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Thread: Cutting Square Holes

  1. #1
    Airmutt's Avatar
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    Cutting Square Holes

    So what is the best technique for cutting square holes in plywood. Some say drill out the corners and then cut to shape. Others say use a forstner bit to hog out the center and then cut to shape. Not sure I see if one is more advantageous over the other. Some even suggested using a chisel to square up the corners.

    Additionally, I purchased Bosch Clean Cut blades for my jig saw but the sales rep suggested using metal blades “ more TPI reduces chip out”.

    Looking for for advice on how to proceed. Thanks

    Dave

  2. #2
    Auburntsts's Avatar
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    As you indicated, there’s multiple ways to skin the cat. I typically use the drill the corners and jig saw the sides out method-fast and simple. Another method would be with a router but I’m guessing that would be overkill for what you’re wanting to do.
    Last edited by Auburntsts; 11-25-2019 at 08:15 PM.
    Todd “I drink and know things” Stovall
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  3. #3
    DaleB's Avatar
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    I also drill the corners and cut with a jigsaw. You have the choice of square or radiused corners that way.
    Measure twice, cut once...
    scratch head, shrug, shim to fit.

    Flying an RV-12. Building a Fisher Celebrity.

  4. #4
    Mike Switzer's Avatar
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    No matter what kind of drill bit you use, use a piece of scrap as a backing board when you drill the holes to eliminate any chance of tearing & chipping on the backside. Working with plywood, I prefer a file over chisels. (Chisels work great with regular wood, not so well with plywood) Pull the file in from the outside edges of the hole, if you push the edge out it may chip out.

  5. #5
    FlyingRon's Avatar
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    How big of a hole are we talking about?

  6. #6
    planecrazzzy's Avatar
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    Ever heard of a three sided bit that drills a SQUARE hole...

    Works with aluminum ...it would work with wood too.

    Gotta Fly...

  7. #7
    Airmutt's Avatar
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    Flying Ron, Talking about cutting holes for spars in plywood ribs.
    I’ve seen a computer model of the three side bit , but haven’t seen any for sale.
    Wonder if anyone has used a mortising bit to square cut the corners or does the chisel portion of the bit damage the plywood???
    Dave Shaw
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    Learn to Build, Build to Fly, Fly for Fun

  8. #8
    FlyingRon's Avatar
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    I've got a mortiser. Can't say I've ever attempted to cut plywood in it, but I guess I can fire it up today and see what happens. Generally, I when I'm cutting rectangular holes, I make a single hole and use the jig saw. Yeah, you might have to experiment with different blades (how thick is the plywood we're talking about?). If you're good and you have the room you can even plunge in the jigsaw blade.

    If you want fast and you're doing a lot of the same one, you can make a template and use a router. You'll then come back with a saw (I might even use a japanese-style pull saw) to square it up.

  9. #9
    Airmutt's Avatar
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    I’m talking about 1/4 inch plywood (marine grade).
    Dave Shaw
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    Learn to Build, Build to Fly, Fly for Fun

  10. #10
    Auburntsts's Avatar
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    Although like Ron I’ve never used a morticing bit on plywood IMO it should work just fine. I’d just use a backer board to prevent tear out on the backside.
    Todd “I drink and know things” Stovall
    PP ASEL - IA
    RV-10 N728TT - Flying
    WAR DAMN EAGLE!

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