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I've never built something from scratch before, and thought I would start with a small and simple project. Except I'm not sure of all the physics.

I want a bedside seat with a shelf for books. It needs to be able to hold probably at least 150 pounds on the shelf, in addition to the weight of a person on top.

I would like the shelf to be raised maybe 1 1/2" - 2" off the floor. I would also like the seat to be comfortable, but with the option of holding a cushion.

...I would also like it to not fall apart on me after using it due to poor design.

I'm thinking about using a strong plywood for most of the bench (sides, back, shelf), but real wood for the seat (maybe maple?), and maybe a little bit of cedar at the bottom under the shelf (perhaps in the corners to help a little with weight).

I also haven't decided on the best methods for attaching the pieces. Maybe camlocks and screws?

I sketched a few design ideas (the perspective is completely off and it's not to scale, but I just wanted to get the ideas down).

What physics should I think about regarding bench designs for holding weight at both the seat and on a shelf?

Prospective bench designs

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  • Hi, welcome to StackExchange but this Question is a little too open-ended to fit really well with the SE model. 'Sturdiest' and 'best' are also problematical words to use in any query here, since this invites potential respondents to make a value judgement — likely to lead to opinion-based answers.
    – Graphus
    Commented Apr 15 at 9:00
  • "strong plywood for most of the bench (sides, back, shelf), but real wood for the seat (maybe maple?)," As already highlighted you have to be careful using solid wood alongside plywood. It is perfectly doable, but beginners/learners frequently aren't up to speed on how to do it without causing issues. "maybe a little bit of cedar at the bottom under the shelf (perhaps in the corners to help a little with weight)." Do you mean to help reduce the weight of the unit, or to help take the weight? If it does happen to be the former I wouldn't worry about that as there's so little difference.
    – Graphus
    Commented Apr 15 at 9:05
  • "Maybe camlocks and screws?" Why instead of some form of proper joinery? There's nothing inherently wrong with camlocks for a specific use-case, but that's it: they're best for lighter-duty furniture in the Ikea model, where the ability to break down the furniture (not just so that it can be sold as flat-pack furniture in the first place) is one of the fundamental requirements. Building at home largely sidesteps that requirement and for this project specifically I see no need for them at all. In addition 1, they inherently introduce some weakness... [contd]
    – Graphus
    Commented Apr 15 at 9:13
  • ...because parts aren't as firmly attached as otherwise (i.e. any alternative involving glue). And 2, they are specifically counter-indicated when solid wood is to be joined to a manmade board; highlighting what I said about beginners/learners not being up to speed about how to mix the materials without introducing an issue.
    – Graphus
    Commented Apr 15 at 9:15
  • 1
    I will STRONGLY recommend against cam locks. It is very difficult to get them lined up just right without CNC machining, and if they're not lined up just right, they don't hold very well. I created a cabinet using cam locks (in an attempt to match factory-made cabinets) and it looks horrible because my machining wasn't nearly precise enough. It's securely holding loads of paper & other things, but... meh.
    – FreeMan
    Commented Apr 15 at 12:42

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There are 3 things I would consider for this type of structure.

Will the seat hold the weight without bending too much?

You can use this calculator to select appropriate material and thickness: https://woodbin.com/calcs/sagulator/. Obviously, adding a middle support helps, as it halves the effective span of the seat.

Will the whole thing rack (wobble side to side)?

Some of your designs have a back attached (I assume, plywood). This is good and will prevent racking.

Will the joints be strong enough?

For this type of plywood construction, glue and screws or dowels and screws should work. Do not skip the glue part. Additionally, your designs 2 and 3 put much less stress on the joints because the seat rests on the vertical members. I think this is the way to go. Here’s how this goes wrong: https://www.reddit.com/r/vinyl/comments/2qlzbe/psa_please_setup_your_expeditskallaxs_correctly/

P.S. If you use solid wood for the seat, you can’t screw/dowel and glue it to plywood sides, because unlike plywood, solid wood expands and contracts along its width (here, from front to back) throughout the year. A simple solution is to build the whole structure from plywood — seat included — and put the solid wood layer on top (you can, for example, attach it at the back only to allow for movement).

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