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When is it more appropriate to use dowel and dowel insertion equipment versus other types of fasteners and insertion equipment?
Mel Hatch, president, Accu-Systems Inc.: Dowels work great for joining panels that are a finished product. Some RTA applications use dowels for alignment and also use metal fasteners for assembly. Generally, dowels can be inserted in a production process much quicker than other fasteners. Many pieces of furniture are not suitable for the use of metal fasteners so dowels are used.
Dowels are very common in non-solid work applications. Many other construction methods will break out. In solid wood applications it is common to see a mortise and tenon joint.
Hans J. Meier, executive vice president, Koch Machinery: Dowel insertion equipment is used for a fast and automated joining of furniture and cabinet components. The dowel leads to a precision connection with pre-drilled locations, which allows for fast, easy and accurate assembly of furniture or other components. The dowel also offers a non-visible joint for wooden components.
Insertion of dowels is a fairly standard procedure. There are many standard machines offered for this type of application in a competitive price range. Machines for metal fasteners have the tendency to be more hardware specific and more expensive than standard dowel insertion equipment.
Most metal/plastic hardware is used for RTA furniture, many times together with dowels, for locations and vertical holding strength. Minifix type hardware as well as Confirmat screws are almost always manually applied in the assembly area or will be packaged with the RTA furniture assembly.
Pocket screws have become popular for assembly of cabinet face-frames, as well as furniture. Automatic insertion of screws can be done, but is usually more expensive than dowel insertion machinery.
The screws seem to be used more for complex lay-ups of face-frames as well as smaller production batches. When using screws the accuracy and precision of the assembly is dependent on the labor force in the assembly department rather than dictated by precision drilled parts.
The assembly process using face frame clamps with dowels is much faster with standard sizes and same size batches.
Pocket screws or Confirmat screws provide instant holding strength without clamping time and can be used to tighten joints in the assembly process. However, because pocket screws are more labor intensive to insert, the extra time required for clamping a dowel joint may be negated by the added cost of screw insertion.
Jason Varelli, North America key account project manager and North America COMIL-RBO product area manager, Biesse: Dowel construction has been introduced to increase automation, productivity and consistency of quality.
It's an assembly method that suits both large and small shops. There are several advantages dowel construction brings to the industry; precision, quality finish, and cost effectiveness.
In more traditional construction methods like dado construction or screws, the precision of the cabinet assembly and the "squareness" of the box is totally dependent on the skills of the person assembling the cabinet. In dowel construction the perfect alignment of all components of a cabinet is ensured by the method itself.
Another reason to move to dowel construction is decreased or reduced labor when compared to traditional construction methods. As your production levels grow, so will your assembly team since it takes longer to assemble a traditional dado or screwed box.
Are there cost considerations when deciding whether to use dowels or another type of fastener?
Hatch, Accu-Systems: Dowels are probably the least expensive fastener available. This may or may not mean that dowel construction is the least expensive assembly method. Although other fasteners may be more expensive, there is a lot more to the equation. What equipment is needed? How much labor is required? Do dowels work well with this material? Is it assembled in house or in the field or must the finished goods be shipped assembled? All of this should be given consideration. The complete process should be looked at and not just the cost of the fastener itself.
Meier, Koch Machinery: Metal fasteners are typically more expensive than dowels, however, customers can save (in the case of pocket screws) machining steps for the mating holes. Screw assembly does not require the clamping time that is necessary with dowel construction. In other words, the screw obtains instant holding strength.
Varelli, Biesse: Yes, you have to look at the total cost of using each type of fastener and their impact on your manufacturing process. You need to look at the cost of manufacturing a screwed together box or a box using dado construction vs. a doweled box. To build a doweled box, you will need additional equipment not needed for dado or screwed together boxes. A typical set of machinery for dowel construction includes panel saw, edgebander, CNC machining center, horizontal drill and dowel insertion machine, and case clamp. You can see a horizontal drill and dowel insertion machine and case clamp are needed for doweled construction while not necessary for traditional construction methods. Depending upon the equipment you have, the parts for a screwed together box and doweled box would be made in almost the exact same time, while using dado construction will require more time. Then, look at the speed and accuracy of assembling each type of box to see which is most cost competitive.
From a strength and holding ability standpoint, which is more reliable, dowels or metal fasteners?
Hatch, Accu-Systems: Metal is stronger than wood. Generally in panel construction, the material will fail before the fastener. In solid wood, often the opposite is true. In solid wood often a mortise and tenon joint is stronger than a dowel or a metal fastener. In solid wood applications many metal fasteners have screws to hold them in place. These screws will often fail. A strong fastener will not make up for a poor design. A good rule of thumb is surface area. The more surface area used in any method of construction is generally the best method.
Meier, Koch Machinery: Screws do have an advantage in solid wood or plywood applications from the standpoint of vertical holding strength. However, lateral pressure applied to a component joined with screws can weaken this joint much more than the same parts joined with dowels. Particleboard and MDF are a particular challenge for screws, since over tightening as well as side shift can cause weakening of the joint with gaps or complete failure of the joint.
Wooden dowels will provide a larger load capacity than metal fasteners, as the vertical shear strength due to the larger diameter of the dowel is much greater. Also, a dowel joint with appropriate glue will offer greater withdrawal strength in wood composites such as MDF, particleboard and plywood.
Varelli, Biesse: I'm not aware of any test on fasteners strength, but it's a mute point since the strength of dowels is more than adequate for typical casework applications. We may debate if metal fasteners are stronger on paper, but due to the fact the fastener is always stronger than the material it's fastening, dowels vs. metal fasteners becomes irrelevant.