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I am building a new bed for the missus for Christmas. She liked this bed from ikea:

joining compound angled dowels with a dowel

The problem is where the headboard connects to the legs. The legs/headboard piece are both 1.5 inches in diameter. I decided to join those two parts with a half inch dowel, about two inches long. That made it easier to attach the pieces (the compound angles were a nightmare). Are there any concerns that resting our backs against this headboard will sheer the headboard from the feet of the bed?

If it is a concern, any ideas of how to reinforce it after they've already been joined together?

Btw, the bed is made of cherry (even though the image below shows maple).

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  • If I had to use just one dowel I would go with something closer to 1" (25mm) even though this makes the side walls thin. But if using a steel bolt or other steel fastener is out for some reason I'd much prefer to go with two dowels as it's not just the sheer strength of the dowel that you need be concerned with. There are rotational forces to counter, which is why workbench rails often feature a stub tenon in addition to the bolt they're held with, or a dowel underneath the bolt.
    – Graphus
    Commented Dec 20, 2019 at 7:01
  • Useful discussion on dowel strength in the Comments (under both Question and Answer) here, woodworking.stackexchange.com/questions/9723/…
    – Graphus
    Commented Dec 20, 2019 at 7:02
  • I would suggest a 1/2" aluminum dowel, bent to the angle and extending 3"-4" in each direction into the individual leg piece on each end, set in epoxy. I suggested aluminum since it is a little easier to bend than steel, but should still be strong enough.
    – Ashlar ♦
    Commented Dec 25, 2019 at 1:45
  • A technical point: it's not shear stress that is at question here, but it is bending stress. The inclined headboard is acting like a cantilever beam and needs more than a butt joint reinforced with a relatively small diameter dowel to avoid failing. I would avoid sitting in bed reading, and I would be careful about pushing it against the the wall.
    – Ast Pace
    Commented Dec 27, 2019 at 18:33

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I don't think a dowel is going to handle the directional stress. If you look closely, I'm pretty sure the designers have used some sort of lap-joint, possibly reinforced with a metal fastener, and not a continuous piece of stock. You might be able to download the instructions for this bed and see how those parts intersect with other parts.

Or, the factory makes a piece of just over the total length of the leg and headboard using some sort of lap joint, which is then machined down to that profile. Ikea is really good at taking what is essentially scrap and turning it into dimensional pieces and panels. (As someone who has reused an entire Ikea baby room set and turned it into other stuff, it is amazing what you find inside a ripped-down panel!)

But to get two pieces to handle stress as if they were a single piece, you have to get long grain lined up with long grain. Dowels are ok for some sort of joinery, especially those where you are gluing up panels and want to use dowels for positioning, or to stiffen up a long glue line or a mitre. But they are rarely considered a significant part of the overall joint strength.

For your purpose I don't see there being enough glue strength to keep that joint from turning into an unexpected and sudden hinge. And, to be clear, it is the glue that you want to depend on, not a 4-inch piece of crenelated softwood that you hope has expanded properly into the hole surrounding it.

Now, a lap-joint with dowels or splines through the lap would be really strong, assuming your primary glue joint is made up of a fair amount (more than 2 inches, certainly) of long-grain faces.

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  • A couple of comments. I viewed this at ikea itself, and it is NOT one solid piece of wood, and they appeared butt joined together from the outside (which is why I suspected there was a dowel there). Downloading the plans was a great idea. I checked them out and they show one solid piece. So maybe they used a wood dowel, metal dowel, or mortise and tenon. Also, the dowel I used was hardwood and there is long grain to long grain contact via the dowel.
    – dfife
    Commented Dec 19, 2019 at 21:05
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    @dfife I suspect that we aren't seeing the inside of the join, then. Maybe there are hidden fingers or something. I just don't see a butt-join having the strength for this application.
    – user5572
    Commented Dec 19, 2019 at 22:00
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    Anyway, it's super hard to tell from this picture, but it sure looks like there is a stepped lap of some sort -- which would be the ideal joint for this application! When I look at the higher-res images from Ikea it sure looks like a stepped lap, but at any rate there is almost certainly something more than a 4-inch dowel in there.
    – user5572
    Commented Dec 19, 2019 at 22:06

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