# Bed frame conundrum



## Dokkodo (20 Apr 2022)

Hi all. Been a while since i posted. I have a fun problem solving challenge, and thought it would be fun to use the hive mind.

I am building a sort-of mezzanine bed for a customer, which will be seen from below. He had an idea that he wanted me to build the frame that goes directly under the bed (which will be tatami mats and a futon - this mini remodelling project has taken on a japanese theme) in the style of the 'cradling' that 'old masters' picture frames sometimes used to build very large and very solid picture frames. It also ties in with the japanese look.

So I agreed it would be a fun design principle and have designed something along similar lines

This is it seen from below:






My question relates to the grid in the middle. The timber by the way is all yew(!) which is lovely to work and also annoying in that finding and getting useable sections out of even a big fat juicy looking board is difficult. Luckily he has access to a decent stash.

Material worries aside, the grid is currently drawn in 30mm wide by 45mm high sections. The sides are the narrower edges, the wider are head and foot boards. My current concern is how to join the grid to maximise rigidity over the span (6' both ways), and my options as far as i see it are *a)* dominos at all edges and lap all the internal joins, or *b) * dominos at all edges, keep all head to foot spans whole and domino each of the cross-wise 'noggins' in.

Pros and cons to each, both pretty laborious and obviously will require much focus while machining! I feel like half-lapped joints are weaker, even if they are all perfectly nice and snug and glued, because every single piece has its effective load bearing height halved, 22.5mm isnt much. But on the other hand there are a lot of them to spread the weight, and the one good glue face will count against this to some extent, and i wonder about offsetting the lap in favour of the downward facing joins that want to open up and reducing the height at the join of those below, which will want to pinch shut under pressure anyway.

The alternative, of putting a million dominos in everywhere, is very time consuming, but allows for greater material efficiency (can use up short sections of stock rather than needing lots of decent long ones) and leaves all spans full height, in one direction at least. The joinery will be aesthetically more forgiving, and yew is pretty stable but if those joints aren't all snug over time thats a visual and structural problem. A butt join and through domino (might machine up extra long small ones even) through each junction, glued across noggin ends, is more side grain glue surface, and feels like it might be stronger. However I cannot even begin to imagine how hellish that glue up would be!

This is all coming from intuition, which is why im asking. Im no structural engineer - I have under-engineered things in the past and it can be quite unrelaxing! So id be very grateful for opinions (other than, youre mad, its not going to work) and ideas, open to any other totally different approaches too.


----------



## Joshjosh (21 Apr 2022)

Looks like a nice interesting job.
If it were me I'd probably build it like a floor, with joists and noggins. But I'd use sliding dovetails for the noggins instead of dominos. I think once set up that'd be quicker and also allot easier to glue up.

I would be nervous with such small timbers spanning that length but that's just based on a gut reaction.


----------



## dzj (21 Apr 2022)

Does that grid lay on the floor?
A good question to ask when considering the strength of a bed is whether it can cope with the weight of 2 
boisterous, chubby people at once.


----------



## Dokkodo (21 Apr 2022)

It doesn’t lay on the floor no, it’s a more complicated than that... it’s floating, and counter weighted! the head and foot boards come down to rest on the top of some bookshelves. I’m going to epoxy a steel flat bar into each side member to be sure they can carry the weight across the span, yew seems quite flexible and the bits I had weren’t going to be reliable against a two big people having a pillow fight test.
That said this is just an occasional guest bed.

Sliding dovetail noggins is a good shout, they could be stopped so that from the bottom they look neater and are supported. Thanks, ill mull that over!


----------



## Jameshow (21 Apr 2022)

You need all I then to be full depth one way. Once you start notching them you weaken the drastically! 

Id go fill depth in the across wise direction as is typical on beds. 

The rest can be dowels domino buscuited to suit.


----------



## Jacob (22 Apr 2022)

For strength they'd have to be though in one direction, with no housings, notches, dominos. The pieces in between would have no structural function and wouldn't be easy to fit as the through pieces would bend differently.
Perhaps cut 3 of the through pieces at 30 x 45 and see how they would hold your weight resting over a saw horses at each end. Sounds a bit flimsy to me!
Maybe put the cross ways pieces also as whole lengths but crossing over, not interweaved.
So it'd be like a floor but with equally sized and spaced bearers going the other way under the joists.


----------



## Inspector (22 Apr 2022)

I would make the mattress supporting structure as a torsion box of 8, 10 or 12mm plywood with the "crate" structure between them 50 to 80mm thick and screwed to the bedd rails, headboard, footboards. Then I would make the "Shoji" screen as a separate decorative piece attached to the bottom of the plywood.

Pete


----------



## Terry - Somerset (22 Apr 2022)

Inspector Pete may be right.

Yew was the material of choice for bows - it bends.

You may like to try a single piece of yew supported 6 ft apart, and test the dead load it will carry in the centre without significant deflection.

Gut feel - if it won't readily support (say) 40kg, a 150-200kg active load spread over (perhaps) 3 "ribs" isn't going to work.


----------



## DBC (23 Apr 2022)

Inspector said:


> I would make the mattress supporting structure as a torsion box of 8, 10 or 12mm plywood with the "crate" structure between them 50 to 80mm thick and screwed to the bedd rails, headboard, footboards. Then I would make the "Shoji" screen as a separate decorative piece attached to the bottom of the plywood.
> 
> Pete


This is what I was going to suggest also. And as to the torsion box depth; you are building something load bearing in a residential dwelling so it should meet the code a la the joist span tables.


----------



## Dokkodo (27 Apr 2022)

Howdy all, good thoughts thanks. Yew is definitely bendy, been doing a few experiments and I can attest to that. I have started doing some of the job, and succesfully reinforced the side members of the bed with 5x50 flat bar, resined into a routed channel and inlaid over. Before i did that, there was no way id put my weight in the middle of one set over a 6 foot span. After, i held myself off the ground over the middle of one fine, i weigh maybe 85kg and it definitely deflected but was definitely also sound.

As for the central cradle structure. I like your idea jacob for its simplicity. However I dont think I can convince him of it aesthetically, the cradle is sort of the creative basis for the project in a way, the client is very much into design and architecture and (fortunately) appreciates that some of his requests take some figuring out, but he also wants what he wants! And im also happy to try and make the unlikely happen if possible, its quite fun to try in any case, if it doesnt work then thats just another challenge. The torsion box also could be a compromise, if I can maintain the look of the thing overall.

After Josh suggested sliding dovetail noggins i drew up the picture attached, thinking to cut stopped dovetails. To my mind a neat way to construct the thing and quite simple with a good jig and layout, and much nicer to glue up. Id probably domino the outside ones into place but could then drop the rest in from above.






Regarding the forces involved, im curious. I appreciate that under engineering something people are paying good money to sleep on (or worse, have guests sleep on) is not cool! But it seems to me that also, a lot of mass produced cheap beds have pony little slats. Yes, often supported halfway across... but certainly nothing like the rigidity of a torsion box. So some flex is ok, i wonder whether i could resin another couple of smaller steels into a couple of of the central members and preserve the original idea.... Also, the cradle is 1800x1800mm and made to snugly fit two tatami mats, about 60mm of rigid and dense fibre matting (also heavy, granted) which will distribute weight quite a lot, so unless you stood up on it (which you cant as its raised) I doubt youd get any critical concentrations of weight. Im open to being wrong, but keep the ideas coming if so!

On a related but interesting side note, ive been reading up a bit about longbowmen of yore. Their bows were also often 6 foot long or more, and made of yew.... One (totally random internet) source states that they got 80-120lb to 185lb of force to fire an arrow, with modern reconstructions gaining a range up to 330m! Which seems quite incredible, a third of a kilometer. I know noone wants to be launched a third of a kilometer out of bed in the morning, but it is reassuring...


----------



## profchris (28 Apr 2022)

Dokkodo said:


> Howdy all, good thoughts thanks. Yew is definitely bendy, been doing a few experiments and I can attest to that. I have started doing some of the job, and succesfully reinforced the side members of the bed with 5x50 flat bar, resined into a routed channel and inlaid over. Before i did that, there was no way id put my weight in the middle of one set over a 6 foot span. After, i held myself off the ground over the middle of one fine, i weigh maybe 85kg and it definitely deflected but was definitely also sound.
> 
> As for the central cradle structure. I like your idea jacob for its simplicity. However I dont think I can convince him of it aesthetically, the cradle is sort of the creative basis for the project in a way, the client is very much into design and architecture and (fortunately) appreciates that some of his requests take some figuring out, but he also wants what he wants! And im also happy to try and make the unlikely happen if possible, its quite fun to try in any case, if it doesnt work then thats just another challenge. The torsion box also could be a compromise, if I can maintain the look of the thing overall.
> 
> ...



I'd reinforce the central, longitudinal, member.

I bought a slatted bed, and with two on board we rolled to the middle!

A 2 x4 added in the middle and, even years later, each side is springy enough for comfort but without sagging in the middle. It's a standard double with 12mm thick slats, supported only at each side and the middle, to give you an idea of minimum bracing to hold 2 adults.


----------



## Fanous (21 May 2022)

Same as Pete, I would do a structural job for matrace, and a beauty peace under it.


----------



## Spectric (22 May 2022)

Build a frame with structural integrity and then as someone has said just make the grid a decorative piece that you see from below. This way the people don't end up on the floor below and you have more freedom in making the decorative part really decorative without havingto think about it's strength.

Another option is to make it like a big hammock, supported at both ends but then the grid part could be fancy linked hinges like knuckle joints, just a thought!


----------



## pe2dave (22 May 2022)

Could a heavy man be supported mid 'bow'? IMHO no.
ditto that structure with such spans (gut feel).
How (and how often) and with what would be my questions?
Such fine pieces, steel seems an obvious one... but how? Under tension?
I wouldn't take it on (and expect to be asked back).
How much face would be lost if the bed crashed with a guest or two in it?


----------



## Valhalla (30 May 2022)

How about routing out a channel in some (or all of the full width cross-members - say 7mm x 30mm ) and inserting some 6mm (or thicker - if there are no weight constraints) stainless steel flat bar into the channel (orientated vertically) or you could drill through and fit some recessed bolts and then cover them with timber plugs. You could perhaps fill the void with some epoxy resin (for additional strength) and then cover the channel with some form of yew lipping.

You could even engineer it so that the steel sat within the centre of the sliding dovetails


----------

