at least 20,000 rpm to 25,000 rpm. ER16 chucks can be had fairly reasonably, but the bearings for that speed can be quite pricey.

    So, a few questions:

    What are the trade offs in shank diameter, say .5" vs .75"? Thicker would be more rigid, but there would be more mass to turn and the bearing are more expensive for the larger ID.

    For this speed, shank diameter, and tool size (no greater than .375"), is the annular ball type bearing the way to go or should I also look into tapered roller bearings? Considering the load, I'm thinking about using a single bearing at top and bottom, although a dual bearing at the bottom might be better.

    I guess the biggest question I have is for suggestions for bearing make and part number, with price an important part of the decision. I'm well aware that high speed bearings cost much more than the bearings for the motor on your 1500 rpm drill press. I'm just having problems paying $100 (and up!) each for bearing.

    So, for those of you that have made your own high speed spindles, what did you use that worked (and didn't work)? What are the design trade offs? Suggestion and comments greatly appreciated.

    Thanks,

    Tom

  • #2
    Don't know how much help this is but I googled "die grinder bearings" as those approximate the range you suggested and several hits got one of those exploded parts diagrams so the quickest route maybe to get a replacement bearing from some "easy" source like that and get something like a bearing series number then go for exact size you need...

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    • #3
      Hello,

      Have not used their product, but saw them at the CNC Workshops in Mich. this summer and would build around one of the spindles and vfd drives they sell.
      See CNC Zone for more tips.

      http://www.kelinginc.net/

      Brian
      Toolznthings

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      • #4
        +1 for the Keling spindles,why re-invent the wheel.
        I just need one more tool,just one!

        Comment


        • #5
          If you do want to build a spindle angular contact bearings would give you accuracy and should be good for the rpm. You'll need to spring load them against each other to eliminate clearances and you can use available wave or spring washers for the preload. Inner and outer races at one end (usually the load end) will be locked in place and either the inner or outer race of the bearing at the other end (usually outer) will be allowed to float to account for thermal expansion which can't be avoided. 1/2" spindle diameter should be sufficient. If you expected really heavy loads you can double up the bearings at that end but getting all the dimensions and bearings right so they actually share the load is probably more than double the trouble of a single bearing. There are existing designs for spindles like that and some can be found in the files section of the Quorn discussion group at http://groups.yahoo.com/group/quorn_owners/
          .
          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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          • #6
            Just about every grinder spindle I took apart for service had Fafnir bearings. Like 2mm or 3mm series. High speed precision bearings. You can look them up and get tech help from them also. Hope this helps.

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

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            • #7
              High Speed Bearings

              Routers, various Dremel(?) type hand tools, and many small high speed DC type motors run at similar speeds while some dental drills run at significantly higher speeds. You might investigate replacement bearings for these type tools. You might also investigate some of the better quality air powered die grinders since some of these run at extremely high speeds and also seem to hold up well. Of course your application may require higher precision than any of these provide.

              For extremely high speeds air or fluid bearings would seem to fill your requirements.

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              • #8
                Gentlemen:

                I've looked at the Keling and similar spindles and have been tempted. They solve most of the problems up front: no alignment or adjustment, collet ready to go, variable speed, and especially the ease of mounting (no machining except for a clamping block). The top end speed is fine, but what I failed to mention in my original post is the low end speed. I'd like to be able to run the spindle down to 1000 to 1500 rpm, if possible, to run bigger end mills. At 100 SFM and a .25" end mill, I need around 1500 rpm. This wide range of speed is why I've been considering a belt driven spindle (if I can find a belt that works at that speed). I may well be asking too much for the stiffness (or lack of stiffness) that the machine can provide.

                As far as using die grinder bearings, what is the normal runout (and end play)of this kind of bearing? The .010" range of PCB drills need -well- under .001" runout.

                I'll look carefully at the Quorn Yahoo group.

                Thanks for all comments.

                Tom

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                • #9
                  The quorn uses magneto bearings which are a cheaper angular contact bearing.

                  The keling spindle will go down to that low of an rpm but I dont expect to have any useful torque. It would be better if you got a true sensorless flux vector VFD to run it. But I kind of doubt you will be able to get anything useful at that RPM. You can run aluminum pretty fast.

                  Another thing is if you have a high speed spindle you can use small bits to take more smaller cuts faster and it will even things out a bit vs using a bigger end mill. And since you will be running carbide 100sfm is way low.

                  die grinder, dremel, and other bearings are all just generic bearings. Tiny PCB drills will snap if you sneeze. I have a spindle out of an excellon router and they are belt driven.

                  Another option over the cheap chinese spindle are the ones by Precise, now fischer-precise. They are very, very, nice. ABEC9 bearings standard. I picked up my 45000 RPM one for a couple hundred off ebay. I had tried the die-grinder/dremel/ BYO Toolpost grinder and the difference in finish was night and day. But you got to watch out with these spindles. Some of the older ones had a two phase motor and were driven by a separate motor-generator control. Also a lot of the newer ones are 3 phase but I dont know the specs. The one I have uses a brushed universal motor and has a variable reluctance shaft sensor to provide feedback for closed loop speed control.

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                  • #10
                    Building your own good spindle is not easy!
                    Do you have a cylindrical grinder? No? Forget it!
                    You can make one on the lathe, but the expensive bearings would be a waste of money, they won't last long.

                    Still wanting to make your own? Can you hold a few µm tolerance? A few µm runout (collet cone to bearing seat)? Harden and grind the inner spindle (with the collet)?
                    Intend to spend money for two spindle bearings, or three (two of them paired) or even 4 (all paired)?
                    The Quorn or Bonelle is a starting point for a spindle, but this construction is not suited for big axial loads, so no milling.

                    The belt is not the problem, my ID grinder spindle on the Myford runs with 40000 RPM with a flat belt. But the big wheel on the motor has 340 mm diameter. Makes 180 km/h belt speed.


                    Buy one, you won't make it better and cheaper.



                    Nick

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                    • #11
                      Originally posted by MuellerNick
                      Building your own good spindle is not easy!
                      Do you have a cylindrical grinder? No? Forget it!
                      You can make one on the lathe, but the expensive bearings would be a waste of money, they won't last long.
                      Why?



                      .
                      in Toronto Ontario - where are you?

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                      • #12
                        Why?
                        Because 20kRPM are too demanding with a wrong preload, oval bore, non-coaxial bearing seats, not considered thermal expansion, ...


                        Nick

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                        • #13
                          If you were to make a spindle on a lathe with no furthur finish grinding to the bearing surfaces you would, or should indicate the high point of ecentricity of each bearing surface so you would know how to orient the bearing according to markings of hi or low points. Spindle bearings are a VERY light press fit, finger preassure only, too tight of a fit will result in deformation of the presicion bearing and there goes your accuracy. I would think it is best to grind those surfaces so you have a smooth finish with little resistance to mounting the bearings.

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

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                          • #14
                            Originally posted by MuellerNick
                            Because 20kRPM are too demanding with a wrong preload, oval bore, non-coaxial bearing seats, not considered thermal expansion, ...


                            Nick
                            that doesn't explain why you say "Do you have a cylindrical grinder? No? Forget it!"

                            explain what there is about making a good 20k spindle that can't be done on a quality lathe between centres with a skilled operator. What tolerances do you insist are required?
                            in Toronto Ontario - where are you?

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                            • #15
                              that doesn't explain why you say "Do you have a cylindrical grinder? No? Forget it!"
                              It's the best answer you could get from asking a simple "Why?". Read posting #10, I explained it.


                              Nick

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