Cutting Square Holes

[Airmutt]

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

[Auburntsts]

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.

[DaleB]

I also drill the corners and cut with a jigsaw. You have the choice of square or radiused corners that way.

[Mike Switzer]

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.

[FlyingRon]

How big of a hole are we talking about?

[planecrazzzy]

Ever heard of a three sided bit that drills a SQUARE hole...

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

Gotta Fly...

[Airmutt]

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???

[FlyingRon]

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.

[Airmutt]

I’m talking about 1/4 inch plywood (marine grade).

[Auburntsts]

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.

[kenryan]

I’m talking about 1/4 inch plywood (marine grade).

For that job I would use a router. With a router all your holes will be exact copies of your master template, insuring a perfect fit.

[planecrazzzy]

Never did find out how big this square hole was...

It would make a difference about how it was approached ...

This was drilled at the corners so I could FIND the hole after the Mahogany skin was epoxied in place

The router with a bearing pilot for a guide , made EASY work of cleaning the edges

Later I cleaned the corners with a file.

Gotta Fly...

[Airmutt]

Try 3/4”x 4 1/4” for starters. All corners are square.

[Kyle Boatright]

Try 3/4”x 4 1/4” for starters. All corners are square.

Dave, what are you cutting? Ribs for the Fly Baby, or???

You're always welcome to use any tools I have.

[rwanttaja]

Dave, what are you cutting? Ribs for the Fly Baby, or???
Don't have to cut square holes for stock Fly Baby ribs. They're formed of three separate pieces, joined by a cap strip.
http://www.bowersflybaby.com/tech/template_header.jpg

Ron Wanttaja