Oak bookcases - dominoes or connectors

[mazdaq100]

I have 4 oak bookcases to build for a customer, although I don't think work will start on these for another couple of weeks. I'm in two minds how to build these and looking for some advice. They're all quite big:

2.7 x 1.2m - 2 of these
2.0 x 0.9m
2.3 x 2.15m

No backs to any of them (customer request) but I will fix them to the wall through battens situated at the top of the units and probably halfway down. Maybe some L-brackets too.

The only one I could fit in my van assembled is the 2.0 x 0.9m one. The others would need to be assembled on site or I hire a bigger van to transport them. So I'm thinking of building all of them with the KV connectors and assembling all on site with no glue (2 connectors per shelf and a domino in the middle). I've done this before for some birch plywood units of this size and got a good result - these will be my first ones from oak however. I am starting to now think more in terms of what looks best for the customer and weighing up the pros and cons:

The upside of the connectors is they'll make transport easy and less stressful assembly on site - no glue and no clamping required. The downside is some of the connectors will be visible although I can "hide" many of them on the bottom of the shelves and top of the shelves for the higher ones.

Alternative is I just use exclusively dominoes but then I have the stress of gluing up on site and clamping, or I assemble at home and rent a bigger van to deliver them to client. I will almost certainly need to hire someone to help me shift these too, eating into the bottom line. Plus I'm worried about glue smear at the joints showing through the clear oil if I went for a glued assembly with dominoes.

I've done a few of these units in the past with connectors and never had any comeback from customers about the look of the connectors. Maybe I am overthinking the whole thing but interested in other opinions.

 

[Packard]

According to Google A.I., use the connectors for positioning and clamping only. Add regular dominoes and glue to carry the load.

Festool has stated that the
Domino connectors are not designed for load in isolation. They are intended for alignment and clamping force, with the strength of the joint primarily coming from the adjacent glued-in standard Dominos and the wood itself. The final weight capacity of a joint depends heavily on the specific application, the type and quality of wood used, and the overall design of the project.

I would dry fit everything before going to the site. Bring a drop cloth, glue and all the required dominoes and connectors. A couple of bar clamps, and a rubber mallet may also make sense as the glue can turn dowels, and presumably dominoes, into little hydraulic springs. Once fully in place, I would expect that the connectors would be sufficient until the glue dries.

I would do this in 2 trips. First trip: Assemble and glue. Second trip (24 hours later) install after glue dries.

Note: I am a dowel guy. Someone with Domino experience may want to amend the above. But the Festool quote from Google A.I. is solid information.

 

[rmhinden]

IMHO, rent a bigger van (or movers). That way you can assembly them in your shop where you have room, benches, clamps, tools, etc. Then just transport them to your customer and install.

Bob

 

[cpw]

I would at least have two dominos outboard per shelf. The dominos can bear the weight. With just one, I would worry about the single domino having something heavy potentially act as a lever on it.

 

[mazdaq100]

I would at least have two dominos outboard per shelf. The dominos can bear the weight. With just one, I would worry about the single domino having something heavy potentially act as a lever on it.

Interesting you should say that as have been using ChatGPT to help plan these this evening and their recommendation was for one KD connector at the front then 2 dominoes, one on tight setting and glued in place and the other on the medium-wide setting, which would be dry fit to allow for movement of the oak across the depth of the board.

As you say, 2 dominoes will bear the load along with glue around the tight domino. Then I can use the KD connector to act as a clamp while I assemble on site along with a few bar clamps on the back side of the unit, nearest the dry fit domino. Should be minimal glue squeeze out if I'm only gluing the one domino.

I could apply the finish beforehand in my workshop too, leaving minimal time on site.

Hopefully a solid plan but interested to hear any other thoughts. I certainly value members' opinions on here more highly than ChatGPT (although it has helped me successfully figuring out various issues recently!!)

 

[luvmytoolz]

I wouldn't worry about doing a wide slot, the grain on the boards will all be going the same way so any expansion or contraction will be uniform.

As an avid book lover household we tend to stack our bookcases pretty heavily, You don't say how deep they are but if it's deep enough I'd go 2 connectors and 2 tenons on tight setting or at least 2 connectors and one tenon. and seeing as you're fixing it to the wall, you wouldn't really need to glue, although I would prefer to glue it myself.

Any vertical divider/supports you put in will also greatly help with strength.

 

[4nthony]

I would at least have two dominos outboard per shelf. The dominos can bear the weight. With just one, I would worry about the single domino having something heavy potentially act as a lever on it.

I agree with this. I used Domino connectors on a recent project and for the most part, I put a domino next to each connector to act as support.

In this photo, I extended a desk off the side of the bed/dresser and paired 3 dominos with 2 connectors.

 

[ChuckS]

AI is a great tool for a lot of things, including tackling technical concerns in woodworking. But it doesn't experiment and learn from it like a hands-on woodworker does -- yet. You can use scraps with some connectors and dominoes to do a sample joint or joints to study your concerrn. The exercise itself is particularly insightful if this is the first time you use the knock-down kit.

The instructions given by Festool, which AI most likely relies on, is a general recommnedation based on its in-house tests. On more than one occasion, I did my domino projects while ignoring some given guidelines found in the domino user guide or manual.

 

[Packard]

The connectors will only be stressed in shear for the shelves.

I have been examining images of the connectors.

Here’s one:

https://media.cdn.festool.io/productmedia/Images/jpg_large/fe81c67d-6c20-11e5-80d2-005056b31774_1600_1200.webp

If:

The metal stud running through the connector is steel.
If the stud is of one piece through the molded part

Then:

The weakest link will be the wood into which the connector is placed.

Note: I don’t have any sample connectors to measure, but a 3/16” diameter rod had about 40,000 pounds per square inch shear strength, then about 1,1,00 pounds per fastener.

I made assumptions: First that the stud is mild steel. Second that the minimum diameter is 0.187”. But is shear it should be quite strong. Below is the best image I could find showing shear force. But don’t ask me to distinguish between negative and positive shear force.

 

[Cheese]

It may also help to understand how heavily loaded the client plans to load the shelves along with noting the depth of the shelves. The anticipated load and depth of the shelves also contributes to choosing the correct material and construction for the shelves. Most of the book shelves I'm familiar with are about 30" wide/long and 12"-18" deep.

I'd follow the @4nthony suggestion/placement using 3 Dominos and 2 connectors. A single connector used with 2 Dominos will not pull the carcass together properly, it will want to rack.

 

[mazdaq100]

Thanks all. The depth of the shelf is 244mm. I'm thinking 3 dominoes with 2 connectors may be overkill. 2 of each should be sufficient.

I'll be putting dividers on each shelf - not in one vertical line but alternating from one side to the other. Regarding load, I believe the plan is to have it fairly loaded with books but some compartments will be left open with just a plant/ornament in it.

 

[Cheese]

Thanks all. The depth of the shelf is 244mm. I'm thinking 3 dominoes with 2 connectors may be overkill. 2 of each should be sufficient.

I'll be putting dividers on each shelf - not in one vertical line but alternating from one side to the other. Regarding load, I believe the plan is to have it fairly loaded with books but some compartments will be left open with just a plant/ornament in it.

With a depth of only 244mm, you'll not need 3 Dominos. Shelves that are only 9.5" deep make a lot of the structural decisions easier.

 

[smorgasbord]

The Domino Product Manager likes to use lots of dominos and connectors. Here's a shot from his bed making video:


There are many ways to skin this cat. The EnCurtis YouTuber talked about doing a housed domino joint here:

 

[Packard]

The kitchen cabinet trade association contracted an outside engineering firm to compare a variety of fasteners.

I am not going to go into the comparison now, but they universally recommended that no fasteners should be used within 2” of the edge of any board. The reason is that the board tends to fail if the fastener is not surrounded by sufficient board spade.

So in Smorgasbord’s image above, I am in favor an abundance of fasteners, but would have spaced the two outermost fasteners further from the edge of the board. I think that would necessitate the fasteners to be:

Connector—-Domino—-Domino—-Domino—-Connector.

I would note that while a dado (like in the housed domino joint) adds substantial shelf load carrying capacity, the dado itself, even when very tightly fitted, added no measurable racking strength to the joint. The Dominos would. Have to provide all the racking strength in a substantially shallower inset.

So if shelf joint is to contribute to the racking strength of the shelf cabinet, the housed joint might not be the best choice.

However, in this case the shelves are going to be mounted to the wall and the wall becomes an integral part of the structure of the shelf unit. So racking will not be an issue. The main advantage of the dado, in my opinion, is that it accurately locates the joint.

When I made shelves with dado joints, I would dado the wide board first then rip the sides to width. That guaranteed that the left side’s dado was exactly the same height as the right side dado (without me having to use a ruler).

 

[smorgasbord]

no fasteners should be used within 2” of the edge of any board... Connector—-Domino—-Domino—-Domino—-Connector.

(sorry, hit Save accidentally too soon)

With a 9.5" board, you're losing 4", so putting 5 "things" into 5.5" seems pretty tight. Maybe just 2 of each, and maybe:

Front of Unit -- Connector -- Domino -- Connector -- Domino -- Back of Unit

I think some of what I'd do depended on how the unit is attached to the wall. Given it doesn't have an attached back, I'd be careful about what's supporting what.

So, first thing is I'd make the bottom the full width, with the vertical sides resting on top of it. That way, at least, you could attach the bottom to the wall and it would support the bookcase in compression, rather than tension. Tension would rely on the connectors/glued dominos, and I think it's better to have mechanical support.

But, you're also going to want to attach the top and/or the sides as well so that the bookcase doesn't fall forward. L-brackets are ugly unless they're hidden somehow.

 

[Crazyraceguy]

Without a back, that 2.3 x 2.15 is going to be quite a thing to handle alone. A back would add considerably to the racking issue, while handling. It might even be a bit of a problem to navigate through doorways. Mabe give a bit more thought to assembling that one on site? A back would also go a long way in supporting such wide shelves.
I single vertical divider, in the middle, would still leave effective width of over 1M. I didn't see anything about the thickness of these shelves? So, unless I missed it somewhere, there could be a sagging problem.

 

[MacBoy]

If you are moving it assembled from your place to the Client’s place, then put on a temporary back, or diagonal strips on the back.

That will give you lots more stability for the move, and also way less stress.

 

[smorgasbord]

Isn't the whole point of using the connectors so that it can be assembled on site?

 

[mazdaq100]

Isn't the whole point of using the connectors so that it can be assembled on site?

That was my thinking, which is why I was planning to use them due to the size of these units. I think I'm settled on 2 connectors (for clamping pressure) and 2 dominoes (3 seems too much on a piece 244mm wide). Plan to use 8x40 dominoes so I don't have to keep changing the bit between a 6 and an 8. I will glue the dominoes into the mortices of the shelves (25mm deep) and then have a 15mm mortice in the uprights. It's 18mm thick oak so only leaves 3mm in the uprights but I think that should be ok? Could always switch to 12 and 28mm.

Would you guys glue the dominoes into the upright mortices or leave them dry? To be able to disassemble in the future, should leave them dry obviously although the client hasn't requested that. I'm just wondering how much extra stress gluing up will add when assembling on site and whether it will make that much of a difference.

 

[mazdaq100]

Without a back, that 2.3 x 2.15 is going to be quite a thing to handle alone. A back would add considerably to the racking issue, while handling. It might even be a bit of a problem to navigate through doorways. Mabe give a bit more thought to assembling that one on site? A back would also go a long way in supporting such wide shelves.
I single vertical divider, in the middle, would still leave effective width of over 1M. I didn't see anything about the thickness of these shelves? So, unless I missed it somewhere, there could be a sagging problem.

18mm thick oak. Regarding the dividers in the 2.3 x 2.15m unit I'm planning an alternating pattern of 2-1-2-1 over 7 shelves so although there will be a span of just over 1m on alternate shelves, the 2 dividers below will support that span. I did use the sagulator while planning these and all sag is well within the "acceptable" range.