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Can runout and or shaft deflection cause kickback?

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  • Can runout and or shaft deflection cause kickback?

    I have been having some kickbacks as soon as my workpiece touches my spiral up cut trimming bit. The bit is brand new and my feed direction is correct on the router table. Interestingly, a 1/2" roundover doesn't kickback, but the finish is charred with lots of tearout.

    After exhausting all possibilities, I did a check and discovered very little runout on the shaft .005 outside and near 0 inside the collet. When I press firmly against the shaft, I cam get my indicator to move around .010" or more depending on how firmly I press against it.

    I am asking here because this is more of a machining question and not a woodworking question. Can shaft deflection cause a kickback? Is it normal to have any deflection? Does this worsen when spinning at 25,000?


    Sent from my iPad using Tapatalk

  • #2
    Maybe the bottom bearing in the router is past its best.

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    • #3
      Originally posted by old mart View Post
      Maybe the bottom bearing in the router is past its best.
      .010 from finger pressure makes me want to ask the same question.

      If it's flexing then the reading off the dial or other gauge you are using will act like the shaft is a spring. That is you push and the needle moves. As you alter your pressure the needle moves in response in a very linear and consistent manner. If it's bearing play then it'll sort of "click" to the new reading and stay there or move very inconsistently.

      Usually that sort of play will make the router sound like it's running in a very rough manner with quite a change in vibration as well. And often with a sort of new tooth itching howl instead of the usual clear sounding scream they make when new.
      Chilliwack BC, Canada

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      • #4
        Most routers have sloppy bearings bar the best ones, my old elu, hardly any, new dewalt about 5 thou, they are supposed to centre themselves I've been told but I'm not confident they do, I have a single flute 8 MM with a long shank, works great on the old elu, it's all over the shop in the dewalt.
        I know the elu is 30 y old but I'd buy another in a heartbeat, they are brilliant.
        I'm going to say a new set of bearings as suggested may alleviate the problem but is the bit bent also?
        Mark

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        • #5
          Originally posted by boslab View Post
          Most routers have sloppy bearings bar the best ones, my old elu, hardly any, new dewalt about 5 thou, they are supposed to centre themselves I've been told but I'm not confident they do, I have a single flute 8 MM with a long shank, works great on the old elu, it's all over the shop in the dewalt.
          I know the elu is 30 y old but I'd buy another in a heartbeat, they are brilliant.
          I'm going to say a new set of bearings as suggested may alleviate the problem but is the bit bent also?
          Mark
          All of the bits I tried were brand new.


          Sent from my iPad using Tapatalk

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          • #6
            Put a dowel pin in the collet and make the same tests/measurements.

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            • #7
              Originally posted by BCRider View Post
              .010 from finger pressure makes me want to ask the same question.

              Usually that sort of play will make the router sound like it's running in a very rough manner with quite a change in vibration as well. And often with a sort of new tooth itching howl instead of the usual clear sounding scream they make when new.
              Yeah, I'm leaning that way. I forgot to mention that I was getting enough vibration from the router to make a board dance off the router table. The router makes a gear like grind when it spins down. I ignored it thinking it's just how the PC 690 sounds. The Bosch 1617 is much quieter and more refined. I wonder if power tools, especially the routers and shop vacs, will eventually lose the loud universal motors for brushless.


              Sent from my iPad using Tapatalk

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              • #8
                Originally posted by RichardDepetris View Post
                Yeah, I'm leaning that way. I forgot to mention that I was getting enough vibration from the router to make a board dance off the router table. The router makes a gear like grind when it spins down. I ignored it thinking it's just how the PC 690 sounds. The Bosch 1617 is much quieter and more refined. I wonder if power tools, especially the routers and shop vacs, will eventually lose the loud universal motors for brushless.


                Sent from my iPad using Tapatalk
                It doesn't take a whole lot of bearing wear to produce that behavior. You might just be looking at replacing the bearings.
                Chilliwack BC, Canada

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