Fastening dado joints

      Fast techniques for assembling dadoed cabinet boxes. June 24, 2002

I dado my cabinet box tops and bottoms into the sides, then pre-drill and screw to fasten them. Can I get away with a faster type of fastening system, keeping the dado? Anyone using staples or nails?

Forum Responses
From contributor T:
We dado and staple using 1-1/4" long 1/4" crown staples and yellow glue. It makes a very sturdy box. Put the back on and square it before the glue sets.

From contributor R:
I make my cabinet boxes the same as you. There are two things that always bothered me about this system and I'm anxious to hear what others think.

1) How much is the glue actually doing in these dados? I cut my dados on a table saw (CMT blades) and it just doesn't seem like a dado is a clean enough surface to glue properly.

2) Screws being visible on cabinets sides (even though no one sees them once installed) seem inappropriate in high-end work.

I think a doweling system is probably the cleanest/strongest way to go, although I don't know about the fastest. The problem with doweling is that to do it quickly, you need machinery costing tens of thousands of dollars. You need the volume to justify this cost.
I am soon going to start experimenting with PUR hot melts for attaching face frames. I wonder if these would work with a dado/PUR hot melt/couple of staples system for box construction. I'm not so keen on the previous suggestion of just glue and staples (given my concerns about dado glue surfaces). It just doesn't seem like sturdy construction.

I have been using the Hipur hot glue for eight months. I love it and I've not used dado saws since I got the router attachment plate for my panel saw. Routers make clean dados quickly and you can get any size cutters to fit any type of plywood for an inexpensive price. I also use a staple or two just to hold the boxes until the glue sets up. Now I don't need to clamp them that often.

From contributor T:
One more time - dado and staple. I have been doing this for 25 years and never had a problem. I have a couple of times dropped cabinets while loading them in the truck and they held fine. We edgeband before dadoing, and get a nice tight joint that looks good.

We have done jobs with other cabinet shops. One of the shops just butts the joints with screws, and the other uses pocket screws and butt joints. My opinion is that glued and stapled is stronger than both of these methods. One other shop that I'm familiar with uses a stopped dado, done with a router setup. The only thing I don't like about that is that it looks like a butt joint when assembled and installed, and why go to the trouble to dado if you're going to hide it from the customer? I think casework that is CNCed often uses the stopped dado or dowels. Dowels are probably pretty strong, but very time consuming without some CNC or expensive boring equipment.

As far as strength once the cabinets are installed, any of the methods above is okay. It takes me longer to put a cabinet together with butt joints because I have more trouble lining everything up.

We have a saw dedicated to cutting dados, which is an attempt to have the best of both worlds. Since we don't have to set up the dado blades for each job, we can cut the dados with little time lost, and that time is regained with faster assembly.

I have heard arguments that dadoing particleboard actually gets you down into the middle of the board, which is weaker than the board near the surface, because of the way that particleboard is manufactured. But even if the middle of the board is weaker than the surface, it is still strong enough.

Contributor R, we use stack dado cutters and get a good glue joint. If you're not getting a good glue joint with your cutters, something is wrong. That's what dados are for. If the kind of cutter you are talking about is one of the wobble cutters, you might not get a good glue joint with that, but if you're not getting a good glue joint with a stack set, they need to be sharpened so they are all the same height.

Perhaps one of the larger shops that is familiar with AWI standards could fill us all in on what the joint standards are in Premium grade cabinets, if any.

Contributor R, I have been using dados, glue and nails to assemble cabinets for several years now and I can't imagine a stronger joint - the nails are used only to speed assembly and prevent having to use so many clamps. You certainly need clean, flat dados for strong glue joints.

It takes a little practice to be able to quickly lay down the right size glue bead - I try and put as much in the grooves as I can and still not have any squeeze out. All my dados/grooves are 1/4" deep and therefore require the same amount of glue. I prefer Titebond II for all of my general-purpose wood glue joints.

I use an 8" stack dado set from Systematic. It cuts extremely clean and flat bottom dados/grooves and produces no chipout at the edges of the joint, provided the teeth are sharp and clean.

The 2" finish nails I use are shot from a Porter Cable finish nailer. The nail holes are easily filled with filler and sanded for an almost invisible fill on veneers or puttied with colored putty after finishing. I used to fill all these holes when I first started using nails, but rarely fill them any longer on unfinished ends. Have had no complaints or comments by any customers or contractors. On finished ends, I usually only shoot nails into the top stretchers of base cabs and tops of wall cabs - the holes get hidden by the counter overhang and/or the moldings at top of the wall cabs. I still use clamps for the bottoms/decks of cabinets so there are no nail holes to fill or see.

I'm in the process of moving to frameless so I am currently searching for a suitable fastening method for my shop - I think dados are no longer the answer.

Contributor T, I'm curious how you keep from chipping out your banding on the panels that feed through your saw with the banded edge trailing. Since your dado joints are visible, I assume you are building frameless cabinets. Are you working with 32mm "system" hardware? If so, do you find that dados complicate the "system"?

From contributor T:
Yes, we do mostly frameless. Dados do complicate the system. It is one extra process. That's why we have a saw dedicated to that. Then the small amount of time lost cutting the dado is regained in faster assembly, which is faster because less time is spent lining up the pieces. We run a backup board through the saw with the side when dadoing when the edgebanding is trailing.

I don't know if dados would work in a normal 32mm system. I think the 32mm system that we use is not the "book" system. We use the 32mm system holes for mounting the hinge plates, shelf clips, and fronts of the drawer runners, but I have not yet determined how to use it to mount the backs of the drawer runners in American sized cabinets.

We use a Delta line borer to drill the holes, and because of small inaccuracies that we can't seem to dial out of the machine, instead of indexing off the bottom of the cabinet to start the holes, we index from the middle of each panel.

My understanding of the 32mm system is that this is not the way it is usually done, but it does have some advantages with our limited tools. The first advantage is that it doesn't matter which side is up when you assemble the cabinet, and the second is that the doors are usually interchangeable from right to left on a two door cabinet. That way, as I see it, it is harder to make a mistake when assembling the cabinet or drilling the doors.

The biggest disadvantage to doing it that way is that there is a way to size drawers using the "normal" 32mm system that we are not able to take advantage of. This is not too bad because we use side mount full extension drawer runners almost exclusively, and can adjust the placement of the drawer member of the slides. When we use the hidden undermount slides, we end up drilling the cases for them by hand. Because of the advantage of drawer runner placement, I recommend doing the 32mm system by the book. I would if I could figure it out.

Whatever fastener you use to assemble the cases doesn't matter, since with frameless cabinets, the end of a run is either a finished end panel or a filler. We use staples because they are strong and fast. They also have less of a tendency to cause ripples in the surface of finished veneered panels (an open bookcase cabinet, for instance). Screws will, if not piloted, and sometimes even when piloted.

Good luck with frameless construction. I think you will kick yourself for waiting this long to start using it. The only advice I can think of right now is make sure everything is square. If it is, the process is a breeze. If it's not, the process is a nightmare.

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