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I'm making a swing supported by nylon rope to hang under a deck. The swing seat will be 17 in. wide and made from pressure treated pine. Can I use a 1x6 (left over from making the deck)?

isherwood
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Bmurph
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    A swing for use by children wearing shorts or swim suits? Consider the risks of skin contact with pressure treated wood. https://www.mass.gov/service-details/pressure-treated-wood-use-in-playground-equipment – MTA May 17 '23 at 11:34
  • Is it actually a 1x6, or is it 5/4? – isherwood May 17 '23 at 12:50
  • A 1x6 in the US would be even smaller: More like 3/4" x 5 1/2". I'd say way too small for even a small child. I also doubt it would be very comfortable, as compared to an actual swing made out of rubber or plastic (but kids rarely mind that). – Eilon May 17 '23 at 18:43
  • I'm guessing the deck board is actually a 2x6 and not 1x6? That would be more typical. And, it would be much stronger for a swing seat. But pressure-treated wood wouldn't be the best choice. – Colin D Bennett May 17 '23 at 20:56
  • @Eilon kids can sit on harder (especially flat) surfaces than adults because they exert less pressure – Chris H May 18 '23 at 12:24

2 Answers2

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A 1x6 pine board isn't great for a swing. It's barely adequate from a strength perspective, and any large knots or other flaws severely compromise that strength. Also, one-by boards are much more prone to splitting at the rope holes than even slightly larger 5/4 decking boards.

I would consider doubling a 1x6. You could screw the layers together outside the rope holes. I wouldn't put fasteners in the seating area in case of a break. Or just stack them loosely and secure with a knot above the swing.

I also like Criggie's idea of using "stringers" at the ends--crossgrain reinforcement at the rope holes would alleviate much of my concern.

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isherwood
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    I think all commercially available wood glue is waterproof, so gluing the boards together would work, or just go with a 2x6. And don't forget to round over the edges for less chance of injury or snagging fabrics and skin. – computercarguy May 17 '23 at 19:25
  • @computercarguy some isn't very waterproof, but gluing is certainly an option – Chris H May 18 '23 at 12:24
  • If you wanted to screw together, even outside the rope holes, I'd use countersunk (sometimes called flathead) machine screws from the top, with flanged nuts on the back, M6 to M8 (1/4"-3/8") They'll avoid sharp points even after years of weathering. Outside the area that's actually sat on you could also use coach bolts, again from the top; these are common in commercial play equipment – Chris H May 18 '23 at 12:27
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If you have the wood already, lay two scraps of wood 17 inches apart and parallel to represent the ropes, then put your board on top. You'll be close to the ground for this test. Extra length can hang out the side without compromising this test.

Then stand on the seat. Does it deflect noticeably? If No then jump on it. Stomp on it. If a full sized adult can't cause noticeable deflection, then it'll be fine for an adult or several kids to swing on.

If you're small, ask someone else to stand on the board with you. Better it breaks before assembly.

Of course you will also want to test your ropes as well, using similar methods. This is how pressure vessels like gas tanks are tested - push them to much-higher than standard and if they leak, they fail.

If the seat fails testing, then consider making it double thick with two equal sized pieces screwed/glued together.

You could also add one stringer or two apron boards underneath. This gives the seat more mass too, which helps the rider keep swinging.

Criggie
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    I like this test, but note that ropes run through the board will weaken it further – Chris H May 18 '23 at 12:28
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    This isn't a valid test unless the stringers are added to the swing. All the pressure will be concentrated around the ropes, which can result in the splitting I mentioned. At that point the whole thing falls apart. -1 for that. +1 for the stringer idea. That would resolve most of my concern. You might lead with it. – isherwood May 18 '23 at 12:42