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Miter saw blade coming loose

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  • Miter saw blade coming loose

    My DW 708 SCMS has had the blade loosen on me a couple times now. I replaced the blade recently and thought I tightened it up properly, but it somehow worked loose after a short time of using it. I tightened it up again and it worked for a while but loosened again.

    Thinking it was a bad blade, I put the old blade back on and everything seemed fine. Until today...when it loosened up again with the old blade.

    What the heck is going on with this saw? I have had it several years and have replaced the blade several times before with no problems. Any ideas?

    Thanks for your help.

    Doug

  • #2
    Re: Miter saw blade coming loose

    Does that model have a left handed thread? If not, start-up torque could loosen it.
    For no other solution I can think of, maybe make a sandpaper washer/shim and see if that keeps it tight.

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    • #3
      Re: Miter saw blade coming loose

      Do you have the original blade that came with this saw? If so, even if it is dull, put it back on and make a few cuts in some scrap pieces to see what happens. A lot of the "other manufacturer's" new blades are not as thick as some of the OEM blades, ask me how I know! We're talking maybe .010" (or less) here, one ten-thousandth of an inch in thickness, but enough that the blade will not tighten properly. IF you have a one-inch micrometer (as I do, and did) measure your original blade, then go to the store where you buy blades and compare thicknesses. On some saws the problem is not the bolt either, it's the little hub the blade fits onto, it's just slightly thicker than the blade and washer together. I've measured many in the stores and my friends saws. Even when you place the washer that comes with the saw on, the hub may, and can, stick out just a few thousandth's of an inch. This is what the bolt tightens up against on a lot of saws. Fortunately, being a retired machinist, I had the equipment to make a .010" shim for one of my friends saw to put behind the blade(s), and this fixed his. Hope this helps, David

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      • #4
        Re: Miter saw blade coming loose

        It is a left hand thread bolt, which is one reason I'm so confused by this...the bolt should never loosen up should it?

        I was really thinking that the blade thickness might be an issue, so I put an old blade back on - I have several old ones, but this one is a DeWalt blade, so maybe it was the original one...not positive. It seemed OK for a couple of days of very light use, but then it loosened up too. I have had this saw several years and use it almost daily. Never had this happen before, and I have changed the blade a couple of times over the years.

        There must be something I am missing, but I really believe all the parts are fine and correctly positioned. Is it possible for the blade brake to be causing this? That is the only thing I can think of. How can I check to see if it is the brake somehow causing this?

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        • #5
          Re: Miter saw blade coming loose

          The brake shouldn't/couldn't cause this, IMO, as the forces would be too slight to overcome a properly tightend blade. Frankly even if you spun the blade up to full RPM and then were able to immediately brake the motor... a one or two time incident shouldn't loosent the blade.

          I'm equally confused by what may be going on with this as it should NOT be any kind of occurance because of normal running/operating forces. I would normally look for a missing washer or similar component; or an arbor screw/nut that isn't being seated all the way.

          Does your DeWalt hav a threaded arbor that you are mounting the blade on and then tightening with a nut (as on a table or radial arm saw), or does it mount on a short spindle and is then fastened in position with a capscrew? (The latter is how my Ridgid CMS blade mounts, see attached image.)

          If it's the latter, is there any chance that the threads are damaged or that sawdust or other debris has found its way into the mounting hole and is keeping the screw from being secure. Also, make sure that the inner and out washers as well as the spindle is clean, free from dust, etc.

          Otherwise, you're looking at what I think is a rather dangerous problem and I'd get the saw into DeWalt service as soon as possible.

          I hope this helps,

          CWS
          Attached Files

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          • #6
            Re: Miter saw blade coming loose

            It looks very similar to your diagram CW. It has a hex head screw holding it onto the spindle, squeezing the blade between two "clamping" washers.

            I cleaned all the parts with acetone and a toothbrush and re-assembled. Made 3 or 4 cuts and it is still tight. Hopefully it will stay tightened up this time. I don't know what else to try. But you are right that it is a very uncomfortable thing to have happening.

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