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Forum topic by Wendybird posted 04-14-2016 06:27 PM 587 views 0 times favorited 9 replies Add to Favorites Watch
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Wendybird

36 posts in 661 days


04-14-2016 06:27 PM

I am thinking of building a bed like the oeuf perch twin bunk bed. I like that the bottom bed can be used separately. Im wondering how sturdy the top bunk would be with the plywood legs? It would need to be pretty strong, my daughter is almost 11 and son is 4 and they sometimes share the current twin loft bed. Also wondering how i can fasten it altogether that it can be disassembled for moving, since we are a military family. I would attach pictures but I can never get them to work, google images has a lot of pictures of it. Thanks in advance


9 replies so far

View CaptainSkully's profile

CaptainSkully

1427 posts in 3018 days


#1 posted 04-16-2016 02:37 PM

Hey Wendybird,

The top will be super sturdy made out of plywood. It looks like you may able to make a lap joint where the stretchers meet the uprights. If that was assembled with short screws or some other take-down furniture type of fastener, it would be strong and easy to move. The joint would be of 2 layers of X thick plywood, so the entire bed would be 2X thick, but that will make it feel substantial. For example, two layers of 5/8” plywood (which is thick enough to get some screws into), will yield a bed 1-1/4” thick, which will look and feel sturdy and also large enough to round over all the edges. Good luck, hope that helps. Please post a build blog of your progress.

-- You can't control the wind, but you can trim your sails

View lew's profile

lew

11334 posts in 3215 days


#2 posted 04-16-2016 05:44 PM

I agree with Capt. Skully about overlapping the connections but I’d use bolts instead of wood screws- but that’s just me.

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View JBrow's profile

JBrow

814 posts in 380 days


#3 posted 04-16-2016 09:44 PM

Wendybird,

The photos of the oeuf perch twin bunk bed where the lower bed is separate from the structure of the upper bunk poses some difficulties from a structural stand point. The upper bed’s long legs could have a fair amount flex allowing lateral forces to weaken the joints where the bed rails join the legs. It is a long way to fall and so it needs to be sturdy. I envision Mom, Dad, and the two kids squeezed on that top bunk reading a book.

Plywood could be a good choice since the legs seem to curve 90 degrees into a short section that is parallel to the floor and onto which the upper bed’s rails are joined to the legs. Solid wood at the 90 degree transition could split under load (i.e. kids horsing around on the top bed). I would think a single layer of ¾” plywood would be insufficient structure. One layer of ¾” plywood could have too much flex in the long upper bunk legs and could allow the bed rail connection to weaken. Two layers of plywood would probably be enough.

My approach would be to create a mortise and tenon joint during lamination for the bed rail/leg connection. If three layers of plywood are laminated, the mortise could be a closed mortise whereas a two-ply lamination would result in an open mortise. The closed mortise would be stronger. Using counter-bored bolts in threaded inserts would make the bed rail/leg connection strong and more durable, but screws could also work.

The other concern is the flex or wobble that could exist in the upper bunk if no lateral bracing is installed on the lower section of the legs. The lateral bracing could be rails (the wider the better) parallel to the bed rails that connect the legs at each end and one long rail connecting the legs at the back. Joinery for these lower rails could be the same method used to join the bed rails. These lower rails could be 12” to 24” up from the floor.

There are other options for bed rail connections which allow the rail/leg connection to be a butt joint. I would personally avoid the bed rail connecting plates (steel bed rail fasteners) for the upper bed, typical on many commercial made beds. This system largely depends on gravity to hold the bed rails in place. The bed rail bolt system would provide a strong connection, especially if two bolts are used. The picture shows the bed rail bolt in use. The problem I see with bed rail bolts is that the medallion that covers the bolt on the leg would probably get bent given this project is for the kids.

http://assets.rockler.com/media/catalog/product/cache/1/image/720x720/9df78eab33525d08d6e5fb8d27136e95/3/7/37928-02-1000.jpg

The raw edges of the plywood could be sanded and finished or a hardwood strip used to cover the raw edges. If the bed gets a painted finish, using trim screws to reinforce the laminations would strengthen the laminations and limited the number of clamps required when gluing the plywood laminations together. The screw heads countersunk slightly below the surface could be filled with wood filler before painting. Applying wood filler to the plywood edges and then sanding smooth would limit the telegraphing of the plywood edges through the paint.

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CaptainSkully

1427 posts in 3018 days


#4 posted 04-19-2016 04:34 AM

Good stuff, lew! Threaded inserts into the back half of any lap joint, followed by a possibly countersunk machine screw would definitely meet the structural and portable criteria.

With all due respect to JBrow’s accomplishments and efforts, I think we’re over-analyzing things a bit. The compressive strength of any plywood that could reasonably be used for this project (e.g. 5/8” – 3/4”) will never fail under the loads of humans occupying the top bunk (divide 1,000 pound load by 4 legs = 250 pounds per leg = no problem). To make the bed thick enough for mortises would mean the bed would weigh hundreds of pounds and not be very portable. And now your betting the farm on the shear strength of a small tenon instead of a large lap joint.

-- You can't control the wind, but you can trim your sails

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Wendybird

36 posts in 661 days


#5 posted 04-19-2016 04:45 PM

Looking at pictures from this website ( http://www.mommasgonecity.com/2012/02/three-peas-in-a-pod-our-nursery/ ) it appears that the white rails make up a second layer of plywood for the upper legs and the other horizontal part (coming up blank on the name of it). Think the legs would still need 2 lays ply? Or would there me a better way to have the bed disassemble?
I’m now considering the legs being the only part that comes off, and having them glued up into the 90 degree angle with screws or dowels. I cannot do mortise and tenons yet and I’d rather not deal with the struggle on a big project, as I am a perfectionist and it would bother me.

View JBrow's profile

JBrow

814 posts in 380 days


#6 posted 04-19-2016 09:05 PM

Wendybird,

Your current leanings toward gluing the box together in which the mattress sets, making this a single structure, could make moving the mattress box difficult, especially if a tight turn is required. I lot would depend on the height of the mattress box sides. If you go in this direction, some additional structure could be included to keep the mattress box from racking during a move.

It also sounds like you would like to use single layers of plywood for the legs. Since the legs consist of two pieces of plywood joined at right angles, the compressive strength parallel to the grain of the vertically oriented plies in the plywood would probably be sufficient to support upper bunk weight without buckling. But that is only one of the design considerations.

The design challenge is the transfer of a weight from the bed to the legs and keeping everything tied firmly together, especially when the bed shakes while being used. If you go with an open leg design (no lower rails to tie the legs to each other), the resistance to the legs splaying outward and resistance to anti-racking forces would depend entirely on the strength of the joint between each leg and the mattress box. It is not at all clear to me how to make this joint as strong as I think it needs to be without laminating plywood that makes up the leg assembly. I would fear that just screws and/or bolts holding the mattress box to the single ply legs probably would fail over time.

If the legs are made up of two layers of plywood, a half lap joint (described above) incorporated in the legs when laminating the plywood together would transfer load directly from the mattress box to the legs all the way to the floor. Gluing three layers of plywood together forming an open mortise (like a slip joint) during the lamination glue-up would be an even stronger joint, since the open mortise would capture the mattress box. While CaptainSkully is correct, the legs would be heavier with 3 pieces of laminated plywood than with 2; it would be only 3 times heavier than a single layer of plywood. Since the open mortise is formed by cutting the center piece of plywood shorter than the outer pieces, it is straightforward to construct. But in the end, whichever design you go with, the strength and durability of the joint of the bed rails to the legs is, in my view, critical. These joints will see a lot of stress.

View Wendybird's profile

Wendybird

36 posts in 661 days


#7 posted 04-19-2016 09:59 PM

thank you jbrow. I get it now. I had trouble visualizing it before. I can see it now.
I wonder do you think making the bottom bunk first would be easiest? that way you are building around the bottom bunk and not trying to make the bottom fit under the already built top?

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Wendybird

36 posts in 661 days


#8 posted 04-19-2016 10:04 PM

I found this too. It looks like the bottom bunk is attached to the legs of the top bunk, but also unattached. http://www.oeufnyc.com/Instruction_Manuals/2013_US_Perch_Bunk%20Bed.pdf

View JBrow's profile

JBrow

814 posts in 380 days


#9 posted 04-20-2016 02:46 PM

Wendybird,

You could build the bottom bed first, but if you have accurate drawings from which you build the beds, it will not matter. My preference is to build the complete project, in this case, both beds at the same time. There may be some parts that use the same setup for part used on the top and bottom beds. Working on both at the same time can save a little time and enhance consistency of the parts. Additionally ensuring everything will fit together properly is a little easier when built at the same time. But in this case, building one then the other allows the finished bed to be moved out of the shop and put into use.

Perhaps my experience with building bunk beds could be of some help. I built bunk beds for my boys some years ago. The beds were exactly the same, copies with one exception. On the bottom bed ½” diameter holes about 2-2/2” deep were drilled in the top of the posts. The same size hole was drilled in the posts for the top bed, but at the bottom of the leg posts, where the posts meet the floor. A 5” long x ½” steel rod dropped into the holes in the bottom bed and the top bed slide down over the steel rod. These rods kept on upper bed from sliding off the bottom bed. In my case, the posts were about 3” x 3”.

But since I did not like the idea of always having to stack the beds one on top of the other, and also built an elevating frame on which the upper bed would set. One bed could be elevated on the frame while the other bed could be in a separate bedroom.

The head board and the foot board of the beds were permanent assemblies. Separate long bed rails were installed to connect the head board and foot boards and form the platform where the mattress would set. Three slats spanned the distance from one long bed rail to the other. ½” plywood set on the slats and it supported the twin size mattress. The boys are grown and out of the house and the beds went with them.

I learned from this project that the connection between the head and foot boards and the long bed rails is critical and must withstand a lot of force

The assembly instructions were very informative. I assume you were hoping to simply copy Oeuf’s design. Once you establish the dimensions of each piece and gather the hardware, replicating the design would be straightforward. However, after looking at the list of safety precautions, methods used for assembly, and requirements for mattress size, I would avoid copying their design. For example, the company recommends only one child sleep in the upper bunk and that the child should be under the age of 6 years old. After looking at their method of connecting the long upper bunk rails to the legs, I understand the upper bed weight limit. Therefore, designing your own bunk beds, copying design elements you like, will likely give you much more functional, durable, and sturdy beds that can be used for years.

Explicitly identifying your design requirements will drive the shop drawings that are used when building the beds. These include the look of the finished project and how it will be used. A couple of examples are 1) tapered legs with sweeping curves where the long rails meet the legs and that 2) the beds must be usable independent of one another. Also recognizing the limitations in the shop is important. A fully equipped shop affords more options in the design, while limited tools and skill would require a carefully thought out design. The design will have to adequately address each of the requirements and constraints.

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