Knack for cutting interference-fit framing lumber?

[Sukhoi]

I've always wondered about this. On home improvement TV shows, usually when opening up a wall to add a header for an opening, they install studs or the beam itself that are perfectly sized to fit with a couple sledge whacks. How do you know exactly what length to cut it to and then make it happen? There seem to be so many sources of error between the tape measure where one end of it they're reading along a curve, pencil thickness, blade kerf, general circular saw inaccuracy, and who knows what else.

 

[jmagg]

From what i've just read, interference fit pertains to assembles without fasteners. Framing tolerances are less critical since they are nailed together.

 

[Greenman]

1/16" tolerance is pretty easy to hit. 1/8" you can do with your eyes closed. On critical cuts you decide if you want to leave the line or take it when you measure.
It's called rough framing for a reason.

 

[iRONic]

How many takes did they shoot before you saw that perfect fit on that show?! 🤣

If you aren’t a carpenter by trade or severely inexperienced framing and you cut to your line you may be grabbing another piece of lumber.

Just cut a sixteenth shy of the line.

 

[Sukhoi]

Good point, hadn't considered multiple shots.

Sounds like it's a combination of there's enough margin for error and with enough experience it's easy to fit in that margin. So you aim for your target from the beginning, and not add say 1/8" by default because you know you're going to take off more than you wanted somewhere in the process?

 

[Greenman]

Good point, hadn't considered multiple shots.

Sounds like it's a combination of there's enough margin for error and with enough experience it's easy to fit in that margin. So you aim for your target from the beginning, and not add say 1/8" by default because you know you're going to take off more than you wanted somewhere in the process?

The only thing you add or subtract is the thickness of the pencil line. If you're doing a bunch of repetitive cuts you set up a miter saw with a stop.
I've watched a few framing videos and never once seen anyone tighten up their plates or blocking. Something I've always done.

 

[skyking]

When you get into the groove, measuring the place you want to install the board with the same tape that you use to set up the cut, with the saw that you use every day, it is easy.
Until you get tuned up, you nibble at it with the miter saw a few times.
I cut cabinet face frames to 1/64 with a pencil and tape. It takes me a while to get there.
it also takes glasses these days.

 

[Sukhoi]

When you get into the groove, measuring the place you want to install the board with the same tape that you use to set up the cut, with the saw that you use every day, it is easy.
Until you get tuned up, you nibble at it with the miter saw a few times.
I cut cabinet face frames to 1/64 with a pencil and tape. It takes me a while to get there.
it also takes glasses these days.

Makes sense. I was thinking about my original question more, and I think it's mostly how do people get such an accurate reading when using a tape measure like this pic?

It's probably what you said about getting in the grove, but it just seems hard to measure in that corner to 1/16". And then you have people doing that same sort of measurement for studs where you can't even look straight on at the end without getting up on a ladder or putting your face to the floor. Now maybe the TV people are doing one of those two things before the glamor shot when they can magically read that number perfectly from 6 ft away.

 

[Red Squirrel]

If I have a ton of cuts to do, I usually make a jig where I can get the perfect size every time without having to measure each one individually. Then I will cut a few mm longer than I think I need in case the jig flexed a little or I was still off somehow, then I will hammer it in.

Since factory lumber is rounded it does make it a little tricky to get a super precise measurement with just a measuring tape as when you're reading the line there is no 100% definite way to know which one is at the actual edge, and it depends what angle you're looking at it from, you might be in some weird tight spot.

I also don't bother trying to measure stuff out in imperial, I don't know how people do that, way easier to use metric, don't need to deal with fractions on the fly, just measure to cm then count the lines for mm. Come up with a way easier number in your head to deal with than imperial crap. But if you have a lot of the same type of measurement to do I find making a jig is the best way to be dead on each time.

Here's an example of a jig I made for framing my garage, it's basically just a 2x2 that slides into another 2x2, I would use a clamp to lock it in place once I got my measurement.

 

[Sukhoi]

Was that a door filled in with whatever masonry someone could find in the trash pile?

 

[Red Squirrel]

Was an old fireplace chimney - fireplace was in the living room on the other side. I didn't care about how it looked since it's being covered anyway. I was basically reusing cinder blocks that came from the chimney. Also bought me a lot of extra room in the garage, every square foot counts, it's super small in there. Turning it into a shop.

I was kinda toying with making some kind of access door so I can get into the garage from inside the house but opted to just cover it.

 

[Sukhoi]

Ah that makes sense and explains that black area

 

[Greenman]

That seems like a lot of effort to get a perfect fit that will only be perfect for a few weeks. The lumber drying and changes in humidity will amount to more than the error in your measurements.

The other issue that often gets overlooked is the cumulative errors when fitting studs that way. It's easy to find yourself driving the plates up and building a hump in the wall. I always set a string line or a laser as my reference point.

 

[hardhat]

How to make studs the same length:
1. measure and cut one stud the correct length.
2. stack long board on the bottom with cut board on top. Put the ends of both boards against a wall or something vertical.
3. mark the length of the top board on the bottom board.
4. cut to remove all of your mark, hopefully with a miter saw.

 

[Red Squirrel]

It's easy if you are building a wall from scratch (ex: an outside wall to a new building) as you don't really need to have the top plate fit to anything existing, so in that case, you just cut all the studs the same size and build the wall then raise it up. But for an inside wall it's trickier as the floor/ceiling may not be perfect across the board. But yeah you want to avoid driving the top plate too much or it will pull out from the studs you already installed.