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Best way to cut openings in 3/4" plywood

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Forum topic by MrRon posted 550 days ago 2358 views 0 times favorited 34 replies Add to Favorites Watch
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MrRon

2723 posts in 1844 days


550 days ago

I am doing a project that requires me to cut 8 openings in 3/4” plywood. The opening sizes are 16”x30” and 14-1/2”x16”, 4 openings of each size. The openings will be covered by cabinet doors. I have 3 ways of accomplishing this. I can use a scroll saw; plunge cut on a table saw and finish the corner cuts by hand; Use a router with a template. I’m inclined toward the router method, but I don’t have a bit long enough, but I can go buy one. If I go with the router, I suspect I will have to make several passes at increasing depths. What do you think is the best way? I’m a bit leary about using a saw as I can easily get off line and ruin the cut. As the sketch shows, the openings are spaced far apart, too far to use solid lumber and I need the grain to run vertical.


34 replies so far

View nwbusa's profile

nwbusa

1016 posts in 887 days


#1 posted 550 days ago

I’d probably use a jig saw and then clean it up with a router pattern bit.

-- John, BC, Canada

View Loren's profile (online now)

Loren

7253 posts in 2248 days


#2 posted 550 days ago

Make hollow templates carefully to make them square and
straight-sided. I like 1/4” hardboard. You could also find
a may to make mitered templates out of thicker stock
which would get you out of filing the inside edges
straight. Mark out the holes and cut them out inside
the lines with a jig saw. Then use your templates and
a top-bearing flush trim bit to clean up the sides.

You could also avoid the templates and just use a
straight edge clamped to the work to trim the edges.
This method might be more appropriate if you want
the edges of the 8 top and bottom holes to come
out perfectly aligned.

-- http://lawoodworking.com

View Dallas's profile

Dallas

2856 posts in 1088 days


#3 posted 550 days ago

Use a template and the router. Depending on your router you wouldn’t want to cut 3/4” deep in one pass. With my 2 HP I go that deep in 3 or 4 passes depending on the material.

When you get the holes cut clean up the corners with a sharp (SHARP) chisel or even a jig saw if you have a good one.

Good luck.

Someone else will probably come along with an easier way to do it, but this is how I’ve done it for years.

-- Improvise.... Adapt...... Overcome!

View pintodeluxe's profile

pintodeluxe

3271 posts in 1414 days


#4 posted 550 days ago

Well usually face frames are hardwood, so this is a unique problem. Why do you need so much of the cabinet face to be solid, as shown in your picture? I think I would design it with a face frame, which can be easily built with a pocket hole jig.

If you need it to be built as pictured, I would cut the rough openings with a jigsaw. Then come back and pattern rout the openings to final size. If you cut to within 1/16” of your layout line with the jigsaw, you should be able to clean up the cut in one pass with the router. The pattern for the router can be built from scraps. Just make a square or rectangle, and screw it together with pocket hole screws. A bearing guided router bit will ride the pattern for a perfect cut. Leave the corners rounded, or square them up with a chisel.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View DS's profile

DS

2131 posts in 1021 days


#5 posted 550 days ago

Mr. Ron, for me, historically, I would treat this front panel as a giant face frame.
The Rails and Stiles could be solid wood, or, they could be banded plywood.

You could use dowells or a Kreg jig to make the joints and I’m pretty sure, you will use far less material to accomplish your desired result.

You say you need all vertical grain. I guess I don’t understand why that is.
I suppose it’s possible to veneer the entire front.

Then again, careful skill saw cutting gets the job done in a pinch.

Proof again that there are thousands of ways to “skin a cat”.

Don’t suppose you have a CNC machine—that would be a slick method too. ;-D

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View shipwright's profile

shipwright

4843 posts in 1399 days


#6 posted 550 days ago

Skilsaw (sorry, circular saw) and a guide on the good side of the cut. If you wander you wander into the waste. Second would be a jigsaw but that’s much slower.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View Matt Przybylski's profile

Matt Przybylski

433 posts in 979 days


#7 posted 550 days ago

I would make two templates, one for each size of hole, out of 1/4” hardboard. I’d make the non-hollow portion of the template a bit longer and put a cleat at the end then I can butt it up against e edge of the panel and know that every square will end up being the same distance down the panel. Line it up to some vertical lines to line up the width of the template. Before doing this I’d cut a rough opening with the jig saw and then apply the template, clamp/double sided tape it to the piece and rout the perfectly square portion then go back and chisel out the corners for a perfect square.

-- Matt, Illinois, http://www.reintroducing.com

View jim C's profile

jim C

1452 posts in 1699 days


#8 posted 550 days ago

What am I missing here?
A Bosch jigsaw will fly through that, and no corner work is necessary.

-- When I was a boy, I was told "anyone can be President", now I'm beginning to believe it!

View AandCstyle's profile

AandCstyle

1257 posts in 858 days


#9 posted 550 days ago

Lay out the piece of plywood with extra width. Cut it into strips on the TS corresponding to the sides of the openings. Crosscut the strips that need to have the openings to correspond with the tops and bottoms of each opening. Glue the strips back together in the correct order and use biscuits or splines to strengthen the joints. Clear as mud?

-- Art

View CessnaPilotBarry's profile

CessnaPilotBarry

877 posts in 711 days


#10 posted 550 days ago

I’d use a router, templates, and the smallest spiral bit I could find. If you make the templates right, they can be indexed against the top and bottom edges for perfectly straight holes.

The spiral bit will leave a perfect face, the templates support the shear, and the smallest diameter will leave the least corner cleanup. With a small bit, there’s no reason to precut holes. Think “RotoZip”...

-- It's all good, if it's wood...

View jim C's profile

jim C

1452 posts in 1699 days


#11 posted 550 days ago

Jonathan,
I disagree with all of it.
In order of your statements:
1. Draw the lines, it only takes a 1/2 hour for that whole piece.
2. I know how to tilt a saw, but drilling a hole take seconds.
3. I can “walk” the saw into every line/corner from the original first cut.
4. No blade drifting with a good, modern, jigsaw (Bosch) and I think you meant perpendicular (not flat)

Please explain the table saw method, as I’m trying to understand how this can be done accurately without seeing the underside, as well as over cutting the square at the bottom.

-- When I was a boy, I was told "anyone can be President", now I'm beginning to believe it!

View RogerInColorado's profile

RogerInColorado

286 posts in 555 days


#12 posted 550 days ago

I’m in the router with a template, template guide and spiral bit camp. The cut will take a whole lot less cleanup

View runswithscissors's profile

runswithscissors

894 posts in 626 days


#13 posted 549 days ago

I think Art, and a couple others, are on the right track. Make it a face frame in the usual way, but using plywood boards rather than solid. I had a scheme something like yours in mind when I made my workbench. But after I got everything marked out (I think I even had started making some of the cuts), I realized I wasn’t going to have a lot of plywood left, just a lot of holes. So I did ordinary face frame. Your horizontal pieces can simply be made as crosscuts on the plywood, giving you the vertical grain (But I, too, am not sure why that matters to you). Also, you’ll be left with a fair chunk of usable plywood. And biscuits work very well for joining in that kind of structure.

View jim C's profile

jim C

1452 posts in 1699 days


#14 posted 549 days ago

Jonathan
I thought you might explain the table saw method for those of us without the experience.

-- When I was a boy, I was told "anyone can be President", now I'm beginning to believe it!

View waho6o9's profile

waho6o9

4749 posts in 1177 days


#15 posted 549 days ago

Plunge saw like a Festool, or a home made version.

Clean up as needed, easy peasy.

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