how much to glue with Domino cabinet construction.

[RAW]

Hello FOG group. Newbie here with a question.
I am about to build a set of mudroom cabinets with my newly acquired Domino 500. I am also intrigued with using prefinished plywood. My question is with the carcass box standard 24" depth I will use three tenons. Because the plywood is prefinished glue will not work between the tenon joints and I don't want to mask and sand down a strip for glue. Can I assemble the cabinets only using the tenon joints with glue?

 

[tjbnwi]

Use Melamine glue. It sticks to most pre-finished woods.

Tom

 

[ChuckM]

The short answer is yes, with just glue and three tenons. If for a bit of extra holding that you want to use four tenons, you can do that too.

 

[Crazyraceguy]

I would agree with both above, and make the choice based on strength requirements. The glue/tenons alone is plenty strong, but in a particularly stressed joint, Melamine glue does add some strength. You do have to keep in mind though that it is plywood, so the best you are going to get is at the weakest link. You can be 100% stuck to the outer veneer, but if the adhesion to the next layer fails? you are still in a failure.
Also, with Ply, be careful to brush/paddle/stick/whatever the glue around in the mortise. You need good coverage, but that doesn't mean a lot of glue is better. Too much causes hydraulic pressure, which can/will split your plys looking for a way out.

 

[sancho57]

id add some screws to the sides that wont be visable.

which means the sides that are on the out side of the run...

Pocket hole on the top and bottom work real good for this and are not visable

 

[Packard]

I would say that a lot depends on the design of the cabinet. 

Cheap RTA (Ready To Assemble) furniture often use various joiners and no glue.  The RTA cabinets can be quite sturdy, gaining a structural component (the wall). 

Racking, the side to side movement of a cube is greatly mitigated by adding a rear panel. 

So absent of a sketch to show the design, advice will have limited value. 

But basically, tenons, like dowels, impart pull-out strength mainly. It gains racking strength by the thickness of the panel, weather glued or not glued.  The thicker panels act as a fulcrum with the domino anchoring the two edges. 

So, a sketch please.

The RTA (cabinets) and the RTA (furniture) associations both contracted engineering firms to determine which joinery method provides the most rigid construction. 

They joined vertical panel with a horizontal panel using the hardware only (no glue).  The tested.  The loaded the end of the horizontal panel to failure.

1. Cam lock hardware
2. Wood screws (conventional)
3. Confirmat type screws
4. Dowels

The cam lock hardware failed before the scale showed any poundage on the scale. 

Wood screws did marginally better.

Confirmat screws and dowels were in a virtual tie.  They offered the racking strength of dowels with the fact that they did not require glue or clamping.

Dowels could be hidden.  Dowels required glue and clamping.

Dominoes were not tested as they do not lend themselves to high production builds. 

I would imagine that they would fair about the same as dowels and confirmats.

I settled on Confirmats where they would not show and dowels where I wanted hidden fasteners. 

I use 8mm dowels and when I need KD construction, I use Hafele joiners in the 8mm holes.  Glue is a must.  You need to add enough glue that the moisture will swell the dowel (or domino) to add a mechanical component to the strength.

A very light coating of glue will rely on the glue only.

I tested a dowel joint with water only on the dowels (no glue).  Allowed to dry overnight the dowels had swollen enough that I could not pull the joint apart by hand.  A mallet was required.

I imagine that dominoes would be the same.  I have never seen anyone write about testing water-only on dominoes.  It would be interesting.
So th

 

[ChuckM]

About back panels, I assume by OP's reference of carcass box that the cabinets will all have back pieces that resist racking.

 

[Packard]

About back panels, I assume by OP's reference of carcass box that the cabinets will all have back pieces that resist racking.

I think you need more information than that. 

Is the back panel being slid into grooves on the sides only and pinned in position with a couple of nails?

Is the back panel just being “captured” (no nails or glue) in the grooves?

Is it being nailed and glued to a rabbet at the rear?

It is hard to glue a back panel in a groove.  It is easy to glue a back panel into a rabbet at the rear. 

I still say that without more details on the design of the structure, advice is largely guesswork based on how the advisor would have constructed the cube, which may differ significantly from the way the OP plans on making it.

 

[Packard]

I forgot to add about the RTA testing.

Both engineering firms recommended that no fasteners be applied within 2” of the ends of a panel, whether plywood, MDF or particle board. 

Apparently the panel needs that 2” to maintain structure if racking occurs.  I would guess the same would apply to dominoes.

 

[Michael Kellough]

I’d use five Dominos along the 24” joint. Seven if you expect more than normal stress.

 

[ChuckM]

About back panels, I assume by OP's reference of carcass box that the cabinets will all have back pieces that resist racking.

I think you need more information than that. 

Is the back panel being slid into grooves on the sides only and pinned in position with a couple of nails?

Is the back panel just being “captured” (no nails or glue) in the grooves?

Is it being nailed and glued to a rabbet at the rear?

It is hard to glue a back panel in a groove.  It is easy to glue a back panel into a rabbet at the rear. 

I still say that without more details on the design of the structure, advice is largely guesswork based on how the advisor would have constructed the cube, which may differ significantly from the way the OP plans on making it.

While it's true that more details would benefit us in giving our comments, but I'm not doing a PhD dissertation, and I'd simply give what I think is good based on the info. available. If the OP comes forward with more or new info., I can easily adjust or supplement my comments as appropriate.

 

[Packard]

About back panels, I assume by OP's reference of carcass box that the cabinets will all have back pieces that resist racking.

I think you need more information than that. 

Is the back panel being slid into grooves on the sides only and pinned in position with a couple of nails?

Is the back panel just being “captured” (no nails or glue) in the grooves?

Is it being nailed and glued to a rabbet at the rear?

It is hard to glue a back panel in a groove.  It is easy to glue a back panel into a rabbet at the rear. 

I still say that without more details on the design of the structure, advice is largely guesswork based on how the advisor would have constructed the cube, which may differ significantly from the way the OP plans on making it.

While it's true that more details would benefit us in giving our comments, but I'm not doing a PhD dissertation, and I'd simply give what I think is good based on the info. available. If the OP comes forward with more or new info., I can easily adjust or supplement my comments as appropriate.

He does not even say how thick the plywood is. 

I built a book case for the local Starbucks to use as a “lending library”.  That was 12 years ago.  It has taken retail-store-abuse for all that time and only the edgebanding had to be replaced.

I used no fasteners at all in the construction.  The back and the sides had 3/4” x 3/8” grooves for the shelves to fit into and just glue.  It is still as sturdy as the day it was built. 

So, I could design a wobbly cube using 5 dominoes per joint and I could design one using 3 per joint that would be robust. 

The writer said he was new at this, so I would not assume much about the design.

I am not faulting the people who are answering this thread.  They are responding as they would have designed the piece.  How much work is it for the OP to describe the piece in a bit more detail?

 

[RAW]

Thank you for the input, folks. Some are helpful, others a bit abusive. [sad]. So I am very capable of building cabs using non festool tools. ie dado, rabbet glue, and perhaps dowels. I am a retired architect of 32 years, so I do have a design background. My retirement has started with a new lakehouse built and I want to build the cabs myself. There are a lot of them, So I picked up the domino machine, curious about the speed it offered; I own the Conturo edge band with table and accessories kit. I have the MFK trimmer and kit, I also just purchased the OF1400 router with the LR32 rails and accessory kit. So I'm well invested here. I thought it was natural to join in the discussions with FOG, and I really want to learn how to chase the mm in all the work I do and create accurate and well-built furniture. Excuse the drawings, as that was my first mistake. Next time all metric as I picked up the plywood yesterday, and it's not exactly 3/4", So that was an uh-huh moment. To answer questions. I will include a 1/4" backing panel glued into a groove, not dado. The plywood is 18mm (not 19) baltic birch prefinished. My curiosity comes from the idea that if Festool promotes the quick connect system, which is glueless for flat packing projects, then doesn't it stand to reason that the Domino Tennon provides the same structural integrity without having to glue up?

 

[Packard]

My understanding is that Dominoes and dowels primary strength is their ability to resist pull-out.  They are better at that than screws, and they do add some racking strength due to the size of the tenon. 

But if you visualize a 18mm thick panel with the domino in the center, resisting pullout means that racking would have to compress one edge.  That is the reason the thicker panels are stronger. 

My CMT dowel jig, which is not distributed in the USA, but is in the rest of the world, has 8mm dowels spaced 32mm on center. 

With one domino equal to about 3 dowels, the math becomes simple:  1 domino per 96mm (3.78”).  (Keeping in mind that none of the fasteners should be closer to the edge than 2”.)

I am assuming that someone years earlier had determined that 32mm was the optimum spacing for dowel construction.  If that assumption is not correct, then all my calculation are garbage too.

 

[Michael Kellough]

The quick connect fasteners not only “fix” the parts they PULL the parts together gaining leverage from the height (18mm) of the panel. Doesn’t seem like much but without the PULL a simple wood tenon gains zero leverage. Talking about a dry joint here, not glued.

I would not put the back panels in grooves. You can’t really use them to square up the carcass when you cant see how the contact is made with the edge of the thin panel and the bottom of the groove.

Most commercial cabinets just use nailed on panels. Quick and simple way to make the carcase square, as long as you’ve developed the ability to cut your backing panels square.

At installation a pre-finished cover panel is scribed to fit the wall and cover the ugly edge of the backing panel.

 

[Packard]

I also prefer adding the back panel by nailing to a rabbet.  For greater strength, adding glue. 

I was taught that “dadoes” applies to cross grain cuts only; everything else is “grooves” and I use those terms that way here. 

If you use a groove for the back panel, gluing becomes an issue.  If you apply glue to the panels, sliding the panel in will largely wipe the glue off.

If you apply it to the groove, then the panel acts like a piston and forces the glue out of the joint.

Rabbet construction solves the glue issue. 

I use picture framers’ corner clamps to hold the cabinet square during glue-up.  I rarely have to clamp the diagonal to square up case work. 

You do have to check squareness before nailing the rear panel.

I would add that Baltic birch is a higher specification panel than usually used in case work.  It is stronger in all ways and almost always lays perfectly flat.  It is also more expensive.  I use it rarely (because of the expense), and only where I think the added strength is a benefit.

 

[Michael Kellough]

Pre-finished Baltic birch is such a nice assembly of veneers that it increases design options.
It’s so nice I wouldn’t use it for kitchen cabinets either unless you want utilize the pinstripe appearance of a cut edge.

I’d reserve BB for freestanding cabinets and in that case I would house backing panels in a groove to make further use of the pinstripe.

 

[Packard]

I would never use Baltic birch and then paint the cabinets.  And as you said, no edge banding (less work) results in a really nice look.  Never any voids. 

I’ve used grain filler on edges of conventional birch plywood, and while not as nice, it also makes an acceptable look.

My favorite part is that the panels are always flat.  That is not so (especially since the pandemic, during which quality went to the dumps).

 

[RAW]

Thank you folks. This is good information regarding the back panel. I can easily modify it to use a dado vs groove. Until I can do some further research to understand the physics behind the Quick Lock system, as Michael's comments suggest, the Quick Connect does provide additional "leverage" over the glued tenon. I would like to know if Festool themselves can answer this question. I'm all about the research. I appreciate Chuck's detail in his response. I don't think the Festool quick lock is the same as, say, IKEA's cam lock because of the way the pin pulls together the material through leverage vs radial screw in a cam. But I may need to be corrected. Because I want to keep moving on the project today, I will elect to use four tenons along the 24" joint plus sand a 15mm strip on the  gable where shelves and panels join and use glue. But we should keep this conversation open because it's important to understand better the benefits and limitations of the flat packing option using a glueless assembly.