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Use the right tools to machine dovetail joints

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Tools for Success by Scott Burton
Scott Burton is the sales and marketing manager for Royce//Ayr Cutting Tools. For more info email: sburton@royceayr.com

For centuries, dovetail joinery has remained relatively consistent in design and provided the best possible structural integrity for wooden drawers and boxes.
However, cutting tools used to machine dovetail joints have changed dramatically due to tooling innovations. Much of the R&D has been targeted toward the same goal of providing premium cut quality while cross grain machining many different wood species on many machine variations.

Material:
More recently, birch plywood and other wood composites have gained popularity in fine cabinetry and wooden box markets. Due to the composition of wood fibre and glue layers in plywood products, they can be very difficult to machine. Softer wood fibres and abrasive resins in adhesives have proven to be a difficult combination to cut. Shearing wood fibres effectively, requires an extremely 
sharp cutting edge that quickly deteriorates against glue resins that generate excessive heat.   

Machine:
Machinery innovations have played an important role in finding better ways to produce dovetail joints more efficiently and effectively. A wide range of machines is available in single tool and multi-tool formats. Flat table nested systems have their own programs for machining dovetail joinery from plywood sheet stock. 5 axis CNC machines also make it possible to manufacture dovetails in a traditional format, depending on the volume required.  

Tool:
Regardless of the machine or material, the basic challenge of producing joinery with minimal tear-out remains the same. A variety of tool designs have evolved over the years to meet the challenge of providing premium cut quality during cross-grain machining.
A traditional carbide tipped dovetail router, which has served as the standard for many years, has limitations. Although this type of tooling is manufactured in mass quantities at a relatively inexpensive price point, the tool geometry and soft carbide cutting edge creates some serious limitations on modern machine and materials. Brazed carbide cutting edges are always softer, due to the grade of carbide that must be used during the brazing process, which results in dramatic tool life limitations. The straight flute geometry of this type of tooling is not particularly effective at machining loose-grain material and plywood composite products.
A replacement solid carbide insert system can be used in specific situations. Although replacement insert designs are convenient and relatively cost effective, they are not the best option, as they have many of the limitations listed above for brazed carbide router bits and some additional challenges. Although the premium grade of carbide will allow for longer production runs and convenient knife changes, cut quality will not be any better than a brazed tools and can be worse in some cases depending on knife set-up. The greatest limitation of this system is the durability challenges resulting from tiny screws and threads that are necessary to meet small diameter constraints.
A solid carbide helical dovetail tool is commonly considered to be the best option for effective dovetail machining. Helical solid carbide routers are extremely effective for most applications that require minimal grain tearing. Spiral cutting edges produce the absolute best results possible in cross grain machining of solid wood and plywood composite panel products. Premium grade carbide raw material and optimal cutting-edge geometry always produce the best possible result. This style of tool is also available in upshear and downshear options based on machine and material. The only limitation exists on machines that require ‘threaded shanks’ for mounting interface. Due to the difficulty of grinding threads into carbide rod, it is prohibitive to manufacture solid carbide tooling for those machines.
A diamond cutting edge concept provides tool life benefits that cannot be achieved with any other dovetail tool design. Obviously tool longevity has been dramatically improved by using PCD cutting edges, but the challenge of grain tearing has also been addressed with this design. PCD dovetail routers are designed primarily for machining high volume Baltic birch dovetail products that cannot be machined effectively with carbide. A design with ‘chipbreaker’ cutting edge geometry helps the tool shear off wood fibers of plywood, while maintaining a sharp edge on the abrasive glue lines. PCD tools may not provide equivalent cut quality as solid carbide; however, PCD will hold an edge much longer on abrasive materials resulting is a much more consistent quality result. The extended tool life will also produce dramatic labor savings on multi-spindle machines 
that are notorious for tedious tool set up. 

Recommendations
Depending on application and material, there are generally several cutting tool options that can be considered. In dovetail joinery production there are really only two that can be considered good options. Solid carbide spiral and diamond are the only options that will provide value and performance on a variety of materials and machines.
Solid carbide spirals will perform on virtually all materials and provide the absolute best-cut quality achievable in dovetail operations. If the machine 
being used does not require ‘threaded shanks,’ then solid carbide should be used as the preferred choice.
PCD routers are a good option for ‘threaded shank’ machines, particularly if plywood materials are being used in high volume. Multi-spindle machines often require diameter consistency, which can be provided more accurately with a PCD tooling.
Dovetail tools are relatively simple in design, however, depending on machine model they may vary in thread type, tool rotation, shank style and shear angle, so don’t hesitate to contact your tooling supplier for product and application support. 

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