So how much did your traditional Japanese futon sofa bed cost then?

It's pretty easy costing the parts for the sofa bed. 

The nuts, bolts and screws cost around 1500 yen. The wood cost 4,000 yen. The wheels cost 400 yen.

The guy made a mistake with the washers, charging me 4 yen for a bag of 25, when in fact the cost is 4 yen each. I could have got away with 9 or even 8 mm bolts rather the 10s, which stick out a fair way. This cost more than I saved on the washers.

The labour costs are a little more tricky. I spent at least half an hour getting the wood, and that was after about five trips to DIY shops wandering around looking at parts and scratching my head! 

Then perhaps around eight hours looking at bits of paper and scribbling on them. 

Internet research: two hours. Conservative estimate. Difficult to tell exactly since I was doing it in and among other, more general internet research.

Total design time: ten hours. 

The sawing, drilling and assembly of the nine main parts of the frame took about three hours. I'd bought them in the morning. I was in the shop about an hour, spending far too much time working out which bits of wood to buy so that I could cut all the pieces out of them. They had a cutting service, but only at right angles, so I was going to be on my own for the 73 degree angles of a lot the parts. 

Then there were the fiddly bits, cutting off the corners, trying to plane curves around the edges, then trying sand paper before realising that a rasp was probably the right tool for the job. Make that seven trips to the hardware shop. I had to go anyway because I only got 8 wing nuts the first time.  Actually, perhaps I should have got a spoke shave, or cut the curved parts with a jig saw.

After assembling the frame downstairs, bolting parts together then screwing the slats on top, I had the great idea of unbolting it into two pieces to make it easier to carry upstairs. It was easy unbolting it, but a real challenge to put it back together since the slats had begun to take control of the frame.

Total direct labour around 8 hours. Call it ten to include visits to the shop. So insulting myself with a near minimal wage of 900 yen per hour, the labour cost would be 9,000 yen. Added to the parts, that makes around 15,000. If I include the design costs, it goes up to at least 25,000 yen. 

For readers of this blog, I'll be happy to charge 15,000 yen though. Send in your orders below!

Actually I had to get some tools too. I guess these should be covered somewhat even though I still have them. Well, I dropped one of the new drill bits I got onto the stone tiles and the end broke, but it still works. 

But who's counting? I had a lot of fun and a great sense of satisfaction!

Also there was an opportunity to teach the kids some woodworking basics, which will have been a good thing as long as they never do any woodwork. The kids were sometimes useful, although at their age they spent more time getting in the way than helping, and when they were helping, they took more time in supervision and fixing what they did than they contributed in useful work. It was helpful having them looking at the drill from two different directions to check it was vertical, and they did some useful sanding, getting some of the edges smooth.

A New Tradition of Futon Sofa Bed

The futon sofa bed is now working, and here are some reflections on the design. I can make some modifications and address some of the issues, but really I'd really like to make another one. To justify this I'd need to buy another futon, of course. 

The front should probably be higher. I kept the angle to about 7 degrees, so the base is around 20 cm off the ground at the front. This height is great for kids, or at least would be if their upper legs were longer, since the chair part is quite long. They seem to sit on it quite happily, when it's not being used to accumulate crap.

Another issue is that the back is vertical, and the frame at the back of the chair is a right-angled triangle. When you sit back, this rocks a little and I think an isosceles triangle, more like an A-frame, would be more stable. As it is there is a chance of it banging back into the wall behind. 

So geometrically speaking, I probably should have made the back a little taller and at more of an angle, the front a little higher, and the seat and middle seat-back sections a little shorter. 

As I predicted, it is possible for a small child to open the sofa into a futon, but after pulling it out half way, it crashes down with a large amount of noise and power, and the health-and-safety part of me is worried about other children's fingers or toes getting in there. So some kind of damping would be a good idea. It may be possible to get more sophisticated hinges, but these are likely to work in the wrong way. I'd like something that will provide more resistance the faster it moves, but simple damping on the hinges is likely to be the opposite and resistance will decrease as it gets faster. 

Also as predicted, putting the futon back into sofa position requires two hands, or a long arm, as the middle part needs lifting a little before it is pushed in.

It may be possible to work out a strap and pulley system that would both control the descent of the A-frame, and facilitate its return, but I think that's going to take at least another month, 12 envelope backs and ten sides of A4.

Also the spacing of the horizontal slats is a bit wide, and I think I need to increase it by three or six. There are four fixed slats, at the end of each of the movable parts, so they can only be increased in multiples of three. Currently there are 13 90 mm slats, with gaps of around 80 mm between each, which are big enough for little feet to push into when they are walking along the futon on top. Another three slats will bring the gaps down to about 45 mm, which should be small enough. Six extra slats will give a gap of just 25 mm, which may not be big enough to allow it to fold up properly.

Spruce, the material I used, seems quite stiff and pine may have been more springy. 

Since I last looked, another kids' futon seems to have found its way between the frame and the futon on top, which has made the seat a little more comfortable. It has also created a home for another piece of loose soft furnishing that was floating around the house, which was the main job of the device. Perhaps it can attract even more bits of soft furnishing, and solve the height and leg-length problems too!

Plans for a Traditional Futon Sofa Bed

Here's the design. Sorry it's not in CAD! That's one technology I've never really got into. Also, I haven't drawn all 13 planks that go across, but I think you can get the idea. And sorry that I wrote on it while I was working out what lengths of wood to get.

The problem with a lot of the commercially available futon sofa beds is that they don't seem to realise that the sofa is likely to have its back to the wall, and when you turn it into a bed, you just want to pull it away from the wall into the space in the middle of the room, and not have to faff around moving the base in and out. This is not so difficult, but maybe I've just thought about this more than everyone else!

Even if the sofa does not have its back to the wall, the chances are that there will be a space in front of it which could be turned into a space to sleep. If not, then they don't really want a sofa bed, they want a futon cupboard. Perhaps a traditional Japanese futon cupboard. These come free with every traditional Japanese house. 

Also, in terms of design criteria, it's going to be in the children's room, so I want something that a seven-year-old can turn into a bed, but that won't collapse if a ten-year-old and two of his mates are jumping on it. This is more of a challenge, but I think doable!

There are wheels on the floor-ward end of the seat. When the seat is lifted up, these should make contact with the ground, making it very easy to pull the seat forward, turning the A frame into a flat bed. It will be very difficult to do this when someone is sitting on the sofa, since the wheels are going to be pushed away from the ground by their weight, so I hope the wheels will only come into action when they are needed for conversion. 

I'm hoping the weight of the frame, and the angle of the middle section as it meets the ground, will keep the back robust. If not, a latch can easily be retrofitted to lock the frame in the sofa position. 

Putting the bed back into sofa position may be a two-handed job. Although the wheels are going to go back quite happily, the other part of the bed may need lifting up a little before it starts moving. We'll have to see how it works when it is made!

The materials I've used, by the way, are 2 by 4 (89 x 38mm) spruce for the frame with 89 x 15mm planks on top.

Designing a Traditional Futon Sofa Bed

We have a double futon that we don't usually use and it's kind of tricky to find somewhere to put away. So at the moment it's folded into three and sitting in the kids room doing a rather poor impression of a couch. It's doing a very good job collecting toys and dust, since it's directly on the floor, and is creeping, gracelessly and lopsidedly, away from the wall.

What we really need is a base for it that will convert from a couch into a bed. So I'm in Japan, and you'd think that it would be really easy to get one. This is the land of futons, right? Everyone must have one. 

Well, actually... 

Traditional Japanese futons go on tatami mats. These are traditional Japanese floors. If Japanese people get rid of the tatami mats or build houses with wooden floorboards or carpets, as they increasingly do, they get beds. If they want to sit on something other than the floor, they get sofas and couches. 

There is no such thing as a traditional futon sofa bed. Futons, sofas and beds are from different traditions. 

So, to the drawing board and then to the shop to get some wood. As usual, I start the design process with bits of paper and crazy ideas, then, a few sheets later, I start looking on the internet to see what there is and how they make it, and find nothing ideal but many things inspirational. Then, several sheets later, the ideas become more detailed, and the designs become more simple as solutions to problems take away the causes of the problems.

Like the legs, for example. The problem with having the futon on the floor is that you can't sweep under them. So this means the frame needs legs.

There are two basic designs of futon sofa beds: bi-fold and tri-fold. In the bifold, the length of the futon is the width of the couch, and the back basically falls back horizontal to make the bed. This is good if you want the couch to be as wide as possible. We don't, so we're going for the trifold, in which the width of the couch is the width of the bed, and frame and futon are both kind of folded into three to make the couch. 

The back of the couch is made up of two of the parts, in a kind of A frame, with the other part sticking out to sit on. It looks something like the picture below.

So I started with some legs at the front, then the legs of the back part tucking underneath it, and some legs under the middle hinge, the one opening upwards. It seemed like a good idea to have a leg under this hinge, to stop the bed collapsing at that point. The other hinge opens downwards, so if there is an adequate stopper on it, once it opens to 180 degrees it won't go any further, even if you put weight on it. This all means that when the bed is open, there are three sets of legs along its length, one set at each end, and one a third of the way along. Not ideally balanced, but it should work. 

When it turns into a chair, the legs at the front of the chair are still active. The ones at the back are now sticking in from the back at around  horizontal, hopefully not getting in the way. The middle legs are sticking towards them, the back of the seat now being held off the ground by an extension of the middle span. 

But why not get rid of those two legs, and have the existing legs swing out of the way when it's bed time? Then there are less legs to worry about, it doesn't matter which way the hinges go since the whole of the frame is lying along the floor. Functionally, this is going to spend most of its time as a couch rather than a bed, so being able to clean under the bed is not a problem. 

Simple is best. As Antoine de Saint-Exupery said, "A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." 

And yes, I could have just followed 

Bored Guy's excellent instructions here. Or bought something online for slightly higher cost. But actually it's the design part that I enjoy. 

In fact rather than making my traditional futon sofa bed, I may just design a few more. 

How to design a chair: ergonomic data from Cornell.