Carpentry -- making the perfect window cutout

August 10, 2007 7:41 PM

Carpentry puzzle: Imagine that you have a wood-framed window opening (example). Exterior sheathing completely covers the frame. How exactly do you cut through the sheathing?

This has long vexed me as one of the more complicated carpentry problems I've run across.

I'm guessing that instead of trying to cut from the inside that it's better to cut from outside. I would go inside, drill a hole in the 4 corners of the window frame through the sheathing, go outside, draw lines connecting all the holes, and cut along this exterior line.

OK, but here's the proble: how do you start the cut? A circular saw sounds like a bad idea, especially since you'd have to hold the blade guard open. Any kickback and you'd be toast. You can't start a jigsaw into solid wood either. So what tool is needed here?

I'm guessing to do the line cuts, I'd want a jigsaw. Circular saws are dangerous IMHO on vertical planes.

Then, how would you clean up the sheathing edges to conform to the frame? I'm thinking an electric planer would do the job.

Commands and any alternative ideas to this problem would be appreciated.

posted by antipasta_explosion to grab bag (19 comments total)

I think this is why they invented the Sawzall / reciprocating saw. Jigsaw is kind of wimpy.

You drill a hole to start it, if you don't have an edge.
posted by smackfu at 7:52 PM on August 10, 2007

With good technique, it's fairly easy to start a cut with a Sawzall without a starter hole. You start at a very shallow angle, and gradually work the saw to perpendicular.
posted by pjern at 8:11 PM on August 10, 2007

Agreed on reciprocating saw (sawzall) with a drill starter if you like.
posted by true at 8:14 PM on August 10, 2007

If you don't mind putting forth a little elbow grease, you can get much nicer edges with hand saws. A traditional Japanese dozuki saw would make quick work of this, and because you can readily vary the pressure, speed and angle of your cut, you should be able to cut cleanly, without splintering, which is hard to do with power tools. But even a flexible flush cutting saw would be adequate for this task, if it is just a one-of.
posted by paulsc at 8:26 PM on August 10, 2007

When I was a kid, my dad would have solved this using a "saber saw", after drilling a hole. (picture at the bottom of this page.)
posted by Steven C. Den Beste at 8:34 PM on August 10, 2007

I had this problem not so long ago and did what everyone else is suggesting: I used a reciprocating saw. I guess I'm a wuss, because I used a drill to start the holes (from the inside, of course). I used a handsaw to clean up the edges where they stuck out a little past the framing.

A jigsaw would do the job, but a reciprocating saw is much easier. Unless the cut was really ugly, you only really need to clean up the bottom edge (since your window shouldn't be flush along the top or sides).
posted by ssg at 8:52 PM on August 10, 2007

If you are a tough guy, you (as you mentioned) drill your four holes and drop lines.
Then you take your circular saw (I'm not saying to do this. Only even think about it if you have used a circular saw every working day for five or more years. Do not do this.) and plunge cut it into the line. Because you use your circular saw every day you know what it will do. You know how not to torque it so it won't kick back and you shelled out a little extra to buy one with a foot (? the plate you rest on what you are cutting) that is rigid enough to not flex and torque while you are cutting. And you never work with a dull blade. Ever. You never knew how much these little things mattered until one fall when you were framing out houses upstate and recognised the value of that extra seventy-to-a-hundred bucks. That old guy was not just an asshole.
Plunge-cutting cleanly is not that hard to do because you know your circular saw (because you've used it every day for years) well enough not to be fazed by any of its quirks and can just use it to do what you want done.

The ends of the cuts, near the holes, are going to have to be finished with a hand saw. Because you've been doing this for years, you know that a jig saw is not the right tool for this, but a good mixed (rip and cross) cutting hand saw will let you cut out the last bits quickly and easily. You (naturally) keeps this saw sharp and would never let the blade rust.

It is kind of hard to plunge cut on a wall, but you keep your body calm and stable, concentrate, and only move the saw with your arms and it's not only doable, but fast and easy.

If you are not a tough guy and just want to rip open the hole, bust out the sawzall and go to it. Make sure to wear goggles because if you buy cheap blades they fly pretty far pretty fast when they break and there is a chance of one catching an eye. I lost a thumbnail once. You can start a cut without a hole, but start it off the line you want to be the finished line. And pay close attention - the saw-z-all is mostly a demo tool and wanders like a bitch.
The saw-z-all will tear open a good enough hole and then you can do what-ever else you're gonna do there.

(most) Japanese saws are better than ninety percent of the people who wield them. Some of these saws don't like plywood though, as the saws are very smart and brilliant at what they do but are designed to do specific things perfectly (which they can, in the right hands), and not necessarily all things well. Plywood, being a mish-mash of woods, needs a versatility most of these saws are not designed to handle.
posted by From Bklyn at 8:57 PM on August 10, 2007 [1 favorite]

Yeah, heroics aside, I would plunge cut with a circular saw. You can either just put the front edge of the base on the wood and lower the spinning blade into the cut, or you can set the base at its maximum forward angle, leave its nut just slightly loose, and then put it flat on the wood and lower the spinning blade through the base.

But you can plunge cut with a jig saw easily too, just put the front edge of the base on the wood, start the saw, and lower the blade into the wood - here's a video.

The kind of Japanese saw you'd use to start a cut in the middle of a flat board is an Azebiki.
posted by nicwolff at 11:10 PM on August 10, 2007

Oh, and wear goggles and gloves, and keep your face out of the blade plane.
posted by nicwolff at 11:11 PM on August 10, 2007

I always use a circular saw and plunge cut as described above. This is easier with a worm drive saw because you control it from the back and it is less likely to kick. (Then again, I permanently locked up the blade guard to get it out of the way which makes things easier, but I wouldn't recommend that for most people.)

Also, I usually cut and attach the sheathing before standing up the wall. It's a heck of a lot easier.

If you mark the window openings as you put on the sheathing, you don't have to guess where the corners are. You just snap lines and cut.

Never bother using a handsaw to finish the corners. Just cut a half inch or so beyond the corner with your circular saw and you're done. You have little kerf marks in the corners, but who cares. It just rough sheathing that will be covered by the finished window frame.

Given all that, if you aren't comfortable using a circular saw, the other methods mentioned might be better for you.
posted by JackFlash at 12:41 AM on August 11, 2007

Heroics aside? Dude, chicks dig the heroics.
posted by From Bklyn at 5:50 AM on August 11, 2007

Obviously, there’s more than one way to skin a cat, but I’ve always seen this done by plunge cutting from the inside with a sawzall. It takes about 2 or 3 minutes per window. Some carpenters are better at it than others but, as long as you get it flush, neatness doesn’t count for much as its going to be covered by house wrap and a window frame.

I tend to save plunge cutting with the circular saw for places where neatness counts, like the sidding board under the window.
posted by Huplescat at 6:40 AM on August 11, 2007

The sawzall will suit you. If you have no experience in plunge cutting with the circular you will be too timid. And the sawzall is a handy tool for many other tasks, it's good to have.

Re: rough edges - having the sawzall follow the lines on the outside (if they are snapped right and follow the framing) will be all you need. Your new window will overlap the edge enough, you wont need to plane it down.
posted by Kensational at 7:46 AM on August 11, 2007

From the outside use a Router with a pointed flush cut bit. It's the easiest, fastest, neatest way to do it. Don't go to home depot, go to a real tool supplier and they will set you up with the right bit. Just plunge through with the point and and go to town.
posted by sgobbare at 11:32 AM on August 11, 2007

And THIS is the bit to use. Sorry I should have posted this with my original blah blah. Over and Out.
posted by sgobbare at 11:55 AM on August 11, 2007

Thanks for the Amana Panel Pilot Bit. Now that I know about it I need one. But we may be in danger of overthinking a plate of beans.

One of the first solo jobs a promising new guy on any framing crew gets is cutting out the window openings from inside with a sawzall. Its challenging to do it nice, almost impossible to ruin, and a clever initiate can learn a lot about carpentry by doing it.
posted by Huplescat at 7:15 PM on August 11, 2007

Frankly, I don't know any framing crew that cuts window openings from the inside. They cut them from the outside with a circular saw and they almost always do it before standing up the wall. However, that is different from the OP, who has no choice at this point and a sawzall would probably do the trick.
posted by JackFlash at 8:19 PM on August 11, 2007

">ZZ
posted by Huplescat at 8:23 PM on August 11, 2007

That’s great, JackFlash, because your answer implies a different way of framing a house from what I know. Maybe its another geographical thing. Back in the seventies carpenters in the East learned a lot from the West Coast guys who went thru the building boom there in the sixties. But I think we’ve caught up now.

Do you do “Breaktime” on the “Fine Homebuilding” website?
posted by Huplescat at 9:10 PM on August 11, 2007