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Thread: Miter saw issue

  1. #1
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    Miter saw issue

    I've got a cheap Ryobi 10" Miter saw. (sorry don't have the model # here, but will look tonight). The saw starts, cuts, and runs smoothly, but it's recently started to squeal a bit as the brake kicks in. Yesterday the squeal went to a full yell during my last few cuts of flooring. So I got to looking at similar model diagrams of the saws on the ereplacement parts site. Not one of them shows a braking mechanism. Anyone know how the braking system works on one of these?

    I'm somewhat suspecting it has an electrical brake as part of the switch, but if so it must be self contained as the wiring diagram doesn't really show any extra wires. Doesn't quite explain the squeal and vibration it gives off either. I'll probably just go buy another saw, but if it's a $10 part and fix, I'll just keep it going as it has been cutting fine.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  2. #2
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    The brake is commonly electrical & controlled by the switch. When the switch is released, the polarity going to the motor is reversed for a split second or two, which causes the braking effect. The brushes are the first place I'd look.

    The switch normally has 2 circuits, one that's Normally Open, and the other Normally Closed...The NC circuit is used as the breaking mechanism. While your miter saw motor is spinning but without any power applied it is acting as an electric generating device. By shorting the output of this generating device (Which is why the need for the NC part of the switch.) you're creating a significant load on the generator. This is the breaking system on many devices with universal motors. The NC part of the switch almost always fails first due to very high peak but short duration current and voltage.

    Concerning the noise...I'd check to make sure a brush is not cracked/twisted/hung-up in the housing...could also be a bearing letting go...probably get a more informed response soon enough....
    The perception of perfection is perfectly clear to everyone else

  3. #3
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    Awesome, Thanks Ken, that's very informative and makes sense! Hopefully I'll have some time tonight to pull the brushes and check the switch.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  4. #4
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    Quote Originally Posted by Ken Cook View Post
    ...probably get a more informed response soon enough....
    I'm betting not. What you posted was a wealth of information already. (At least to me it was.)
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

  5. #5
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    Just as an example, here is what the saw sounds like when saw brake kicks in.


    Well I pulled the brushes out and neither had any damage, both were smooth and the edges were crisp. Next I opened up the switch cover and checked the switch using my ohm meter. It checked out ok as well. I suspect that there is some binding happening when the brake engages causing something in the drive to rub or bind the bearings. I didn't want to tear into the motor and since it starts up, runs, and cuts fine, also the fact the blade has a safety cover I opted to unplug the NC side of the switch (the brake wire).
    Click image for larger version. 

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    Here's what it sounds like when it's allowed to slow without the brake, which the spin down isn't much longer than with it.


    I'm still planning to get a new one, but should get some more use out of this one at least for chopping up scrap for the wood stove.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  6. #6
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    I'd still lean towards the switch going bad or dirty...if you wanna play with it some, reconnect the NC circuit then very rapidly pull & release the trigger a few times, this has worked for mine when making complaining noises, don't know if it's actually cleaning the switch or if it's simply allowing it to free itself, but has worked quite a few times over the years...another thought, though embarrassing, try removing &/or re-tightening the blade...DAMHIKT

    FWIW, having a dedicated firewood saw is living large
    The perception of perfection is perfectly clear to everyone else

  7. #7
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    Quote Originally Posted by Ken Cook View Post
    I'd still lean towards the switch going bad or dirty...if you wanna play with it some, reconnect the NC circuit then very rapidly pull & release the trigger a few times, this has worked for mine when making complaining noises, don't know if it's actually cleaning the switch or if it's simply allowing it to free itself, but has worked quite a few times over the years...another thought, though embarrassing, try removing &/or re-tightening the blade...DAMHIKT

    FWIW, having a dedicated firewood saw is living large
    I'll double check the blade tomorrow night and try that with the switch. It wasn't showing any resistance with the ohm meter, but never know...Thanks
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

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