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Thread: Making grooves for 1/4" plywood

  1. #1
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    Making grooves for 1/4" plywood

    I'm making something with frame and panel construction and the panels will be 1/4" maple plywood. I am now on a hunt for a slot cutter to make grooves for the plywood panels. I've tried a 7/32 cutter which is slightly too big and a 3/16 cutter which is slightly too small. I may use the 7/32 cutter and pin the panels so that they don't rattle but I wondered if anyone had a line on a cutter that would be the correct size with no additional "jigging" to make it work.

    Rockler makes a router bit for plywood sizing but I find it easier to use a slot cutter.

  2. #2
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    Run it twice with the 3/16 cutter, adjusting it for correct fit for the second run. This gets you the result without costing you another cutter. Cheers

  3. #3
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    Wayne's advice is good. You can also buy adjustable slot cutters (from Freud and others) to get the exact slot width you want in one pass.

  4. #4
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    Check out the Freud 99-036 Adjustable tongue and groove set. It is adjustable at .002 inch increments for stock thickness of ½” to 1-1/4” and groove widths of 7/32” to 3/8”.
    99-036.jpg
    Lee Schierer
    USNA '71
    Go Navy!

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute

  5. #5
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    I bought "plywood" router bits. What a waste of money, since no one makes it identical, and it keeps getting thinner. How I do it is get it close (on the slot side) and shave the back-side of the panel with a router table, and make it a glove fit. Since Ply will not expand, its never an issue.

    Works like a charm, and none of this fiddling with dado stacks etc. I've got a nice set of Forrest dado with magnetic shims, that I've not used in years.

  6. #6
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    The ply may be 5.5 mm and even that will vary a little. When I was faced with oversized slots, I put masking tape on either side of the slot for a few inches either side of center then put a little silicone caulk in the groove, not too much so it doesn't squeeze out. That holds the panel but there is some flex. Never had a finishing problem and no rattle.

  7. #7
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    Thanks for all the great suggestions. My first choice would be the adjustable cutters but they seem a little pricey for a one time project. I'm very lazy and I'm trying to avoid a lot of fussing around with this. I will probably try Curt's suggestion of masking tape and a little silicone caulk on a sample. If the tape and caulk seems problematic I will use the 3/16 cutter and making a second pass for a "perfect" fit.

  8. #8
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    If you proceed with caulk, avoid anything containing silicone. It will be a polishing/painting disaster. Use a water based gap filling caulk or a polyurethane chalk, both of which are compatible with finishes. Cheers

  9. #9
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    Quote Originally Posted by Curt Harms View Post
    The ply may be 5.5 mm and even that will vary a little.
    Bingo...most plywood these days is metric, but still has some variability as you note.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #10
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    Quote Originally Posted by Wayne Lomman View Post
    If you proceed with caulk, avoid anything containing silicone. It will be a polishing/painting disaster.
    <snip>
    GE may beg to differ

    http://www.caulkyourhome.com/ge-sili...e-silicone.php

    though it appears to be a blend. I don't know that polyurethane caulks were around when I was doing those panels. Does polyurethane caulk stay as flexible once cured as silicone? I've never used any polyurethane caulk but the PL construction adhesive seems like good stuff.
    Last edited by Curt Harms; 07-30-2017 at 7:55 AM.

  11. #11
    The ones I did recently I followed these instructions. Worked fairly well...........To quickly cut a perfectly centered ."
    groove in the edge of a workpiece, set your
    tablesaw’s fence to position the saw blade
    just to one side of dead center. Cut a kerf, flip
    the workpiece end-for-end, and cut another
    kerf. Check the fit of the plywood in the
    groove and adjust the fence if necessary. If
    you use a thin-kerf blade (with teeth less
    than 18" wide), you may need to adjust the
    fence and make a third cut to remove the
    middle material. Use a featherboard to
    ensure consistent cuts, and always test your
    setup in scrap before cutting the actual
    workpieces.


    To


  12. #12
    I just make multiple passes, although I usually don't do it on the router table, I do it with a dado stack. Long ago, I took a piece of MDF and made slots with every possible combination of dado blades and shims. Now, I can just fit my wood to the slot, then I know how to set it up.

  13. #13
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    Slot it on the table saw and you can size the slot by making multiple passes.

  14. #14
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    Quote Originally Posted by Wayne Lomman View Post
    Run it twice with the 3/16 cutter, adjusting it for correct fit for the second run. This gets you the result without costing you another cutter. Cheers
    +1. You can actually get a more accurate fit this way. If you ply isn't exactly ¼" but your cutter is the panel is still not going to fit properly. I usually cut 3/4" dadoes with a ½" bit using the material as a guide.

    You don't have to get this fancy - I just screwed mine together using scrap, but this video gets the idea across:

    "Live like no one else, so later, you can LIVE LIKE NO ONE ELSE!"
    - Dave Ramsey

  15. #15
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    The ply may be 5.5 mm and even that will vary a little. When I was faced with oversized slots, I put masking tape on either side of the slot for a few inches either side of center then put a little silicone caulk in the groove, not too much so it doesn't squeeze out. That holds the panel but there is some flex. Never had a finishing problem and no rattle.
    I substitute Space Balls for the caulk. Way less mess & no chance of squeeze out or silicone contamination.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

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