Perfect Tapered Sliding Dovetails in Wood…BY HAND.
“Time is the greatest thief in life. — Kazeronnie Mak
Off and on for the past couple of years I have been chasing a way to cut tapered dovetails with our HP6v2 Mini Multi Plane. For the uninitiated, a tapered sliding dovetail just may be one of the most difficult joints in woodworking when attempted by hand.
CAVEAT: I have made thirty or so tapered dovetails in my past furniture making life and none were by hand–all router work. That said, in order for this joint to perform as intended, regardless how it is made, the accuracy required can be daunting.
During the research phase of this project I came across some old “dovetail” planes and none of them work the way we are going to show you. Furthermore, you will find few who claim these planes work well at all. All of the planes mentioned cut a dovetail with the stock horizontal to make the male, and the female dovetail? Well, since I never made one by hand, it appears the shoulders are cut with a saw and then the waste removed with either a router plane or a shoulder plane. I wanted one plane to do both. And in order to accomplish that, we had to invent a new way to make a plane iron.
In addition to the iron, we addressed this project from a series of constraints which include;
1) The male dovetail, regardless of overall width, will always be .300″ tall.
2) The longest female dovetail made with our system is just over 20″
3) We will use either the 3/8″ or 1/2″ wide dado kits for the HP6v2 to remove the bulk of the waste.
4) The included taper will always be 1/2 of a degree
5) Joint layout will always involve the centerlines of the male and the female without fretting about stock thickness.
6) The tapered male dovetail will always be made first.
It is the nature of sliding dovetails that you rarely, if ever, cut with the grain. The male is a cross grain cut, and the female is not only across the grain but is primarily an end grain cut. We needed a new way to make a dovetail iron and the results are illustrated below (without the body or fences for clarity), a circular scoring cutter makes the end grain slice and the iron shear cuts the taper (FYI: the bottom of the iron never cuts);
Sharpening this iron is ridiculously easy–hone the “V” groove on the corner of your sharpening stone. Lateral adjustments are made possible by a tapered wedge (pictured below) that uses the side of the plane body as an anchor–up and down movements will move the iron left or right. In practice, we like the iron set to take a cut in the 0.002-005″ range. Because the cuts are light, multiple passes are easy.
The depth of the male dovetail is fixed at 0.300″. To cut the taper, we are making a “left and right” aluminum guide that has a 1/4 degree taper–the combined cuts make a 1/2 degree tapered dovetail. In the image below you see this guide being set up with a depth gage–this is important to prevent a compound cut. In addition, you will always “flush” the edge of your guide with your stock to keep the dovetail centered on the stock. (You can still make off center dovetails if you choose).
Once the fence of HP6v2 is all set to remove as little as possible material at the widest point of the dovetail (we really like anti-friction tape on the fence face!), it looks like this :
As long as the tapered guide is set flush to the edge of the narrow end of the dovetail for both cuts, your male dovetail will be perfectly centered. You make as many passes until it no longer cuts and repeat on the opposite face–use backing boards to prevent blowout on the exit cuts if important.
The heart of our system to create flawless and perfect sliding tapered dovetails is the dovetail gage. This device literally measures the tapered dovetail width at the narrowest end. The vertical flanges on top of the gage represent the ideal dado width and can be measured with a dial or digital caliper. This will require the bare minimum of wood removal to create the female dovetail. Again, this tool needs to be flush set the the same edge.
As mentioned earlier, you can use either the 3/8″ or 1/2″ dado kits for the HP6v2. We are using the 1/2″ here and the first order of business is to retract the blade and set the tool in the depth gage as pictured below (there is a relief cut in this gage so you don’t have to retract the nicker);
Now we can attach the new depth fences to the HP6v2 so they rest perfectly on the top of the depth gage;
Your next step is to layout centerlines for the female dovetails and then set up shop made guide fences 1″ away and parallel to a centerline. For this illustration, the flanges on the dovetail gage measured exactly .5″ (this will NEVER happen, but bear with me…). Once the dados are cut, flip the dovetail gage upside down and into the dado making sure the narrow end is where you want the narrow end of the female dovetail as indicated by the arrows.
Our project looks like this;
The outside edges of the dovetail gage are each tapered 1/4″ of a degree. We will now use these edges as a guide for out reference edges;
With the dovetail gage removed (lift up or slide backwards) the female dovetail can be cut–up one side and down the other using the EXACT same setting used to cut the male.
The results will be dead on. Now back to the dado width… each and every dado you will need to cut will likely be different because of stock thickness variations. Which is why we will offer the coolest adjustable fence that will allow you to dial in any dado width you need…
The white strip on the outside edge is MDF so you don’t have to bugger up the aluminum clamping to your stock. Once clamped, you can adjust the width in 0.001″ increments using the built in Vernier;
This adjustable fence has lots of uses in the shop other than sliding dovetails–it is darn cool. Let’s say your dovetail gage indicates you need a dado that is .524″ wide. Set the Vernier to zero, lock the fence down 1″ away from the centerline. Now adjust fence 0.012″ and make your first plow cut. When complete, adjust the fence back to zero and then another 0.012″ for the final pass. Viola! …524″ dado.
Remember when we set the dado depth fences with the blade retracted? To make the dado you will need to advance the blade 0.002-0.004″ which will make the female ever so slightly deeper than the male–this is a big deal so those flat surfaces do not interfere with each other–your shoulders will suck in tight. So there you have it…
I am betting very few (or maybe zero) of the Drivel Starved Nation have ever made a perfect tapered sliding dovetail by hand. Now you all can–how cool is that? Let the dialog begin!