Cabinet Carcase Fastening Method Debate

Here's an enthusiastic slam-and-jam discussion of preferences concerning how to assemble cabinets. April 14, 2010

I'm thinking about going from rabbet and dado plywood casework, to butt joints and Confirmat screws in melamine. But I'm not sure how I'd get and keep the cases square. Right now, I can't afford case clamps, so I use shop made right triangles clamped to opposite corners, while the glue sets. Do most people use Roo Glue on melamine butt joints to keep the cases square? And how should I get the cases square to start with using butt joints and Confirmat screws? Is it difficult?

Forum Responses
(Cabinetmaking Forum)
From contributor S:
I am assuming that you apply your backs to the cabinet carcass; I have my backs inset into the cabinet. When the back is cut square this will keep the cabinet square for you.
Then I staple with good staples, weld-bond glue, and add a few screws where needed - mainly the front butt joints and the corners of the back.

I have used this method for years. Top and bottoms are cut the same time that you cut the back, ensuring that they are exactly the same. Once you have this method down you will find it is much faster for cutting and assembly. Top and bottom onto the back then the side gable onto the center section of the cabinet, lining up the front face. I also leave the back height 1/2 mm less to allow for the slight differences in melamine or ply thickness.

From contributor J:
Contributor S has it right on. No matter how do your backs - groove, rabbet, plant-on, etc., once it's attached with screws or staples, it will hold the case square. On a side note, I staple and screw my cases together. What benefit is there to using a Confirmat over a regular particleboard screw? Seems to me that the Confirmat only adds cost.

The advantage of Confirmats over regular screws is the amount of surface that the screw has. They are about twice the size, which would give them about four times as much surface area to grab the material. I not only use them on melamine, I also use them to assemble plywood boxes. Just some extra piece of mind. If a typical 30K job costs me an extra 20 bucks for Confirmats instead of wood screws, that is not a big expense in the grand scheme of things. And... if you ever have to disassemble a box and put it back together, you can go right back in the same holes.

From contributor J:
I would think the particleboard is the weak link, not the screws. If you are using 19mm material and drive a Confirmat with a diameter of ~8mm into it, assuming you get it perfectly centered, that leaves you with only 5.5mm of particleboard on each side of the screw. That's not a lot of meat to prevent the particleboard from exploding.

I'm not arguing that it isn't strong enough, as I know it is. It's used by lots of people with no issues. I just don't see how it's any stronger than a number 8 particleboard screw, or even a number 6 for that matter. The wood is going to give way before the screw. In fact I would be willing to guess that the #8 or #6 screw can hold more weight before the panel explodes than a Confirmat can, because of the extra material thickness that surrounds the fastener. You can go right back in the same holes using a #8 screw as well.

From contributor R:
Confirmats are not used for their holding strength (which is not much more than assembly screws). They are used because the holes are pre-drilled in the two pieces and it automatically aligns the pieces when being assembled. There is no need for glue or case clamps. The screws are the clamps. The backs hold the cabinet square. Confirmats are faster than the staple screw method, but only when you have the proper equipment like a CNC and a CNC horizontal borer. All this being said, Confirmat construction was intended to be used in a high production environment. If you are not high production (CNC equipped) then the staple screw method is the fastest (and strongest - still no glue needed).

From contributor V:
Confirmats only make sense when used with machine bored pilot holes. I use them wherever I can because they (and the pilot holes) align and square the joints.

From contributor J:
Now that makes more sense. So it is the same principle as using dowels, except you don't need to glue in a dowel. So unless you have the proper boring equipment, you should maybe look into staple and screwing instead of Confirmats.

From contributor B:
Confirmats are vastly superior to assembly screws - this is why they are accepted as AWI premium grade joinery, and assembly screws are not. Confirmats are designed to be used without glue. The larger diameter of a Confirmat screw improves joint strength because it allows the threads to bite into the denser outer edges of particleboard. It is also more rigid than an assembly screw. Confirmats make sense whether you manually bore the pilot holes with a step drill bit, or you pre-bore with an assembly boring machine. Either way works. An assembly boring machine is not a prerequisite for Confirmat assembly.

The back squares the cabinet. All your cuts need to be nearly perfectly square and perpendicular or you'll have problems. Don't use glue with Confirmats - it's not necessary. But use proper spacing; 37mm from the edges and no more than 128mm on center.

From contributor A:
I used Confirmats for 19 years. For 3 years we hand drilled with a Zentrix jig, and for 16 years we used a point to point to drill the holes. When we went to a router about a year ago, we switched to #8 x 1 3/4" wood screws. After assembling and installing thousands of boxes over the last 20 years, I'd say that Confirmats are no better than wood screws.

From contributor I:
I have used Confirmats for years for the very reasons contributor B gives. After a long evolution in cabinetmaking, I've settled on Confirmats as a reflection of the quality work I want to do. There will always be the dowelers, screwers and gluers out there looking for the best way to staple a back on their melamine box. Who cares! I just show my customers how their kitchen will be assembled, along with the other details and hardware and I'm selling jobs.

From the original questioner:
I forgot to say that my melamine has an MDF core. Make any difference?

From contributor U:
We bang a boat load of cases together a week. One thing I would say is, get it done. The Confirmats are great and we use them, but we are set up for them. We are set up to notch 1/4" backs and use 1/4 for our backs.

From contributor N:
The Confirmats are engineered for particleboard. The deep threads give the holding power. I sell this to my customers. The benefit is when the holes are predrilled on a CNC, the parts line up perfectly, there is no need for the nail gun and no guess work. The real benefit is that the CNC also drills drawer glide and hinge mounting plate holes. Cabinet assembly and finish assembly is quick with no guess work and you get dead nuts accuracy. I actually use the Confirmat/dowel system because I don't like applied finished ends, so my finished ends are integral and they are doweled. I use glue and just tack them together with no clamps and it works fine for us.

From contributor L:

I didn't know anyone still used wood screws for anything! Build it strong enough and don't waste time thinking it to death. Particleboard screws and melamine glue are probably fine as long as you have good tight fits. Having used several methods over the years, I've ended up with nested 3/4" mel, dowels on a CNC bore and insert machine, all hardware installed before assembly, glue injector, case clamped, 1/4" back in groove with 3/4" nailer. Back is installed while in case clamp and held square. For odd shapes we still use Confirmats, pilot holes done with the second drilling unit on the bore and insert machine. Process produces square, solid cases in a reasonable time frame. We build to AWI specs because we are an all commercial shop. Once setup for AWI it costs no more than the staple, screw and glue system. Confirmats are stronger than #8 particleboard screws, but if the screws are strong enough for your use, then it doesn't matter.

From contributor A:
If I take my 1/4" cabinet stapler and whack 1 1/2" staples every 3 inches in the edges of a box, I promise you no one on this forum will refute the strength of smaller fasteners.

However, AWI doesn't like staples or screws. They like dado and rabbets (we like them as well), so I throw my staples at my highly indexed precision dados and rabbets with a little glue because I like how it sticks to my fingers.

We don't use melamine for anything besides workbenches. So I have no idea if the Roo Glue is worth it or a waste of time.

From contributor B:
Yes, MDF core makes a difference. It splits easier than particleboard due to its structure, and is heavier and more expensive to boot... Not sure why anyone would use it over particleboard with melamine facing, to be frank. In my experience with MDF you need to hold the Confirmats further back from the edge, closer to 2", to prevent splitting.

From contributor C:
We use Confirmat screws in our shop and pre-drill the edge holes with a boring machine, then shoot the joint with the pinner to hold the joint while drilling the remainder of the pilot hole. My opinion is that screws will never beat nail/stapler with no glue when it comes to assembly speed, but the quality of the Confirmat joint far exceeds the time you save with staples.

From contributor R:
We do not know for sure why the AWI chooses their accepted assembly methods. They do tend to like methods that are automatic (CNC or boring machine).

Confirmats are designed to be used without glue. The size of the Confirmat does not have any significant bearing on the strength of the joint versus an assembly screw of similar length. Confirmats make sense whether you manually bore the pilot holes with a step drill bit or you pre-bore with an assembly boring machine. Either way works, but manually drilling is much slower than the staple/screw method.

Confirmats were invented in Germany in the 1970s. They were originally made to work with the 5mm system holes and evolved into what we use today. The larger shank of the screw was born from the size of the other system holes that were already being used, not for added strength.