Thread: Window seat design alternative

Originally Posted by slickmick77

Apart from framing up a window seat can someone suggest an alternative. I've seen window seats made from cabinets but I'm not sold on it been structural sound especially with my family and extended family siting on it for the next few months. We samoans aren't exactly light😉.

How long can plywood span before it bows/ deflects with weight on top? I don't know if I said that right. I've seen some nice looking window seats with underneath storage yet the spacing between supports on them, from one support to another seems more then 600mm plus. I could be wrong. With the appropriate right timber, usually 90x45 I can understand but plywood? I'm no cabinet maker but what am I missing here. I'm guessing thicker plywood as apposed to the standard 18mm used for cabs? If so what size? 32mm over kill? would that be for overall construction of the unit? Is there a way, which I'm sure there is, to determine how far your supports/uprights should be placed for the appropriate material used before deflection/bowing. Appreciate any info

Once again thanks crew!

Just to give an example of what I'm referring to

Screenshot_20200929_112220_com.duckduckgo.mobile.android.jpg what I'm hoping to achieve as opposed to the usually
...
Screenshot_20200929_112042_com.duckduckgo.mobile.android.jpg built plenty of these.

Screenshot_20200929_112237_com.duckduckgo.mobile.android.jpgScreenshot_20200929_112339_com.duckduckgo.mobile.android.jpg

Just a few more examples of what I'm referring to..

TIA

One solution that I would be looking at would be a torsion box, basically two sheets of ply separated by a honeycomb array of supports and structural edging. That way you get the support of a thick solid piece of timber without the weight, and can use thinner, more normally available sheet material.

Works on similar principal to a structural I beam, where you have top and bottom rails separated by a web. When loaded, one rail has to stretch and the other has to compress. The web in the middle is in compression because it is maintaining the separation between the rails. The further the rails are apart, the stronger the beam is for a given rail size or weight. A torsion box is fundamentally an array of interlocking I beams so close together that the rails become a continuous surface top and bottom.

It seems like you want to include drawers or or some other form of storage under the top of the unit, so it becomes an exercise in juggling how wide you need to keep the drawers etc to meet the storage objectives versus how closely you can space the supports dividing the cabinet to support the top. Obviously the wider the span between the supporting uprights, the stronger the top needs to be to minimise deflection, which implies more webbing inside the torsion box, and possibly thicker skins. It is also helpful to arrange the webbing layout so that webs are located above the dividers/supports in the base of the cabinet.

I suspect that 8mm top and bottom sheets and 12mm webbing arranged every 150 to 200mm along and across the torsion box would be adequate provided that webbing joinery is well fitted.

The torsion box needs to be assembled on a flat surface, if there is a bow or warp to the assembly surface, the torsion box will adopt the same defects, and should be virtually impossible to straighten once assembled.

Hope this helps.

Originally Posted by malb

One solution that I would be looking at would be a torsion box, basically two sheets of ply separated by a honeycomb array of supports and structural edging. That way you get the support of a thick solid piece of timber without the weight, and can use thinner, more normally available sheet material.

Works on similar principal to a structural I beam, where you have top and bottom rails separated by a web. When loaded, one rail has to stretch and the other has to compress. The web in the middle is in compression because it is maintaining the separation between the rails. The further the rails are apart, the stronger the beam is for a given rail size or weight. A torsion box is fundamentally an array of interlocking I beams so close together that the rails become a continuous surface top and bottom.

It seems like you want to include drawers or or some other form of storage under the top of the unit, so it becomes an exercise in juggling how wide you need to keep the drawers etc to meet the storage objectives versus how closely you can space the supports dividing the cabinet to support the top. Obviously the wider the span between the supporting uprights, the stronger the top needs to be to minimise deflection, which implies more webbing inside the torsion box, and possibly thicker skins. It is also helpful to arrange the webbing layout so that webs are located above the dividers/supports in the base of the cabinet.

I suspect that 8mm top and bottom sheets and 12mm webbing arranged every 150 to 200mm along and across the torsion box would be adequate provided that webbing joinery is well fitted.

The torsion box needs to be assembled on a flat surface, if there is a bow or warp to the assembly surface, the torsion box will adopt the same defects, and should be virtually impossible to straighten once assembled.

Hope this helps.

Thanks Malb. So the torsion box is constructed Into the horizontal member ABOVE the supports? Where does the torsion box sit in relation to the window seat? I understand where your coming from but not quite sure how it is constructed in relation to the seat. Many thanks for the pointers.

Gonna have to over engineer that one to cater for my family's cheek sizes which have been totally over engineered thru the years from excessive consumption of everything and anything.

I think I follow you now. I thought you meant make the uprights similar to that of how you'd construct the floor of a dble storey with I joist beams. But your referring to torsion sits above the uprights so to span the distances between. I hope I'm right.. LOL

Yeah, the torsion box is the upper surface of the window box. It sits on a framed up carcass with full height dividers between the drawers/storage areas. The carcass would normally sit on a kicker frame to elevate it off the floor so you don't ruffle carpet or scratch a polished floor when accessing the storage areas. Carcass construction can be fairly generic but you want a solid back to lock the dividers into place and stop them racking and some L profile supports across the the front of the storage bays to tie the dividers together there and provide something for drawer fronts/doors to close against. The L profile sections can be as simple as two strips of 50mm carcass material glued at right angles, one sitting horizontal to carry the load from the top, and the other standing vertically to provide some support for the first and something for drawer front/door to close against.

Cool thanks for the clarification malb.

Any reason you can just make individual melamine boxes and clad them. Looks like thats all they have done. We have a similar setup for our "mud room" as per this thread.

Each box has 4 of its own adjustable feet and are then screwed together. You can then have these as drawers or just standard cupboards. The feet are normall hidden by a toe/kick board.

You can then clad the outside with what ever you want to match in, we used the same blackbutt tongue and groove floor boards. But the 16mm melamine carcass will be MORE then strong enough to hold the weight. Also any kitchen mob can make them pretty dam cheap (or do it your self) as thats all they really are, short kitchen cabinets.

What he said ^^^
Basically you either have your supports closer together and a thinner top (16mm) or open the spacing up and use a heavier ( 25 or 32mm) top. Really depends on the look you are after and how big you would like the doors/ drawers underneath

Originally Posted by havabeer69

Any reason you can just make individual melamine boxes and clad them. Looks like thats all they have done. We have a similar setup for our "mud room" as per this thread.

Each box has 4 of its own adjustable feet and are then screwed together. You can then have these as drawers or just standard cupboards. The feet are normall hidden by a toe/kick board.

You can then clad the outside with what ever you want to match in, we used the same blackbutt tongue and groove floor boards. But the 16mm melamine carcass will be MORE then strong enough to hold the weight. Also any kitchen mob can make them pretty dam cheap (or do it your self) as thats all they really are, short kitchen cabinets.

Hey mate. That is exactly what I am after yet I'm not quite sold on sitting on bare18mm carcass cabinets. I'm just not sure whether it would hold up in an environment of let's say rugby players on it. When my side of the family come over you can almost hear all chairs in our household crying when they walk in. Also I wanted to know if there were a way to determine the span let's say plywood before deflection. How far to place uprights. The idea of the torsion box suggest above is one I am considering atm and is a good one.

Usually for work we've built window seats by framing it out during framing stage. The ones where cabs have been used for the window seats our cabinet makers fit Nd install those so I wouldn't know what's or how they make those and I've never spoke to any of them in regards to what I'm asking cause after framing I'm out of there.

I suppose framing it would be fine, but it really does depend what you want underneath?

The melamine boxes arent just 16mm, its then covered with 19mm. So you're now at 35mm and helping to spread that load over a wider area (think of kitchen cabinets with a bench top and how much weight that could take). If you are after a bit more strength you can use ply. I wouldnt have them spaced any further then 600mm wide. Just depends how wide the seat is.

Hey mate.

Originally Posted by havabeer69

I suppose framing it would be fine, but it really does depend what you want underneath?

As per my first post. Window seats I'm hoping to achieve are pictured above. They're the storage units with slide in shelving. Not the ones with the lid on top. Similar to decking seats with storage lids. Those would be no issue as we do those for work.

Originally Posted by havabeer69

The melamine boxes arent just 16mm, its then covered with 19mm.

Dont know if I was clear in my first post but I'm constructing out of plywood. Birch. More structural sound then melamime. Not really a fan of melamime when it comes to carcasses. I was considering framing the whole bloody thing but...

Originally Posted by havabeer69

I wouldnt have them spaced any further then 600mm wide. Just depends how wide the seat is.

I totally agree with that statement yet I'm hoping to achieve a span of no less then 700mm no more than 800mm. Why? It's a trade off. I get myself a new panel saw. My missus gets herself a window seat. I've got another thread asking for assistance with what panel saw to get. And she's gone and picked one I've never done before. I've seen a few at the shops but since covid they aren't open and I can't do the sneakies and see how their constructed and is why I've asked in here forum. You see a few examples online but none with how they're constructed.
Another way was by halfing the depth in half and framing out the section near the wall and the half to the front gets cabs installed yet you only get half depth cabs. Tht breaks that span therefore much stronger then normal cabs used for window seats. Well the ones I've seen. I may go that way but if I do I may not be able to push for a good dust extraction if I don't keep to her brief. . For that she's asked for a specific W. I. R for her AND my daughter.
The torsion box mentioned above is a good idea which Im considering. Spoke to an old mate from previous work and he pretty much stated marbs a bloody f%&$@n genius

.....
The thicker the torsion box, the stronger it will be–by a lot! If you increase a torsion box’s
thickness by 25%, for example, it will be 100% stronger. If you doubled the thickness, it
would be eight times stronger. Strength increases by the thickness cubed.
....

Sorry for the essay figured I'd clarify things. Gotta cut this short, I can hear them stubbies calling my name.

Thanks mate for the assistance.


Edit: I'm assuming this will work. I've not made one like this before. Kinda hoping a cabinet maker would clarify how those window seats with a longer span is created. But I'm thinking I'm going with malbs idea of the torsion box incorporated into the seat.

Originally Posted by Beardy

What he said ^^^
Basically you either have your supports closer together and a thinner top (16mm) or open the spacing up and use a heavier ( 25 or 32mm) top. Really depends on the look you are after and how big you would like the doors/ drawers underneath

Must have missed this while I was typing.. Agreed. I was going with a 32mm ply or simply a hardwood top. Figured I'd have a look at malbs idea of a torsion box with 32mm uprights. Depth of the seats between 500-600mm. Not sure yet as thats huge. Gonna sketch it up and see how it goes..

Length =2600
Depth=500-600
3 cabs spaced at rough 800

Gonna de the math and see. Just been too busy looking at panel saws..

Truly appreciate the advice and the time effort you all take to assist me with my issue. Appreciate it