Dovetail Layout: What Ratio or Degree?
I’ve looked at, photographed and cut many dovetails throughout my days as a woodworker, book author and magazine editor. I’ve written on this blog at least once in the past that the angle used for dovetail layout is in no way consistent in antique furniture construction – you can find almost any slope or angle if you take the time to examine a handful of pieces. So when I hear someone say that dovetails have to be laid out using a 1:6 ratio or a 1:8 ratio, the hair on the back of my neck stands up. And if that’s not enough, you hear others, myself included, talk about dovetails using the degree angle, such as 12 degrees. (I don’t, however, tell you that you have to use 12 degrees; that’s just what I use.)
From where does all this jibber jabbin’ come? Why do some woodworkers talk ratio while others use degree-speak? Couldn’t we pick one method and use it? Here’s my take on this; no, it’s not fact based or found in a 100-year-old book. The left-hand photo shows the “ratio” method to layout the angle of your dovetails. (I used SketchUp to draw and show the angles.)
A 1:6 ratio – that’s one unit horizontal with six matching units drawn vertical – lays out as a 9.5 degree angle. A 1:8 ratio – one unit horizontal with eight matching units drawn vertical – is an angle of 7.1 degrees. I doubt woodworkers in the last century had as strong a passion for being precise as woodworkers today. In fact, my guess is that most 18th- and 19th-century woodworkers simply picked up a saw and went at it. Today there are those among us who would spend time to adjust a bevel gauge to get exactly the 9.5 or 7.1 degree setting.
Here’s the question: Before you read the degree angle of slope created with a 1:6 or 1:8 layout, did you know the exact angle? I bet not. It’s easier to remember the ratio than it is the degrees, so that’s what we do.
In my DVD “Building a Carolina Cellarette” I use a 12-degree angle (and I show you a router setup for dead-flat tail sockets on your pin board). Not because I want to buck the system, but because I like the look and I’m confident that my joinery will hold. I guess I could talk about the ratio, but I don’t think even I could remember the number given a long enough time between dovetailing sessions. Would a 1:4 11/16 ratio be easy to remember? How about 1:4.6875? Don’t think so. What if I simply push the unit dimension to 1:5? What happens then? My degree angle slides from 12 degrees to 11.3 degrees. Would the earth fall off its axis? The answer is, of course, no!
What if we turn all the information into degree angles? You’re not going to remember 9.5 as easy as you might the 1:6 ratio, so let’s tweak that to a 9-degree angle. How would that change your layout? As you can see to the left, that moves the vertical leg from 6 to 6 5/16 units. (If we use inches as our measurement, this makes things a bit easier to grasp.)
If we then tweak 7.1 degrees to straight-up 7 degrees, that changes the vertical leg to 8 1/8 units (inches). Does that help? Probably not.
Does it matter? Probably not. What’s important is that you don’t get the slope so steep that your tails break off and your joint caves. Or that you don’t get the slope too straight that your tails slip from the pins, or that your joint has to rely only on glue for its strength. Between those two extremes anything goes. There are, as you may know, woodworkers out there who don’t take the time to do any layout work at all. With saw in hand, they simply cut dovetails.
So which is it. Do you fall into the ratio camp, or are you a woodworker that uses degrees? Or are you brash enough – some might say reckless enough – to pick up your saw and get busy?
Looking for more on dovetails? Chuck Bender DVD “Dovetailing Apprenticeship” is a great first step. And if you’re searching for couple of ways to get the work knocked out quicker, I highly recommend my DVD “Cheating at Hand-cut Dovetails.”