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Thread: Dadoing Plywood

  1. #1

    Dadoing Plywood

    My project is to make a 2'x4' mobile cabinet out of 3/4" plywood to store my tools and provide a work surface. First step is to take a 4'x8', using a edge guide use my Porter Cable 3 1/4 hp router to make dado cuts 4' long, on each edge and two slots inside where the inside panels will go. Once the slots are completed, I will cut it into two which results in two 2'x4'. Take another 4'x8', cut them 2'x4's minus 3/8" to compensate for the back panel of 3/8" plywood.
    Normally I'd make it out of oak plywood, but its too expensive.

    I have a proper size and underside straight bit set from Freud.

    A) What speed do I set my Porter Cable VS router for?
    B) Is it necessary to cut the edges with a utility knife and straight edge and mask tape to reduce tearout?

  2. #2
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    A 3/4" bit taking 1/8" passes I would run in the low to mid 20,000's. It is always worth the time to quickly score the line to prevent tearout; its too easy and quick a step to skip IMHO. I would be tempted to break my panels down before routing.
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  3. #3
    Also if I build this to be 2'x8', I had typo, I meant 2'x8' not 2'x4'.
    Assuming the casters are 3" and rated at 200 pounds each, do I really need 6 casters or can I get away with 4? I wouldn't want it to bow in the middle. It will have cabinet doors in the middle and drawers on both sides.

  4. #4
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    Hello,
    Assuming the casters are 3" and rated at 200 pounds each, do I really need 6 casters or can I get away with 4? I wouldn't want it to bow in the middle. It will have cabinet doors in the middle and drawers on both sides.
    I've moved away from using 3" casters to using 4" casters.
    The 4" just go over small pieces of debris a whole lot easier.
    Locking 4" casters is also a whole lot easier then locking 3" ones.

    To prevent bowing, add support into the base and/or build a sub base out of 2x4's.

    & no - 200# rated casters won't hold up on a cabinet of that size, even using 6 of them.

    Under a 4x8, you're in 900# plus territory.

    I made the mistake of using too light a caster under my "flip top" roll around cabinet that's only 1/4 that size and weighs just over 200# fully loaded.
    Trust me - retro fitting to replace the casters isn't a fun job...even on my smaller cabinet.

    The 200# rating is for load bearing capacity. It doesn't apply to or take into account the lateral forces of moving the load.

    I'm quoting here from Caster City (www (dot)castercity(dot)com):

    " You should never select on the basis of load capacity alone. Capacity ratings do not take into account the effort required to manually move a load. Capacity ratings are based on manual operation under ideal conditions. If these casters are going to be moved by mechanically powered equipment, consult us for a reduced capacity rating based on your application. If a human being has to move the weight, select the largest practical wheel diameter."
    Last edited by Rich Engelhardt; 06-21-2009 at 6:48 AM.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  5. #5
    Quote Originally Posted by Mike Wellner View Post
    A) What speed do I set my Porter Cable VS router for?
    That'll be a function of the cutter, the wood, the glue in the wood and your feed speed.
    There is no stock answer.

    B) Is it necessary to cut the edges with a utility knife and straight edge and mask tape to reduce tearout?
    It can help with chippy ply like OAK. I'd try it without on some scrap. Then see what extra exercises you gotta undertake to get it right.

    If you use a down shear cutter it'll almost eliminate all chip out.

  6. #6
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    For dadoes in plywood, I think the cleanest way is a good stacked dado set in a table or RA saw. Because of the grain orientation of plywood, you always get some tearout. If the dadoes are more for looks and alignment than for strength, I like to only dado down through the first ply or two instead of going halfway through the material. This is easier on the cutter and doesn't tear out as bad, and keeps the vertical strength of the sides of the carcase intact.

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