Blind Dado Joinery Versus Dowels or Confirmats
A cabinetmaker asks whether he should switch to blind dado construction to eliminate a boring and screwing step. April 24, 2014
Question
Does anyone build cabinets with blind dados run on nested base routers? We are a 30 man shop with lots of work, and are always looking for little things that add up with lots of production. We currently run our cabs on a 2 sheet 20' bed nested base router. Our construction is confirmat. The router drills everything but the end boring for the confirmats. We take those to a second machine. I'm considering blind dados to bypass the second machine and labor and cost of confirmats.
Forum Responses
(CNC Forum)
From contributor L:
What holds the cabinet together? Glue and staple?
From the original questioner:
Yup, that's what I was thinking.
From contributor T:
We do it every day with Cabinet Vision and I love it. I held onto my dowel machine after I got the CNC but never touched it again. We glue and screw unfinished ends. Glue only on finished ends. Very fast.
From contributor M:
I see the pull for this type of construction. Although I have used confirmats many years now and am very happy with confirmats in our situation, the concept of switching to blind dado has its appeal.
A couple of things to keep in mind. One is that with all the variation in sheet thicknesses, you may wish to skim your tenons to a consistent thickness.
I prefer drywall screws to staples. Maybe I am just a nut, but I have seen so many cheap cases wiggle around after a few years with the staple only method that it just turns me off. You pop a couple of 5mm through holes in the dado and you are all set. Location of the part by means of mortise and tightness by the screw.
Another is it presents a bit of a challenge with finished ends. Some may address this by toe nailing the ends on, which looks sloppy to my eye, and others by utilizing applied finished ends. I dowel finished ends and confirmat unfinished.
My overall assessment really boils down to this, for a very small shop, one or two guys and little or no time constraints on the router, use dados. For a mid size shop, say 500 K to 3 million or so in straight casework a year, confirmats. They are simple, versatile and quick and you don't clutter up the shop with unneeded machinery.
For a large shop such as yours, my feeling is that investment in a doweling machine and case clamp is worth it. No finished end issues, fast as can be, if the clamp rotation is too slow, use an RF glue setter. For a seriously large operation, with a lot of stack cut sheets and repeated patterns, go old school with a beam saw and point to point.
Now I am just making talking points here, there are a lot of higher volume guys that use dados and smaller guys using point to point. Every shop has a different set of circumstances and many are just stuck with the equipment and company mindset that already exists. Product mix also weighs heavy in this equation. One shop does 30 percent volume in boxes, another does 90 percent.
I just think you may want to at least consider moving a 30 man floor towards dowels rather than dados.
From contributor H:
I am a two man shop. We switched from blind dado/staple to confirmat. We first did all boring on a Maggi 2332 horizontal/vertical and added a Weeke PTP in December and now only bore horizontal on the Maggi. I really like the quality of assembly with the confirmat vs glue and staple construction. Much cleaner, no glue, and sturdier assembly even before the back is hot melted in. Your volume is much greater than mine though, and I would make the move to dowel insertion and case clamp with that volume.
From contributor Y::
2 man shop and we use confirmat. Whilst one sheet is being CNC processed, one man can horizontal bore, edge and bin waste of the previous sheet. And the units go together perfectly.
From contributor E:
Blind dados for us, ever since we started using a nested router. Material thickness becomes a critical factor. We switched to calibrated core materials and we measure each unit's thickness before sending parts to the router. Other than that, it's fast and easy. We glue and tack the joints with staples, then add screws to lock it all down. Just like the Confirmat setup, you can pre-drill the screw holes on the end panels to speed things up a little.
From contributor P:
Some like the Tenoncam system.
From contributor B:
I'm a small shop using dowels primarily because I do a lot of finished ends. I'd like to work confirmats into the mix for unfinished ends but I don't see how this would be faster. You've still got to face bore and end bore, so where do you end up saving time? Is it the clamping step?
From contributor L:
It's the case clamp that reduces clamping time to very little.
From contributor B:
Okay, let me rephrase then. Is there any reason that confirmats would be any faster than doweling? Maybe the posts I'm reading have to do with the initial setup for doweling being more expensive and involved than for confirmats. But assuming you've got the setup for doweling, is there any reason you'd want to also do confirmats?
From contributor L:
Dowels and/or confirmats? If you are just making simple boxes and are set up for doweling (CNC, bore and insert machine, case clamp), I don't see any reason to use confirmats. But If you are manually (bar or strap clamps) clamping, the confirmats are probably faster. That still leaves you needing an alternative finished end solution. The old style case clamps are slow to setup by comparison to the clamps that carry the top clamping on a beam or, better yet, just the multiple vertical and horizontal interlocking beams. Bigger shops will use automatic flow through clamps.
For shops doing commercial work, the usual is to follow AWI box construction specifications. You can use dowel or Confirmat construction.
There are times when doweling doesn't work because of the shapes involved. Confirmats are our choice there. Always try to stay within the system that you are best set up for. 80/20 rule!
