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Dovetail Design

1984 by Mark Dugenske, originally published in Wood News Issue 14, Summer 1984.

The exposed dovetail is both a structural and a design element in modern furniture. The idea is to expose the construction detail and to incorporate it as part of the design. This is in direct contrast with the goals of the past when structural elements were hidden. Moldings were used to cover the crude structural dovetail, ornamentation was then added in the form of carving. This change is perhaps reflective of the openness of our modern society. 

Our "openness" isn't without problems. A joint which is meant to be seen is different than a covered joint where the only goal is strength. An exposed dovetail requires more technical expertise. Exposure of a joint also demands aesthetic judgment. The relationship between design and technique is complex. Good work requires a compatible blending of the two. Design without technical skill or consideration is superficial - it places the cart in front of the horse. When we begin to design things, we usually avoid creating pieces beyond our technical ability. This is how it should be. As we gain skill and confidence we can expand our repertoire. As our understanding increases, we develop a better grasp of design considerations. Part of the design process is the visualizations of the options available. Good design involves making the best choice of options. Design is not a black-and-white situation; in fact, the resulting product is often a shade of gray. 

The following is an attempt to explore visually the various factors that affect dovetail design. It is a collection of alternatives, each slightly different from one other. These drawings should help you visualize the options available when designing a dovetail joint. The quality of one's work is the result of the many individual decisions along the way. 

Dovetail Tail and Pin
Figure I. Dovetail Tail and Pin

We will start with the review of dovetail anatomy. They dovetail is a locking joint consisting of two elements: the pin and the tail, for which the joint is named. The pins and tails only fit together from one direction. The single dovetail joint can either be a complete pin or a complete tale (Figure I). The multiple dovetail usually ends with a half pin on the corner; the half tail is usually avoided (Figure II). The tail board is a mirror of itself. Each side is identical and each side can function as either of the inside or the outside of a box. The pinboard sides are not identical and thus not reversible. The outside of the pinboard is the side towards which the pins are tapered (Figure III). 

Dovetail Angle

 

Figure II. Dovetail Half TailFigure II. Dovetail Half Tail

Figure III. Dovetail Pinboard And TailboardFigure III. Dovetail Pinboard And Tailboard

The dovetail angle provides the mechanical lock. The angle of the pin (pictured in black) mates with the angle of the tail and that contact point is the workhorse of the mechanism. If the angle is too slight, the pin can slide between the tails and the locking mechanism is insufficient (Figure IV). If the angle is too great, the wood at the corner becomes too fragile and will easily break under stress (Figure V).

Cinderella Dovetails 80 Degrees The gray area between the two extremes is an angle of roughly 80゚ (Figure VI and VII,c). A couple degrees either side of 80゚ does not make a great deal of difference. What is important is that the pin and the tail have the same angle and fit closely without gaps. On some of the softer woods such as pine, an angle of 82 to 83゚ is suggested (Figure VII, b). The dovetail router bit is an angle of 14゚ (Figure VIII,e). This angle is not the strongest nor most desirable, but the large surface area of the many pins and tails creates a strong joint. Care must be used, particularly on hardwood, when using the 14゚ router bit so that the corners are not broken off (Figure V). The tendency for the corners to chip is particularly disturbing when the tails will show, as with through dovetail's.


Dovetail Pin Spacing 

Dovetail Pin SpacingFigure VIII. Dovetail Pinboard Spacing

Dovetail Pin RatiosFigure IX. Dovetail Pin Ratios

The spacing of the dovetail pins in relationship to each other is an important design consideration. The spacing is best measured from the center of the pin (Figure VIII a). If the measuring is done from the outside corner of the pinboard, the pins will be bigger than the tails (Figure VIII, b). If the measurement is taken from the inside corner of the pinboard, where the pin is the widest, the tail will be bigger than the pin (Figure VIII,c). 

Figure IX is an illustration of various pin spacing ratios. The 1 to 1 ratio of the pins and the tails is very mechanical looking. This is the type of joint created by a router jig or an industrial dovetail machine. This mass produced look is not consistent with high quality work. It is often used and is acceptable for kitchen cabinets. The other ratios are much more attractive looking. A ratio of more than 3 to 1 should be avoided as it strength of the joint becomes questionable as the pin size decreases in relationship to the tail size. 

Three factors have an effect on the spacing of one pin to another. The examples in Figure X, XI, and XII are one to one ratios. 

Dovetail Pin SizeFigure X. Dovetail Pin Size

Dovetail Stock ThicknessFigure XI. Dovetail Stock Thickness

Dovetail AngleFigure XII. Dovetail Angle

Pin To Tail Ratios 

Figure XIII. is an example of various spacing ratios of the pins (black)and the tails (white). The strongest joints would be the two middle examples, (d. and e.), because the pins and tails are similar in size and therefore strength. The weakest example would be a. and .h., the two on each end of the spectrum. The small pins of a. and the small tails of h. would both break easily under stress. It is interesting to note that small pins such as the one in example a. were in vogue for a period of time in expensive European pieces. The small pins are considered elegant looking. Examples b. and c. are the combination of strength the of d. and the looks of a. Examples f. and g. wouldn't be used because the tail is extraordinarily larger than the pin. 

Figure XIII. Dovetail Pin to Tail Ratio
Figure XIII. Dovetail Pin to Tail Ratio             XIV. Dovetail Spacing Options

Variable Pin Spacing

  Dovetail Pin And Tail Variation Figure XV Figure XV. Dovetail Pin And Tail Variation

To avoid the mechanical look, the pins may be space so that tails are not equal size. Figure XIV. is an illustration of the various possible arrangements. The design created should be consistent with the need for structural strength. If the pins are not evenly spaced as in d., the pens should be closer to the edge of the piece as in f., g., and h. The close proximity of the pin to the half pin on the corner provide extra strength. A dovetail will usually fail on the corner rather than the middle, so it makes good sense to reinforce the corner. If the pins are too close to the middle of the board as in a., the two pins provide little more strength than a large single pin. Example e. is one that I find most visually appealing.

Figure XV. illustrates some of the myriad possibilities one can achieve by mixing the various combination of pin and tail spacing. All are shown half a tail angle of 80゚.











Learn more about Understanding Dovetails - The Dovetail Story by Bill Stankus originally published in Wood News Issue 21, Summer 1988.

Additional information Dovetail Hints and Tips

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