The square, the tape, and reading the wood before you cut
Okay. Your pine's had a few days to sit in the garage now, acclimating, doing whatever it is wood does when it's getting used to your house. Now we get to the part I actually think is the most important part of the whole class, and it's not the cutting.
It's the looking.
Get a real square first
I mentioned this before, but I want to say it again because I believe it. Buy a decent square. Not the little plastic one that came free with a tape measure set. A real combination square or a speed square, something with an actual straight edge on it that isn't going to flex.
Mary got me one for my birthday years ago, and it's still the tool that changed the most for me. Before that I was eyeballing right angles and wondering why my pieces never lined up right. Turns out I wasn't cutting crooked, I just had no way of knowing if I was square in the first place. You can't fix what you can't measure.
You don't need five squares. You need one good one and you need to use it every single time before you cut, not just when something looks off.
Measure from one edge, every time
Here's my actual opinion on measuring, and it's a little different from what you usually hear. Everybody says "measure twice." I think that's not quite the right advice, or at least it's incomplete. Measuring twice from two different spots on the board just gives you two chances to be wrong in two different ways.
What I do instead is pick one edge of the board, usually the end that looks the straightest, and measure everything from that same edge. Every single cut line on that board gets measured from the same reference point. That way if I'm off a little, I'm off consistently, and consistent is something you can work with. Two different starting points stacks your errors on top of each other and you don't even know it happened until the shelf's crooked on the wall.
Which, by the way, is exactly what happened to me on my very first shelf. Measured from the wrong end of the tape on one side. Cut a quarter inch short. I hung it anyway. It sat on my wall for four years before Mary finally asked why one edge dipped. So I'm not telling you this from a position of never having done it wrong.
Reading the wood before you touch a saw
This is the part people skip because they're excited to start cutting, and I get it, I do it too sometimes. But before you cut, run your hand down the board. Look at it from the end. Look at it from the side, sighting down the length like you're looking down a rifle barrel, and see if it's bowed or twisted at all. Pine moves in our dry air more than you'd think, and a board that looked flat at the store might've cupped a little just sitting in your garage this week.
Look for knots, because a knot near where you're planning to cut can make the wood tear or the blade wander. Look for the grain direction, which way the lines run, because that tells you which way the wood wants to split and which way it doesn't.
And look for hardware. Screws, staples, nails, anything metal that might be hiding in there, especially if this is reclaimed wood or something that's been sitting around a while. I cut into a board once without checking first and there was a screw buried in it I never saw. Put a nick right in a brand new saw blade. I still have that blade, it hangs on my wall in the garage now, and every time I look at it I remember, look at the wood before you cut it. Not after.
Mark it, don't guess it
Once you've got your reference edge and your square, mark your cut line with a pencil, not a pen, something you can see clearly but that doesn't leave a permanent mark on wood you might need to erase and remeasure. Use the square to draw the line straight across the board, square to that reference edge. Don't cut on the line, cut next to it, leaving the pencil mark on the piece you're keeping. I'll show everybody exactly what that looks like on a scrap piece when we're all together, hands next to yours, not on your project. I don't touch anybody's board without asking first.
I did a little woodworking with some kids once, building a bookcase for my friend Alexandria's family, and I let her youngest hammer in the last nail. It went in crooked, good and crooked, and everybody looked at it and just decided to leave it. That bookcase has one crooked nail in it on purpose now and honestly I think about that a lot when I'm being too careful about a mark that doesn't need to be perfect. Some of this stuff matters. Some of it really doesn't.
The stuff on this lesson does matter, though. Square and measuring, that's the foundation part. Get sloppy here and it shows up in every board after it.
Before next time
Get your square if you don't already have one, and practice marking a few lines on a scrap piece of pine, always measuring from the same edge. You don't need to cut anything yet. Just get comfortable with the tool in your hand.