Blind Dado Versus Confirmat Construction with a Nested-Base CNC Setup

Cabinetmakers describe their experiences with different assembly methods in CNC cabinet production. December 10, 2007

I have purchased a nested CNC and Cabnetware and am wondering what the pros and cons are of blind dados and dowel and confirmat systems? We are a smaller (5 employee) shop that builds mostly custom frameless kitchen cabinets.

Forum Responses
(CNC Forum)
From contributor J:
Blind dado is the best system for a smaller shop, in my opinion. The difficulty you will have is in the consistency of the material you use for your boxes. Artificial materials work very well with most software, as they base all settings off a pre-programmed thickness. If you use ply and have lots that vary from bunk to bunk, you will struggle depending on your software's capacity to deal with that. I only know Ecab well in the 3D design arena and it deals with this well by allowing this change to be made just before automating a post and adjust all joinery to suit "actual" size. If your software does this you will be okay; without it, more than 15 thou variation will cause problems. With dowel method (we use also), you adjust your horizontal height until you are flush with your mating parts, which are machined in the nest the same way all the time.

Dowel is faster to CNC, as the joinery of blind dado makes longer cycles. We have a 9 position spindle on the CNC, which allows even faster times for dowel if set up properly. The down side is setup and production on another machine to get a complete box. If you have man power and space, and the CNC is your bottleneck, then dowel may be better. If you are limited in these areas and have plenty of open machine time and the correct software ability, then do blind dado.

There are many other smaller issues that come to play here.

From contributor L:
I use confirmats and they work great. Even though my router doesn't cut square and has other issues, the confirmats still work. I use Cabinetpro software, and it has a compensation feature for the variation in thickness, but I've only used it once. I find that if I reference the holes correctly (I use 9.5mm center from the top and bottom edges, for example, and my construction boring machine is set at 9.5mm from the table top), I don't have any trouble that a little adjustment with a deadblow can't handle. If your machine is accurate (which I can only dream of), you should have no px with confirmats, or any other system. I use confirmats because I had a construction boring machine already, and with the correct material and spacing meets AWI premium standards. One advantage to this system when you are first getting your feet wet is that it is very forgiving. You can still use the part most of the time and you can replace any spoiled parts easily with your saw and tack and use conventional screws to build the cabinet without having to backtrack on the CNC right then or wait until the rest of your parts are run to rerun the part.

Average assembly time for wall cab is 5-6 minutes, base cab 8-10, sometimes more because of complexity. Can you configure your cuts and drill patterns yourself, or do you have to have CW do it, or do you need a third party software to operate?

From contributor S:
We also have a CNC and Cabnetware. Here is my advice...

1. Update the Cabnetware to Cabnetworks.
2. Buy an electronic digital caliber.
3. Before you start cutting, check out the thickness of the material, adjust the material thickness in "interior" and "exterior" file, check the box "use the actual material thickness" in preference cutlist.

Use your CNC in the capacity you paid for - blind dado only. Dowels, confirmat screws, case clamps are very old, outdated, yesterday technology.

From contributor A:
Both methods leave a bit to be desired. In blind dado construction, you can't build upper cabinets with edgebanded bottoms flush with the sides unless you flip the bottoms over to have side 6 machining done to mill the tenon for the blind mortise joint. Flipping parts means the potential for human error and the potential for part movement during machining. A horizontal boring machine is essential for confirmat construction, but leaves exposed fasteners that must be hidden in finished ends.

From contributor S:
In your "parameter" file, add the edge banding to the bottom of the cabinet sides. And that's all - simple, no boring, no dowels, no flipping.

From contributor A:
When you build upper cabinets with bottoms flush to the side and you want to edgeband the bottoms of your sides, then the construction method is called a lock dado joint, so you need to mill a dado that is smaller in width than the thickness of the side and then the side is milled down on side 6 so when the cabinet is assembled and you look at the bottom, the joint is totally concealed.

There are two issues with this method:
1. The bottom must be flipped after face 1 machining is completed to mill the tenon.
2. The bottom of the side is compromised so when you run it through the egdebander there is a potential to collapse the thin wall of the motrise.

You will also have the same two issues with drawer boxes unless you want to see a joint in the fronts and backs of your drawer boxes.

From contributor I:
Contributor A, you're wrong about the stop dado construction. Upper tops and bottoms with tendons are a one sided operation.

From contributor A:
With a groove for the back on side 1?

From contributor I:
1/2" or 5/8" back planted on. Why would you groove for the back in frameless construction?

From contributor Z:
What would you do with the bottom edge of the back, band it? We do blind dado our cabs together and the upper bottoms have to be put back in the machine for a secondary operation, either the tenon or the groove for the back. We choose to have our secondary be the groove for the back.

From contributor A:
That is my point. You either flip or you plant on backs. The same goes for drawer boxes but you can't have a totally concealed joint with no mechanical fasteners. That does not work for us for a variety of reasons. It works for others and that is fine.

From contributor I:
Band the bottom edge of the back, the same as the bottom edges of the gables.