Hi there. Planning out a custom built-in for my living room, had a quick question regarding cabinet box best practices. Hoping someone here might have some insights.
To provide some context, the built in base will be 3 cabinets on a 2×4 ladder. The two outside cabs will be 27 3/8 w x 27″ h x 24″ d (incl face). The mid cab will be 54 3/4″ w, same H and D. Cab will be 3/4″ hardwood ply, with dados and rabbets + titebond + cab screws for assembly (no screws on exposed side). A 6/4 maple top will cover it, with a 6/4 maple bookcase on the back of the top (against the wall). Bookcase will have 5 verts, max unloaded weight on cabs will be 470 lbs, with books (~20lbs / linear ft = 640lbs) the max estimated weight on cabs ~1100lbs.
(fyi, I used https://www.inchcalculator.com/lumber-weight-calculator/ to get the max weights with maple).
Okay, so here are my questions:
1) That’s a lot of weight… and doesn’t include anything inside the actual cabs. Is it too much for well constructed 3/4 ply base cabinets? Note that both the cabs and the bookcase will be secured to studs on the left side and back (it’s in a corner), and the ply walls will be doubled between the cabs (screwed directly together, no space).
2) I plan to dado the cab bottom into the sides and back, rabbet the cab back into the sides (hide the edges), and butt joint two 3″ top strips to the sides (front and back). Do I need to be more aggressive with the strips? Rabbeting the strips into the sides seems like overkill (and might compromise the sides?), but I could rabbet the back strip onto the cab back?
3) Is there any kind of rule for rabbets on a cabinet? In other words, should horizontal pieces always be rabbeted onto vertical pieces (i.e., material removed from horizontals, verticals shortened to accommodate lip)? Vice versa? I can’t find anything telling me whether this matters…
4) Side note, am I insane for using 6/4 for the bookcase shelves? I like thicker shelves, and using 6/4 (same as the verts) seemed both stronger (books) and easier (than building 12 12″ x 1.5″ boxes). That said, my spans are only 27″, and the 6/4 probably doubles the potential weight of the shelves. (fyi, shelves will be either dado or stopped dado into the verts).
Sorry for how long this post is, but I like to make sure I provide enough detail for an informed response. Appreciate any thoughts.
Thanks,
Rick
Replies
You may have an issue with the long middle shelves even with 6/4
Hey, thx for the response. Not sure I understand the "long middle shelves" reference... do you mean the middle shelves of the bookshelf? Is the concern that the center vertical support is in the middle of the wider base cabinet. Couple thoughts:
- The "counter" on the cabs (under the bookshelf) is also 6/4 and will be three 8" w x 115" l 6/4 maple boards (titebond). My assumption is that that counter will distribute weight fairly uniformly to the cabs.
- None of my bookshelves are longer than 27" (at present), so there aren't really any long shelves....? I can't imagine a scenario where 6/4 hard maple would sag at 27"...?
- The bookshelf vert supports will "mostly" line up with the cab walls, the only exception being that center vertical (middle of wide cab). I say mostly because the cabs will need to be offset from the left wall 1-2" (for cab door if I full overlay and because left wall isn't true).
- My total weight calcs include the counter's weight. Counter weight is about 112lbs (max), or about 10% of the total load. So that's not "on" the counter.
- Those weight calcs are extremes (worst case), and assume heaviest maple and wall to wall books. I don't think I'll come close to those numbers, but like to know what they are. :)
Let me know. Thanks.
-rt
I wrote a longer reply, but the forum seems to have eaten it. Ugh.
Not sure what you mean by "long middle shelves" since none of the bookshelf shelves exceed 27"? Do you mean because the vertical support in the center of the bookshelf isn't directly supported by any cabinet sides? The counter is 6/4 maple... so I'd assume that will largely even out the weight distribution on the cabs, which should have at least a 1500lb load capacity... no?
Interested in any thoughts.
Thanks,
Rick
I assumed the middle cabinet had shelves.
I rarely ever use glue building cab boxes. Definitely face frames, tho.
Ah, makes sense. The center cab will have 3 drawers. One long drawer along the top (for a digital piano) and two side by side narrower/taller drawers at the bottom.
I typically use titebond in all my woodworking unless the work needs to be disassembled in the future. The reason is that - all things being equal - there is no joint as strong as a glued point, and I'd rather over-engineer the joint than under engineer it. With this much weight my feeling is that dado/rabbet joints (max joint surface) with titebond will effectively make the box a continuous structure.
-rt
Thanks for the info I will try to figure it out for more.
aces etm
With that much weight, I would want the vertical members carrying the weight from the top, straight down to the floor. I wouldn't want a weight bearing member sitting in the middle of the lower cabinet.
I hear you. I've designed things so that bookshelf's 1, 2, 4, and 5 verticals will match up with the box sides, which will then match up with the ladder cross-members (2x4). So, for 4 of the bookshelf supports the weight will be directly transferable from the vertical to the box sides to the 2x4 to the floor.
The only exception is the middle bookshelf support (vert 3), which rests on the center of the wide bottom cabinet. However, my thinking is that the:
1) The 6/4 maple countertop (along with the front and back top strips) will distribute that force laterally, allowing that weight to be diffused/distributed to the four cabinet sides and thus to the floor.
2) The bookcase will be 12" off the wall in the back of the cabinet. In that position most of the weight will actually be put on the cabinet back, which is 3/4 ply rabbeted and glues into the sides. The cabinet back also sits entirely on the ladder 2x4 that stretches along the wall.
3) The sides of the wide cabinet will actually be double thickness since they'll be married to the sides of the smaller cabinets. That means the center cabinet will have 1.5" of ply to carry the load of bookcase verts 2, 3, and 4 (which will probably get most of that center load).
Thoughts? I don't have a lot of practical experience with how counters distribute force to the cabinets they sit on, which is my one concern... I just don't know how thick a counter needs to be to distribute forces appropriately (or how to calculate it).
Thanks,
Rick
I've designed things so that bookshelf verticals 1, 2, 4, and 5 match up with the box sides, which then match up with the ladder cross-members (2x4). So, for 4 of the bookshelf supports the weight will be directly transferred to the floor.
To your comment, the exception is the middle bookshelf support (vert 3). However, my thinking is:
1) The 6/4 maple countertop will largely distribute that force laterally, transferring weight to the four cabinet sides and thus to the floor.
2) The bookcase will be agsinst the wall on the back of the cabinet. So, most of the weight will be on the cabinet back, which is 3/4 ply rabbeted and glued to the sides. The back also sits on the ladder 2x4 that stretches along the wall.
3) The sides of the wide cabinet will be doubled by the smaller cabinets. That means the center cabinet will have 1.5" of ply to carry the load of bookcase verts 2, 3, and 4.
Thoughts? I don't have a lot of experience with how counters distribute force laterally, which is my one concern... I just don't know how thick a counter needs to be to distribute forces appropriately (or how to calculate it). I could always put a top on the center cabinet box (rather than just two strips)...
Thanks,
Rick
I've designed things so that bookshelf verticals 1, 2, 4, and 5 match up with the box sides, which then match up with the ladder cross-members (2x4). So, for 4 of the bookshelf supports the weight will be directly transferred to the floor.
To your comment, the exception is the middle bookshelf support (vert 3). However, my thinking is:
1) The 6/4 maple countertop will largely distribute that force laterally, transferring weight to the four cabinet sides and thus to the floor.
2) The bookcase will be agsinst the wall on the back of the cabinet. So, most of the weight will be on the cabinet back, which is 3/4 ply rabbeted and glued to the sides. The back also sits on the ladder 2x4 that stretches along the wall.
3) The sides of the wide cabinet will be doubled by the smaller cabinets. That means the center cabinet will have 1.5" of ply to carry the load of bookcase verts 2, 3, and 4.
Thoughts? Let me know.
Thanks,
Rick
On the shelves, I have made several editions of book shelves using 3/4 ply with 1 1/2" deep edging front and back. Same look and stiffness as stock with less weight and cost. Also the thickened edge hides the pins if the book shelves will be adjustable
Great point. Yeah, I've made similar shelving for all our closets, including in the built-ins I made for the kids closets. I typically use 3/4 hard ply with 2-3" x 3/4" hardwood glued and nailed to the front edge.
It generally works fine for shelves, especially if the load is lower. However, it's nowhere near as strong as a solid piece of 6/4.
https://www.popularwoodworking.com/projects/aw-extra-3614-stronger-shelves/
Not that I need 6/4 strength at 27", but I KNOW it won't bow, even with a block of lead on the shelf. :)
At the same time, I also like the look of a solid "box" more than the L of the front-edged approach. In a close the L works fine, but in my living room I really want the clean lines of a solid box. So, it's either 6/4 or I build a box for each shelf.
-rt
There is a reason most cabinets are built from 3/4 inch stock - it works.
Wood is phenomenally strong in compression so you don't need to overthink the weight - just make sure the floor is going to be strong enough.
Spans of 27" will be fine.
In terms of distributing the weight from above, you have to think about the lowest cross-member that will be supporting any weight as being the 'floor' for the weight above. If you would be happy building the rest of your unit on top of it, were it the floor, then it is strong enough. If not, then reinforce it. TBH I think this is a bit 'built on the Clyde' and is way, way stronger than it needs to be for the described loads.
Would it be an option to use birch ply for internals? It weighs a lot less than hardwood ply, though is often a little more expensive. It is also easier to work with, less splintery and easier on the lungs. Edge-band it with show timber or cover with a face frame.
Yes, you are bonkers using 6/4 stock for shelves. It's way too heavy, will be awkward to work with and will look very thick. Also when it moves it will drag everything with it. If that's the look you want, I suggest using 3/4 inch shelves with a 11/2 inch thick lip. It'll be cheaper too. If you are worried about bowing (you should not be unless your books are made of concrete) then add a supporting pin into the wall behind the unit. If you are really paranoid, a half inch batten will also do the job, and then you could probably load it with bricks.
The only structural concern I would have is the free end panel - a dado may not be strong enough to prevent bowing and failure so you might prefer to use screws and plugs there, even though you hate the idea (admit it, you do...) It will not likely be a problem, but you asked about best-practice. Dados are great for supporting shelves but don't hold sides on well and do not resist racking. There is insufficient glue area for a strong joint so they are best used where there is good support from a back to prevent bowing.
An alternative might be to use dominos to re-inforce the dado joint or to use 1/2 inch ply and screws then bond a 1/4 inch sheet over it for perfection. That having been said, if you fix the shelving to the wall as you should, the studs will take most of the weight anyway. You have the additional benefit of the corner, which will help keep things lined up nicely too.
If you are going to fix the free edge to the wall then there is no issue. The wall will act like the back of a cabinet and prevent dado failure.
I linked this in another post today, but it is highly relevant to your question to: https://www.youtube.com/watch?v=NX6FBYHyLrw
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Wow, awesome response, thx for all the feedback and thoughts. Video was great, if only I had a 1500 foot work room with 45 clamps and a 10x10 table saw, lol. Gonna have to reply in stages to get all this in...
"In terms of distributing the weight from above..."
Never heard the term "built on the Clyde", will remember that. :) My philosophy is similar to the guys who built my Lasko fan in the '70s, which has run almost continuously since 1987. Someone may stand on the cabinet, multiple folks may sit on it, whatever... if it fails it would be catastrophic, and that's not acceptable, even if the odds are small.
So, it sounds like you think the load will all transfer through to the ladder 2x4s / floor itself, which is more than fine? My actual floors are wood on concrete (single story ranch, slab on grade). The wood is engineered, essentially horizontal textured plywood, so I assume it should be fine with pretty extreme loads on it?
Indeed, your load will be more than adequately catered for. I am sure an engineer could calculate the weight required to fracture your slab, but even your plan to pile half a deciduous forest on top of it is unlikely to cause it any harm ;-)
Seriously - this is way stronger than it needs to be for anything you described - the cabinets built in the video I linked would easily meet your requirements. What you are doing will certainly work. No doubt about it. It will be solid and safe. It will also look heavy and cost a fair bit more than it needs to. Still in the end it's your unit, and if you love it then it's fine - don't worry about it falling over - in an earthquake, it may be the thing that keeps your house standing!
"Would it be an option to use birch ply for internals?"
Uhh... sure? Isn't birch a hardwood plywood? Birch is a hardwood... afaik hardwood ply is just ply made with a hardwood veneer? Quality and strength are generally factors of the number of plys and how the plys are assembled... e.g., Chinese plys are maybe 5 ply with poor manufacturing and voids, domestic ply may be 7 or more with fewer voids, etc.
Maybe I'm missing something or what you mean by "internals"?
Yes, Birch is a hardwood, but there is a 'brown hardwood' grade of ply which has much higher density and an awful propensity to splinter. Species varies. I have not weighed the sheets but estimate at least 40% heavier for the 'hardwood ply'
Internals = bits you can't see when the doors are shut!
"Built on the Clyde" - a term used in Northern England to describe a person of very large size, after the great shipyards where once massive vessels were constructed by hefty machinery.
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"Yes, you are bonkers using 6/4 stock for shelves"
Haha, yeah... I know. The shelves would/will be 250+ lbs, so just getting them up has me sweating.
Basically I like the look of "thicker" rather than "lipped" shelves (face frame on 3/4"). On an eye level bookshelf the difference is obvious, and to me lipped shelves look cheaper. So, I really want squared boxes. My thinking is that:
1) 6/4 material cost isn't much higher ($100-$200 max), and eliminates most of the work/time involved making 12 shelf boxes and 5 corresponding "thick" vertical supports
2) 6/4 is mountains stronger than a face framed 3/4 ply (which I've used in all our closets). Like, 50%+ stronger. Over-engineered maybe, but it's also future proof.
The bookshelf itself will be secured to studs at the top (L brackets above the top shelf and behind moulding) and the counter from below (inside the cabinet).
Well that will work, and if it is well acclimated to your environment that 6/4 stock might not pull the whole thing apart.
As you say, it will be stronger, but it will be stronger in much the same way that a Hummer is 'stronger' than an Aston Martin DB8 - Both will get you from A to B in reasonable comfort, but one is a lot more efficient than the other. If you want the 6/4 thick look then I agree, it makes sense to do it that way, but if you want that much strength, and the look is the result then it is simply not needed.
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"The only structural concern I would have is the free end panel"
*sigh*, it's a good point. I think the bottom panel dado + the back rabbet will be strong, and I plan to lag bolt the entire back of the cab to the studs behind it, but maybe that's not enough to hold that end together?
I may actually want some decorative framing on that end, in which case I could just face it with some 1/4 material (similar to what the guy did in the video you shared). That wouldn't be the end of the world, and it would allow me to really secure that face (beyond the glue and
One question is if pocket screws would suffice (versus screwing in the panel from the open side). They won't have the same strength, but do they need to be THAT strong? I could pocket the bottom to the side from the under side and the back to the side from behind. Both are 3/4", which would seem to be sufficient?
With all the support you will get from the back, there is no need for concern about the free end panel.
These fail only when they have an opportunity to bow or rack, which will not be an issue here.
Yes, you could use pocket screws but with only 18mm or less for holding, will not add significantly to the strength over and above glue.
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