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  1. #1
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    thicknesses of plywood and MDF

    Hi All,
    I know that plywood is slightly thinner than the nominal thickness by a 64th (or is it a 32nd?) and that you can get router bits for making dadoes to fit plywood thicknesses, but I was wondering if MDF is generally the same or if 3/4" MDF really is 3/4" thick.
    -John

    --------------------------

    "The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread." - Anatole France, 1894

    "I like a woman with a head on her shoulders. I hate necks." - Steve Martin

  2. #2
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    RE: thicknesses of plywood and MDF

    I find MDF to be spot on in thickness. Plywood on the other hand is undersized and the amount varies maker to maker, lot to lot, and sheet to sheet; varies enough that you can't rely on so called plywood router bits to give you a good fit.

  3. #3
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    RE: thicknesses of plywood and MDF

    I had previously found MDF to be precisely as marked but recently got some from HD marked as 1/4" that was actually 7/32" thick. Better to take a caliper with you and measure before buying.
    Measure once... cut twice.

  4. #4
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    RE: thicknesses of plywood and MDF

    Cool, thanks for the info, guys!

    --------------------------

    "The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread." - Anatole France, 1894

    "I like a woman with a head on her shoulders. I hate necks." - Steve Martin

  5. #5
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    RE: thicknesses of plywood and MDF

    Started thinking about this myself. Just wondering what you guys are doing for router bits, if thickness varies on sheet good like this. Are you guys buying a stack of bits to handle the various sizes or is there a trick? I use mostly 3/4" sheet goods and would like to get a bit for doing dados. Which should I buy? More then one I assume? Brands or even model numbers would be great.

    Sorry to hi-jack your question...

    Thanks,
    Doug


  6. #6
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    RE: thicknesses of plywood and MDF

    Dear Doug,

    I think some people *do* have a bunch of bits, but I can't afford that yet. So instead, I've been doing something like this:http://www.newwoodworker.com/rtrdadojig.html
    Except mine has two sides. I guess it's a little more like this one: http://www.shopnotes.com/main/sn76-toc.html
    Essentially, I took two nice straight pieces of hardwood, and routed a groove on each for the bushing. Now the half inch bit rides exactly at the edge, and I can do two passes, one out, one back, and if I've adjusted it correctly, I get a nice tight dado. At least, that's the theory... sometimes I push too hard in the middle... ;)

    Here's a better example, with good pics: http://www.woodmagazine.com/wood/sto...ml&catref=wd24

    Thanks,

    Bill

  7. #7
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    RE: thicknesses of plywood and MDF

    Excellent! That’s a great idea.

    I just had my first run in with a cheap router bit vs an expensive bit. I will never go back to cheap bits. I was getting a ton of tear-out and the bearing was in pretty bad shape (caused burn on the rub surface). I ran down to the local hardware store to get something that would do, but all they had was *freud* bits. I bit the bullet and paid $30 for a 3/8” round over bit. I was mad all the way home until I used it....changed my attitude in a hurry! It was a glass finish!

    Thanks for the link.

    Doug


  8. #8
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    RE: thicknesses of plywood and MDF

    occassionally the manufaturer will print the supposed thickness on the edge of the MDF. It is sometimes more accurate than what the price tag says it is at Home Depot (i.e. 1/2 vs. 15/32)

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