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Thread: Dados - Spiral Down Cut or Standard Straight Bit?

  1. #1
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    Dados - Spiral Down Cut or Standard Straight Bit?

    I need to buy a router bit to make dados in prefinished sheet goods. Normally I would get a standard two flute straight bit but am wondering if I should use a spiral down cut bit instead. It will be used in a Festool router running on the track. The bit diameter is 7/32", which may force me toward the spiral down bit. Which one would use?

  2. #2
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    In sheet goods I'd go with the spiral down. Less chance of chip out on the surface ply. IMHO
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  3. #3
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    A spiral upcut will draw the chips out of the dado - helps to clean it.
    Bill Arnold
    Citizen of Texas residing in Georgia.
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  4. #4
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    Quote Originally Posted by Bill Arnold View Post
    A spiral upcut will draw the chips out of the dado - helps to clean it.
    Will it not also pull up on the edges of the top ply and leave a rough edge, possibly chipping it?

    I use an upcut on mortices to remove waste where there is no worry about leaving a rough edge.
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  5. #5
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    Bill, I was thinking the same thing but Rennie does bring up a good point and he is using prefinished laminate material. So....
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
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  6. #6
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    It will be a shallow dado and I will take a couple of passes if I have to. If I was doing a mortise, I would go with the upcut. I thought that the consensus would have been for a downcut in this case and did not offer that up in my original choices. OK, I should have known better! Get any three woodworkers together and you will get three different answers. So is everyone leaning toward spiral bit (down or up in question) and not a normal straight bit?

  7. #7
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    spirel up and score it first.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  8. #8
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    Spiral down for dadoes and spiral up for mortises. Sharp in any case.

    Quarter inch deep dadoes are virtually self-clearing, so choose the downcut to get crisp edges on the thin (very!) veneer pf the the ply.

    Deeper mortises need all the help we can give then to clear out the swarf.

    Heat kills sharp edges. Clogged cuts generate heat.

    Hope that helps.

    RouterLady (retired)

  9. #9
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    Quote Originally Posted by Rennie Heuer View Post
    Will it not also pull up on the edges of the top ply and leave a rough edge, possibly chipping it?

    I use an upcut on mortices to remove waste where there is no worry about leaving a rough edge.
    That's a good point. I've used an upcut in my router table with good results on a variety of materials. I've used a downcut for edge trimming veneered panels for the reason you state. I can see where the downcut bit might make for cleaner edges on dados but I haven't had an issue - yet.

    Incidentally, for those who have to stop and think about the up and down terms (like me!) the direction is related to a handheld router. An upcut bit will pull waste down into a router table which can be confusing.
    Bill Arnold
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  10. #10
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    I say... upcut, toss the track, but use a shopbuilt underlay straightedge/zero clearance plate to prevent tearout & guarantee a match to your layout line. You know, the kinda' deal you make up from a stripe of Masonite with a hardwood straightedge attached to it, the kind you trim with the router & bit in question on the first use, and that is forevermore dedicated to that router & bit. You get real live zero clearance from one, and they do a VERY GOOD job of placing your cut exactly where you want it, AND holding down all the fibers around the cut in the bargain.

    A straight bit will pack up chopped fibers in the dado/groove something awful, and so will a downcut. I mean PACK.
    -- Tim --

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