Cabinet Side-to-Bottom Joint Design
From contributor F:
I've thought about this too and my instinct is to stick with verticals. My reasoning is that the strongest support is the one continuous vertical, whereas if you sandwiched the vertical you could have compression of the top and bottom from the weight of heavier (granite, solid surface) c-tops. Granted it likely wouldn't be all that much depending on the construction material itself.
The horizontals running between the two sides actually carry little if any weight as they just flex until the weight hits the verticals anyway. Also I find it cleaner to have a vertical to attach a finished panel to. Otherwise you have endgrain top and bottom edges you have to deal with. And lastly I think it just looks right, if you see a box built the other way something just seems off. That's just the way I look at it though, so if you think it's worth a shot go for it.
From the original questioner:
Thanks for the response. I used to dado everything, but switched to butt joints several years ago. I have not had any problems. For me, the extra machining wouldn't be worth it. Really, it's only the finished ends I'm concerned with. All my unfinished ends (verticals) get direct support under them, but the finished end hangs out there a little, with the support setting back from the vertical unfinished end (inside the finished end) about 1". Maybe it's nothing to worry about.
From contributor G:
Build a 36" box and see how much dead weight it takes to start deflecting the bottom, a lot more than you think, the screws are working in shear not compression. Also remember you are hopefully using a 3/4" ply rough top which will also help to tie the box system together, add to that a 1/2" back also screwed on and you have a strong box. Granite weight spread out over the total box run is not as heavy a load per square inch as you think. We have built butt joint boxes for kitchens with 3" concrete tops with no problems. Don't overthink your system.
From contributor U:
I have been constructing our boxes like you described for the past four years. We used dado joints before. Switching to this method cut our assembly time drastically. We use 1/4" skins or applied panels on exposed ends and set the toekick back about 1 1/2". We use the same method for the overhead cabinets.
Changing to this method of box construction along with using pocket screws to fasten face frames onto the box is the best improvement I have made in 22 years of business. By the way, I got the idea for this method from this site about four years ago. Not sure who posted it, but I am truly thankful for the idea.
From the original questioner:
Is the method of construction you are using with the bottoms running long and sides on top? What advantages do you feel this gives you? What about uppers where the weight of the cabinet will be downward on the screws, maybe not as good an idea as compared to shear strength? Or are you saying that you just adopted the idea of a butt joint with bottom between sides rather than a dado? Appreciate all the thoughts.
From contributor B:
Bottoms are full length with sides on top. I have had no problems with strength failure on base or overhead. We use a 1/2" construction stapler to fasten sides to bottom and then use 2" screws for extra holding power. The time saved of not cutting dado joints and not listening to a table saw or router doing the dado's is the main advantage. We can have half of the boxes assembled in the time it would take to cut the dado's.
I can figure cabinet part sizes a lot easier this way also. Example: 36" base cabinet with both ends finished will take a 35 1/2" bottom. 1/4" skins applied to both ends. I'm not saying this way is perfect. I have assembled boxes with dowels, with biscuits, and with dado's. They all work! This way seems to fit our shop the best. If anyone else has another idea, I would be glad to hear it. I will try anything if it will help improve time, quality, and profit.
From contributor M:
I construct like contributor B, letting the bottom go full length and the ends rest on the bottom. I also rabbit the bottoms where the ends intersect so I not only get a wood-to-wood joint for easy gluing, but I only have to use staples from the bottom for attachment - no screws. This practice also subtracts from the brain work in a job, since it means the bottoms are cut the exact same length as the cabinet (I do frameless).
I don't really understand the argument for butt joint versus dado construction. Besides giving you a glue-able joint which won't squeeze out glue when compressed like butts do, the dadoes allow you to quickly locate and hold parts in the right location when assembling. I can dado a whole kitchen's worth of parts in about an hour (including the dado for the captive back panels), and I'm sure that those dadoes make the assembly time at least several times that much quicker.
From the original questioner:
Thanks for thoughts guys. This could save me time in assembling cabinets with two finished ends. I pre-finish my face frames and finished ends. Often with two finished ends I have to fuss with the length of the bottom a little because of the variance in thickness of the plywood or doors that are applied on the ends. If I don't have to figure the un-finished ends as part of the equation It would make it easier. I use a faceframe with 1/2" plant on backs that are stapled and screwed on, so the screws on the bottom probably wouldn't matter for downward strength.
From contributor V:
In my first years of furniture and cabinetmaking I had learned to always sandwich the bottom and top shelves between the vertical sides. I make face framed cabinets and I changed my methodology years ago. For me it makes the whole process much easier to have the bottom/top shelves run all the way through. Done like this, the end panels and the interior partitions are both the same height. It eliminates the necessity to take actual panel thickness into account and the length of the bottom/top shelf is the net length of the carcase.
Even on a wall hanging cabinet I feel that my doweled face frame and the cabinet back more than make up for the fact the bottom shelf is pushing against the screw heads instead of being "in shear". I also reason that for interior partitions this has always been the case for those of us that build cabinets as long as possible as opposed to modular boxes. This is only for blind end cabinets. On finished ends I dado the top and/or bottom shelves into the finished ends.
My latest technique for finished ends is to make that end like a blind end with a panel on top of the bottom shelf and then nest the finished end against it only fastened with glue to the back of the faceframe and glue and staples/screws to the cabinet back. This makes the cabinet a bit heavier but saves the time of dado work.
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