Dowel and Confirmat Combination for Cabinet Assembly?

Another discussion of using dowels for precise alignment, plus Confirmat screws for quick, no-clamp assembly. April 18, 2011

I am currently using blind dado on a nested router but would like to switch to confirmats. My reasons are as follows.

1) Ultimately I would like to employ a full dowel system, but as I have neither the money nor space for a CNC bore/glue/insert machine and case clamp, the confirmats would allow me to work in a dowel system (so that I can develop software libraries, SOPs, etc.) without the case clamp and dowel inserter.

2) I use pre-finished plywood which, in my experience, makes for an unhappy marriage with blind dado construction.

3) Save machining time.

4) In theory, assembly could be performed by less skilled labor and likely faster.

My primary question is one of accuracy. If you read through the Knowledge Base it seems that some people are getting dead nuts accuracy regarding their alignment using confirmats, whereas others have to make final adjustments prior to fully tightening the confirmats. One solution that several shops were using to combat this was combining dowels with confirmats, the logic being that the dowels offered perfect alignment with the confirmats then taking the place of the case clamp. For those using this method, how are you inserting your dowels?

Also, why, assuming that I am using construction boring for horizontal drilling and vertical drilling on the CNC, would I have alignment issues with the confirmats alone?

Forum Responses
(Cabinetmaking Forum)
From the original questioner:
Oops, forgot one thing... Does anyone have a suggestion regarding a boring machine? I don't want to over-spend on a unit capable of vertical boring given that the CNC will handle the vertical boring.

This is probably a dumb question, but are the machines available in 8' length, and if not, how do you accurately bore 8' cabinets?

From contributor M:
We are an all dowel/confirmat/MiniFix shop. So I can give you a few pointers and help alleviate some of your confusion... and add more!

When used properly, confirmats do not have any play or ability to adjust. The face bore is the same diameter as the screw shank and the threaded parts body is sized to the end hole. This creates a perfectly tight fit. Confirmats are literally a steel dowel with threads on one end. If you oversize the face bore, the head will tend to over counter sink.

MiniFix is a bigger pain to drill (but if you use the CNC for the 15mm hole, it is easier) but gives some play for alignment. In most cases dowels will still be necessary and eliminate the ability to adjust.

Dowel boring on the CNC can be an issue, but in most cases if the programming is correct it will turn out perfect cases. Ultimately a construction boring machine is the most accurate way, assuming parts are square.

I doubt you will need a case clamp straight away. It takes 3 to 5 assemblers to keep a case clamp busy. It doesn't really save that much time over mallets and clamps. The clamps only need to be on the case for a few minutes, or until the back is glued in. Usually the case is clamped with bar clamps, the back is hot-glued, then it is left there until the next case needs the clamps. The clamps are then removed from the first case and put on the next case. In most situations the worker will have to wrap and prep the first case for delivery. By the time this is done, the second case is ready to pull the clamps off.

I hope you can see the flow of work I am explaining. What ends up happening is the clamping time becomes a non issue. In fact there is an argument that picking up the cabinet and loading it into the case clamp wastes more time. As for squareness, we use triangles cut on the slider from plastic cutting boards. They are super square (our saw is good) and indestructible. And cheap. Glue will not stick to them either. I trim off the corners to make sure the long edges are making contact. We square the case from the back by forcing the square into a corner (the backs are 10 to 15mm inset) and hot-gluing the opposite sides, then pull the square and glue the other two. The hot glue dries in seconds.

If you only get a dowel bore and inset machine (not CNC - they are slower and expensive and more complicated) and do the face drilling on the CNC you will be good. The dowel bore and insert machine only needs 4 heads in most cases. You can stagger the patterns by 32 mm to achieve a 6 or 8 dowel pattern. This type of machine has separate drill/insert heads that slide back and forth by hand easily, then lock on 32mm centers using a pin/hole locator. They can also be locked at any non-32mm point. They are very simple and cost a lot less. CNC drill/insert machines are a lot slower because the machine drills one hole at a time, then traverses to the next point. There is also all the complexity that comes with a CNC machine.

From contributor M:
In response to your 8' boring machine, I don't think there is an 8' boring machine for doweling. You should never need to dowel 8'. Unless you make 8 foot deep cabinets? But for argument's sake, a boring machine can bore an infinitely long panel one cycle at a time.

Sounds like you need to talk to a machine rep or spend some time in a shop that uses these machines so you can get the basics. Try watching videos on Youtube showing the use of these machines.

From contributor B:
I do all of my drilling, both confirmat and dowels on the CNC, face drill and edge drill. Works very well. I do believe my Ayen is more accurate because it indexes from the outside edge of the parts where the CNC indexes from one end and edge. I have learned how to make that limitation work. I only use dowels when needed, as I prefer the confirmats even though I have a case clamp. It sits in the corner.

From contributor L:
We use both dowel and confirmat for store fixtures and commercial case work. There is a much wider variety of shapes in this work than typical kitchens, so our approach may be different. 5x10 nested router does all face drilling. Rectangles that require no face machining may be cut on a CNC beam saw. Parts are banded, then go to CNC 8' bore and insert machine equipped with 3 drilling units (one vertical). There are 4 reference locations on the machine, so 4 different patterns can be run without any changes. Parts have bar code tags for machine setup. As for being slow, it takes the machine about 1.2 seconds to drill 8mm, blow the dust out, inject glue, drive the dowel and move to the next location. Dowels and confirmats can be mixed in any order at any spacing. KD fittings use the top drilling unit. The machine completes the typical base side panel in about the time it takes the operator to unload and reload the opposite end. If all 4 reference stations are in use, the operator can't keep up with the machine. Dowels are totally nonadjustable and some very minor variations creep in to the system. We set our case clamp at the same level as the assembly bench and have a ball top roller, so the assembler doesn't have to lift the case in or out of the clamp. All hardware is put in while the sides are flat on the bench. A one shot glue injector is used for the dowel holes, the case is loosely knocked together and slid into the clamp, back is fixed with hot melt. In the time it takes to get the next case ready, the last one is ready to come out of the clamp. When running at full tilt this cell has 3 people: bore and insert, case clamp, door and drawer installation. Parts are sorted as they come off the bander, moved via roller conveyors and transfer car. Tools, machines, etc. are located to minimize operator movement and effort.

Odd shaped cases and display units are assembled with confirmats or KDs. Confirmats do have a small amount of adjustability - 1/2mm? It's not the slop in holes but in the compressibility of the particleboard core. There are two ways of dealing with the variations: design for them or fight them. Where deemed critical, we use old Phillips screwdrivers sharpened to align the holes for both initial alignment and to tweak the position just before the confirmat is final tightened.

There's always a better way - work for constant improvement. You have to work within your budget - don't get in over your head. Without the sales to support the nifty toys, the fun is lost.

From contributor C:
We run the confirmat and dowel combo too. I run on a ptp and all was done on it for years. We just added a Maggi 21 spindle to the mix to save on the horizontal boring time on the ptp. Dead nuts on? Yeah, but 9.5mm off top or bottom and then center the horizontal boring off that. We know what is up from the dado for the back.

From contributor Y:
The issue is that dowels are a one shot deal. The confirmats can allow slight adjustment with the assembly mallet. Most of the problems will be the front edge flushing. I like the one about a setback of the horizontal shelf to allow for a door bumper.

Drill machines have a series of adjustable stops where you can drill any length up to using the last stop. Find one with a long fence. The Globo was a big seller.

From contributor L:
We've still got an old Globo T machine. It was sold under the Morbidelli name by Stiles, actually made by BZ. Solid machine but like a lot of Italian machines of its day, the scales weren't the best. Gannomat makes a well thought out construction bore.