Many iterations of a plywood stool that requires no glue

cnc-router-stool-design

At his local hackerspace [Vincent Sanders] noticed an interesting problem. The stools that they had were great in most cases, but there was one workbench which was very much the wrong height for them. So began his quest to design and fabricate plywood stools which use no glue for their joints.

The Cambridge Makespace (in the UK) turns out to be a perfect environment for this type of project. They already had a CNC router which can cut the plywood pieces, and there are other members who were willing to help train [Vincent] on the equipment. He found a design on Thingiverse which fit the bill, except for the actual measurements. He needed metric units to match the sheet stock available to him. Once converted he put together a stool that didn’t work at all. The thickness of the plywood just didn’t mesh with the tolerances of the joints. After wandering around to different suppliers in town, digital calipers in hand, he came up with a range of actual thicknesses and adjusted his joint design accordingly.

Of course this wasn’t the last revision. Even with the joints working the seat was still a little rickety. He moved to the next plywood thickness offered, redesigning the files to match. His final stool works like a charm, with five or six of them fitting on one standard sheet of plywood.

Comments

  1. Paul says:

    Great, now that I don’t need glue I can finally build a stool! Let me just fire up my CNC router…

    sarcasm aside; I admire the dedication and the success ultimately.

  2. richnormand says:

    Nicely done.
    You might want to revise your design to a four leg stool if possible. You will find the three leg stool inherently tippy and they are actually now banned in our labs.
    Cheers

    • Tony says:

      3 legs bad, 4 legs good?

      What bizarro world are you living in?

      The astronomy & photography worlds, among others, wait with bated breath for why they should throw out their tripods, and use, erm, quadods instead.

      • andarb says:

        Probably something to do with beer-fridge hacks in said labs. :)

      • richnormand says:

        I would suggest you look at modern ergonomics standards for industrial furniture and workplace safety rules then. Unless, of course, you are the type who likes to climb on top of your telescope equatorial tripod stand….. I’ll go get a beer now!!! Cheers.

      • t says:

        3 legs are good for leveling, not stability. Imagine how much of a pain it would be to adjust four legs to level; you have to shorten two at any time to have any hope of haste.

        If you draw a perimeter around the stool legs, and then lines from center of the stool to the perimeter, you will notice the three shortest lines are much shorter than the four shortest (something like a lever for the stool to resist your arse with). If you put a force along one of those lines, you’ll notice the weight will transfer off of one of the legs much sooner with a tripod than a four legged stool.

        Also three legged stools have to have a shorter base, otherwise the legs might interfere with your own or the seat would be awkwardly wide. As proven by tables and couches, this isn’t a problem for four legged furniture.

        • Tony says:

          Given a similar area for one to plonk ones arse on, the legs on a 4-leg stool will be vertical, while those on the 3-leg stool will splay out.

          The ‘splay out’ bit gives the 3-leg stool a better centre of gravity, however that same property make them take up more space, hence unpopular amongst publicans due to the reduced arse-to-bar ratio.

        • Blue Footed Booby says:

          The point of tripods isn’t leveling; it’s that a three legged stand can…stand without wobbling on a rough surface. Leveling is a side benefit.

      • Galane says:
    • There is a five leg version because of this very reason ;-)

      The current one is pretty stable in general use but seems I need just one more iteration…

  3. Rich says:

    Does the UK have personal injury lawyers? How long will that ring hold up with people putting their feet on it, standing on it, etc.? Plywood does not have a lot of strength in tension or bending in a piece that shape.

    YMMV but I would not want something like that for a long-term shop fixture.

    • Chris C. says:

      I gotta agree with you about distrusting that ring. Plus it would suck to lift it up by the seat to move it, and have the legs possibly fall out of their slots. A bit of glue or some kind of fastener is warranted there.

      I love the simplicity and economy of the design, but like most cheap modern mass-produced furniture, it’s only strong in one direction. Avoiding things like that is the reason I DIY in the first place, so mimicking it seems odd to me.

      • The ring is perfectly usable a a foot rest but bends a fair bit if you stand on it.

        The chance of the legs falling out is nill, you need a rubber mallet and a *lot* of force to remove them after fitting. I designed the interference fit very carefully so this would be true.

    • Tony says:

      Plywood is stronger than you think, and the entire point of plywood is to give strength to a piece like that.

      Whether that piece will support 100kg or so (a person standing on it) is another matter, if not make it thicker. It’s not hard to check.

  4. Rusty Shackleford says:

    Looks like a lot of waste in their cutting layout.

  5. Vonskippy says:

    So is there a glue shortage in the UK? Why the glue aversion?

  6. t-bone says:

    How do you pick the stool up? Also, be careful if you’re sitting back with a leg between your legs. On second thought, splurge! Use some glue.

  7. Hirudinea says:

    This could put Ikea out of business, just CNC your pattern into the plywood at the plant and flat ship a load of them to the store, all the customer needs is a cheap hack saw. (Hey don’t laugh, people buy cheap crap from Ikea!)

  8. echodelta says:

    Could actually work with Baltic plywood or other hi-grade stuff.
    Lawyers sit on 4 legged stools, never 3.
    Just like Buttericks, cut and sew/saw.

  9. In the wood working world, glue is considered cheating and to compensate for something poorly made and requiring assistance. I admire the thought behind the design, including the material strength, type and design concerns. Good job for working within the confines of a problem. And more legs being better? Hmmm, … I think the height to width ratio, or the center of gravity location would be a better way to measure.

    • SATovey says:

      >>>
      In the wood working world, glue is considered cheating and to compensate for something poorly made and requiring assistance.
      >>>

      That is complete and total nonsense. Typically; brads are used to hold joints together until the glue dries, and doing so enables the project to last much longer than if it were held together with nails that ultimately loose their grip as the wood dries and shrinks causing those nail holes to enlarge.

  10. sqelch says:

    surprised no one mentioned the glue used to laminate the plywood

  11. Dax says:

    The irony is that the full metric size plywood sheet, 1220 by 2440 mm is almost exactly 48 by 96 inches, or 4×8 feet, give or take a couple hundreds of an inch. Even the 12 mm thickness corresponds to 1/2 inch imperial plywood, because the actual imperial standard half inch plywood is in reality 15/32 inches which is almost precisely 11.9 mm. You can’t even manufacture plywood to within 0.1 mm tolerances because humidity makes it swell and shrink.

    He didn’t actually need to convert the designs because the construction and woodworking industries are all using imperial stock, only measured in metric, same as with plumbing, tools etc. where a nominally 19mm socket is actually a 3/4 inch socket.

    That’s because you can usually find a metric size that fits so close to the original imperial size that they simply keep the tolerances around the old size, manufacture the old size, and stamp a metric size on the label.

    • Dax says:

      For example:

      “There was a brief pause in proceedings to discover 18mm sheet is actually 17.7mm and needs a 17.5mm slot to make the interference fit work.”

      The EU standard (EN 315) specifies the 18mm thickness as between 17.1 – 18.7 at 10% moisture. It’s actually within the imperial 3/4″ ply, which is actually 23/32″ with 1/32 inch tolerance.

      • Nicholas says:

        Maybe he didn’t have an Imperial ruler or tape measure :-)

        • Dax says:

          Whenever you see metric figures that look like they might be evenly divided by three, or are very close to something that is, you can pretty much guess that they’re based on imperial measures, because that indicates that there’s a foot hidden in the figure somewhere. That’s because a foot is roughly 30 centimeters (304.8mm)

          It’s also useful to remember that an inch is roughly a quarter of a decimeter. (25.4mm) so for small measures, things that are close to divide by four might actually be inches, or thous/mils as they tend to be in electronics.

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