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I'm using salvaged wood and my project involves some boards sitting next to each other, so the bowing and crooking are easy to see.

I plan to nail 1x1's across the backs of the boards and anticipate that will flatten out the bowing. I have 1x2's I could use if the extra strength would matter.

Is planing their sides the best way to deal with the crooked boards? I think I see 3 or 4 boards to plane.

The floor in my apartment isn't flat enough to judge boards on. Is there an easy way to tell when I've got the edges flat or is making the boards match each other so there's no gap all I should worry about? salvaged boards 1x1s to be added behind

After turning and re-ordering the boards this is what the back looks like. I think adding a wood screw to 4-6 of those boards should resolve the bowing. gaps from bowing

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    "I plan to nail 1x1's across the backs of the boards" OK not what you asked about but, no, you don't want to do that. You aware of wood expansion and how you have to allow for it? In addition, these 1x1s may be/are probably insufficient to the task anyway.
    – Graphus
    Commented Feb 26 at 8:02
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    Also, a 1x1 nailed on won't hold against bowing, the boards will simply pull off the nails. A screw might work, but, note @Graphus' comments about expansion.
    – FreeMan
    Commented Feb 26 at 15:26
  • I was going to use wood glue and extra nails. I think I'll proceed like that but with 1x2's and add a wood screw where needed.
    – user66598
    Commented Feb 26 at 16:07
  • I'm also finding that re-ordering, flipping and/or rotating the boards so the bows and crooks go the same direction reduces the gaps and height variations a lot. So the back piece won't need to pull as hard to hold the boards together and I'm guessing the nails will be much less likely to pull out. Maybe screws are unnecessary now but I'd hate to omit them and find out later they're needed. i dunno what to do.
    – user66598
    Commented Feb 26 at 16:20
  • I'll probably add screws anyway. I posted a picture above so you can see what it looks like after re-arranging the boards. I definitely should have done that first. I'm still not sure they're in the best order but I was trying to keep them somewhat symetrical just for aesthetics.
    – user66598
    Commented Feb 26 at 16:57

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Is planing their sides the best way to deal with the crooked boards?

In general yes, planing would be fundamental to how one normally prepares boards for glueing up; preparing long edges would be one of the key reasons for the hand-tool woodworker to own a jointer plane (although it is doable to use shorter planes for this).

Where a power jointer is available taking any sort of irregularity like this out of one edge of a board is one of the things it's specifically for (the other being flattening a board's first face).

Terminology note: edges not sides. Boards have faces, edges and ends. "Side" can be unhelpfully vague because it may refer to a face or edge depending on the board's orientation or position.

Is there an easy way to tell when I've got the edges flat

Up to a point you can learn to sight down boards for a good-enough read on when you have something flat (both faces and edges) but ideally one compares to a known straight edge — either an actual straightedge (made or commercial) or some decent stand-in like a long aluminium level.

In terms of how you get there, in addition to the regular testing against a straight edge/straightedge this is where winding sticks are utilised. Although they don't have to be, winding sticks are pretty much universally shop-made.

How to make wooden straightedge and winding sticks

Source: Popular Science, Dec 1942

is making the boards match each other so there's no gap all I should worry about?

Sort of, but not generally in the way you're thinking. It's usually the angle of an edge one matches2 rather than planing one edge to match the irregularities of the next (as you might when fitting something to a wall, AKA scribing). Beyond that it's normally dead-straight edge to dead-straight edge.

However, sometimes (rarely) one might deliberately leave a pair of edges slightly hollow for what's called a 'sprung' joint; this is more relevant to hand-tool woodworking than it is to those relying on power tools (where they're not generally needed and harder or impossible to create anyway).

So how close to perfect is close enough?
Because wood is slightly flexible and glue joints are so strong — if done right they ARE stronger than the wood itself (see previous Answers for details) — within reason one can use clamp pressure to close up small gaps between boards when doing a glue-up. There's definitely some judgement required here but a useful rule of thumb is to consider any gap that you can close with hand pressure3 small enough that you don't have to take it out.... although do so if you have the time and gumption because it is better practice.

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1 Good enough for many purposes. But the higher-end the requirement, or the longer the surface, the more important it becomes to test rather than just rely on a visual read (although you should continue to test/practice this judgement forever if you're a hand-tool woodworker).

2 So for example if one board's edge is 90° the next needs to be the same, but equally if one is 88° the next needs to be 92°; these are referred to as complementary angles.

3 Although it's best if you never leave a gap near the ends because gaps are most likely to open up there over time; counteracting this tendency is precisely what the sprung joint was designed to counter.

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  • These boards won't be connected with glue or anything else and I can close all the gaps by hand. I thought about just putting a 1/4" gap between each board to hide the crooks but I'd rather not. My other ideas were to bend them straight against each other before nailing the ends or to use a plane and long straightedge. I think I like the last idea best.
    – user66598
    Commented Feb 26 at 15:08
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    Thanks for telling me about long straightedges btw! I remember seeing them now. I don't know if I'd ever use it again so I'd prefer to improvise with something I have already. String is my only idea so far.
    – user66598
    Commented Feb 26 at 15:09
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    If you don't want gaps between the boards, they don't have to be dead flat, they just need to have matching "hills" and "valleys". LEGO aren't flat on the bottom, the studs on the top of one LEGO go into holes in the bottom of another and that's what holds them together. Making tightly matched hills & valleys would be very difficult, but possible with enough effort. Probably impractical, but it's is one option. Not common because it's difficult. Also, for a straight edge, just use a steel ruler of required length. They can be had very inexpensively and can come in handy elsewhere.
    – FreeMan
    Commented Feb 26 at 15:30
  • Since I only have maybe 4 crooked boards I'm gonna try a thumbtack and thread. I did find a nice metal 72" straightedge for $15 with free shipping from Home Depot that will be my backup if the string doesn't work.
    – user66598
    Commented Feb 26 at 15:37
  • A string (pulled very tight) will work as a straightedge, but if you're going to be doing any other woodworking, you're going to want/need a nice straightedge, so I'd go ahead and order that 6' ruler/straightedge now anyway.
    – FreeMan
    Commented Feb 26 at 18:21

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