Blade Spin Down

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  • JoeyGee
    Veteran Member
    • Nov 2005
    • 1509
    • Sylvania, OH, USA.
    • BT3100-1

    Blade Spin Down

    It could be just me, but I have noticed lately that it takes my blade a really long time to spin down after I turn off the saw. Maybe it always has and I have just not noticed it. Do the BT3100's have any type of brake that is supposed to slow/stop the blade after turning off the saw? Am I just crazy?
    Joe
  • leehljp
    Just me
    • Dec 2002
    • 8429
    • Tunica, MS
    • BT3000/3100

    #2
    I never have timed it but it seems like 4 to 6 seconds for it to stop for me, once I cut it off.
    Hank Lee

    Experience is what you get when you don't get what you wanted!

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    • mpc
      Senior Member
      • Feb 2005
      • 979
      • Cypress, CA, USA.
      • BT3000 orig 13amp model

      #3
      My original style BT3000 takes probably around 5 or 6 seconds too. It does vary a little bit depending on which blade I have on it. A dado stack, or even the Freud box joint set (a 2 blade setup), has a lot more inertia than a plain blade and will coast for quite some time. I can feel differences in the weights of my "regular" blades so I'd expect some to take longer to spin up and spin down compared to the lighter ones. A regular kerf blade will probably take a bit longer to spin down compared to a thin-kerf blade for example. I've never paid close attention to it... but I wonder if a 80 tooth fine crosscut blade would have enough extra mass (extra and thus extra inertia) at the tips compared to say a 24 tooth rip blade? A little mass, at the outside edge of the blade, will cause a lot of inertia change since inertia is a function of both mass and distance. Actually, of distance squared.

      Have you done any lubrication or cleaning lately? Some fine dust can get caked onto the motor bearings adding friction... getting that crud cleaned out will make the motor+blade spin easier and thus take longer to spin-down. I suspect really worn motor brushes, or weak springs, could reduce motor friction a bit leading to a longer coasting time.

      BT3's don't have any sort of blade or motor brake mechanism. Some power tools are configured to short the motor's power leads together when the main switch is OFF. A spinning motor can be a generator... so having it feed a short-circuit (which is a very high load) will make it spin down quickly. It works great with DC motors and motors with permanent magnets; it's not as effective on A/C motors with field coils.

      mpc

      Comment

      • LCHIEN
        Internet Fact Checker
        • Dec 2002
        • 20914
        • Katy, TX, USA.
        • BT3000 vintage 1999

        #4
        BT3 does not have a blade brake.
        I had a 10" miter saw that had a blade brake, it would slow and stop very quickly - around 3 seconds I recall. Later in its life the blade brake contacts must have failed. As a result it would coast for 30 seconds or so before it came to a stop.
        Loring in Katy, TX USA
        If your only tool is a hammer, you tend to treat all problems as if they were nails.
        BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

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