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Thread: dado saw blades

  1. #1
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    Post dado saw blades

    Recently purchased a CMT dado blade set to find it does not give me a flat bottom kurf as the 2 internal corers cut deeper so the cut has to be cleaned out by hand.Is this normal or do i have a faulty set . Appreciate any advice. Brit from brissie.

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  3. #2
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    Quote Originally Posted by brit View Post
    Recently purchased a CMT dado blade set to find it does not give me a flat bottom kurf as the 2 internal corers cut deeper so the cut has to be cleaned out by hand.Is this normal or do i have a faulty set . Appreciate any advice. Brit from brissie.
    Dado blades, either stacked dado sets, or the so called "wobble blade dados", tend to leave an uneven bottom to the dados or rebates that they cut. From a few magazine reviews of dado blades, I assume that it is a common trait with dado blades.

    My Freud dado stack leaves a cleanish trench most of the time, but in some instances the bottom of the trench can be uneven and/or "furry". In those instances, if the unevenness in the bottom of the trench prevents the joint from going together cleanly, or the end of the trench will be visible in the finished joint, then I clean up the trench with a hand router plane. A hand router plane is easy to set to the correct depth, takes only a few strokes to clean up the trench, and because of it's design it is imposible to cut the trench too deep.

    Regards,

    Roy
    Manufacturer of the Finest Quality Off-Cuts.

  4. #3
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    Quote Originally Posted by brit View Post
    Is this normal or do i have a faulty set .
    I don't think it's normal as my set, also a CMT set but admittedly bought quite a few years ago, cuts a perfect level trench.

    You say that two chippers are not correct but what about the others as in my set there are more then two chippers.

    Also a good saw sharpening place can fix it so that all cut the same depth.With a dado set if any blade needs sharpening then you should get the who set done in order to maintain a good cut.


    Peter.

  5. #4
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    I've got a dado set by infinitytools. I love it - it has chippers with 6 teeth and leaves a perfectly flat trench.

    Sounds like you have a problem with your set. I've also heard that wobble blades can leave an uneven finish too.

    Travis
    Some days we are the flies; some days we are the windscreen

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    Quote Originally Posted by Trav View Post
    I've got a dado set by infinitytools. I love it - it has chippers with 6 teeth and leaves a perfectly flat trench.

    Sounds like you have a problem with your set. I've also heard that wobble blades can leave an uneven finish too.

    Travis
    Wobble blades leave a rounded-bottom trench - deepest only in the middle. Nature of the beast.

    Joe
    Of course truth is stranger than fiction.
    Fiction has to make sense. - Mark Twain

  7. #6
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    ive got an 8 inch freud set, perfectly flat. user problem?
    Zed

  8. #7
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    Quote Originally Posted by Zed View Post
    ive got an 8 inch freud set, perfectly flat. user problem?
    Same here. My only addition to this is the outsides of the big blades cut down an extra 0.2mm to stop edge tear out. It is barely noticeable.

    It is a little furry, but I thought this was a deliberate so the glue had better bite.

    I talked about this with the local sharpener dude and he said it was trivial to fix if I wanted it smooth. Brit could do this, but maybe an email to CMT to seek their opinion?

  9. #8
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    A possibility is that some of the Dado blades/chippers are located on the thread of the Arbour and are not all aligned on the same axis, this will give an uneven bottom. This should be evident if you locate a blade and try to pull it up and down to see what clearance is there, or measure the Arbour and the blade to see what clearance you have.
    It's Ripping Time!!!

  10. #9
    rrich Guest

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    Uneven as in "Bat Ears" or a noticeable gouge through the trench?

    Bat ears would be at the walls of the trench and about .2 or .3 MM deep.

    A noticeable gouge attributed to the chippers being larger in diameter than the blades that cut the walls of the trench.

    The former is a fact of life and just the way that dado blades HAVE TO BE designed. Other than using a router bit there isn't a way around the problem. The latter is definitely a problem with the dado set.

    Assuming that you purchased the CMT set from either CMT or a responsible retailer, they should be more than willing to exchange the set with a new one at no cost to you.

    If you purchased the dado set in the secondary market or through a non-official retailer, re-sharpening may be the only option.

    There are router bits that are designed to clean out the dado trench. They are a flush trim bit with a 3 or 4 MM cutting edge and usually about a 9 or 10 MM diameter. The measurements are not terribly important. In theory, the dado is cut a MM or 2 less than intended. The router bit is used to cut the dado to the desired flat bottom depth and the bearing on the router bit rides on the walls of the dado cut on the table saw.

    BTW - The problem that I have is how are you blokes using dado blades? Aren't you constrained by "Euro Nanny Protect You From The World" safety standards? Aren't your table saws restricted in arbor length to prevent the use of dado blades?

    BTW2 - I still hate the metric system. I had to look up every measurement equivalent to make sense in metric.

  11. #10
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    Quote Originally Posted by rrich View Post

    BTW - The problem that I have is how are you blokes using dado blades? Aren't you constrained by "Euro Nanny Protect You From The World" safety standards? Aren't your table saws restricted in arbor length to prevent the use of dado blades?
    Gee, if you took away my dado capacity, I'd be devastated. I use my dado stack for lots of different things. You've got to be careful, like with any saw blade spinning at a zillion miles per second, but I can't see how a dado is that much more dangerous than a normal blade. Perhaps because you don't see the blade until it is coming out the back of the timber? The no-splitter thing is not an issue as you're not cutting through the wood.

    Trav
    Some days we are the flies; some days we are the windscreen

  12. #11
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    Quote Originally Posted by rrich View Post
    BTW2 - I still hate the metric system. I had to look up every measurement equivalent to make sense in metric.
    some "near enough for discussion" conversions ...
    3/8 = 10 mm
    1/8 = 3 mm
    1/32 = 1 mm
    1/64 = 1/2mm
    anything less, convert to sheets of paper

    the only two conversions that really, really matter are:
    12mm is not 1/2in -- router bits come in both sizes and a 12mm bit doesn't fit a 1/2in collet
    but 1/2in can be 13mm -- what's 0.3mm (or around 1/64) between friends -- router bits don't come with 13mm shanks

    and 6mm is not 1/4in for the same reason.

    and
    8mm is 8mm is never a conversion, because it's a standard size for size router bit shanks
    regards from Alberta, Canada

    ian

  13. #12
    rrich Guest

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    Ian, thank you. Your logical conversions are a big help.

    I've been burned by the 1/4 and 6mm thing. A retailer up here was selling 1/4 straight bits and delivering 6mm bits. (1/2 shank)

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