Woodworking: A Better DIY Joinery — The Sliding Dovetail

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DIY is all the rage these days. The internet is overflowing with DIY websites, “how to” tutorials, downloadable plans. The popularity of this “genre” is that you can do amazing things with little or no previous knowledge or skill.

When it comes to woodworking, there is a lot to be said for that. There is certainly a broad field of woodworking that requires immense skill (and is often made easier by very expensive tools). Turning wood on a lathe, for example, requires not only a lathe, but a good bit of practice and training to master the technique.

That said, building a picnic table or a bookshelf is something that anyone with very limited tools and woodworking skills can do reasonably well. However, it’s often not that difficult to do things well. Why use a crude and inferior joint technique, if a far superior one can be made just as easily? And that brings me to the subject of this post.

Most of the DIY sites (the ones making money) are being sponsored by a tool company such as Kreg or Ryobi, so they are constantly telling you to join everything with pocket screws using your Kreg jig and your Ryobi drill. I get that they have to make money, but there is a place for pocket screws — I use them often — but why advocate that type of joint when another is called for?

captureWorse, you often see “woodworkers” demonstrating “glue and screw” joints such as the one pictured here. Yeah, I get that he/she is making this with plywood and will putty in the screw holes and paint the entire thing, and in the end the screws won’t show. But it’s an inferior joint for a shelf. The shelf should at least be set in a dado joint which can be cut in less time than it will take you to fiddle around with puttying and sanding at the end of the project — and the joint will be 100 times stronger. And a glue and dado joint for a shelf won’t require any screws — no screws on the outside to putty, no ugly pocket holes on the bottom side of the shelf that you hope no one stoops down to see.

What if you want to build a bookshelf out of cherry or oak? I hope you aren’t planning on painting five dollar a board foot hardwood. I’m here to tell you that you don’t have to settle for painted projects to cover shoddy workmanship. You can build a high-end looking project with the same tools and experience you are putting into the DIY plans you are downloading from the internet.

A dado can be cut with a table saw, radial arm saw, a router, or with a handsaw and a chisel. There is no reason to not at least be using dado joints when they are called for. Sure the dado joint will show at the front of the bookcase, but if you will be using a face frame, the face frame will hide that.

What if you aren’t using a face frame. Let me introduce you to another extremely strong and invisible joint — even stronger than the dado joint — that you can cut in minutes. This will require a router and a router table.  If you are doing ANY woodworking, a router, a table saw, and a miter saw are absolute musts anyway.

The sliding dovetail joint is a locking joint. A shelf could theoretically pull out of a dado joint.  Not so with a dovetail joint. This is a common joint in cabinetry, particularly with drawers. It looks intimidating, but let me assure you a 7th grader can make this joint.

IMG_20160517_183013If I’m using 3/4″ stock, I generally use a 1/2 inch dovetail bit. I set my bit depth to approximately half the thickness of the stock. It doesn’t have to be exact, because we will custom fit the tails to the slot.

The jig is simple. Make a square box with 3/4″ stock laid flat, exactly the width of your router base, so it can’t move left or right. Set the end of the box so when your router hits it (stops), the bit will stop about 1/4″ from the far edge of the board. Clamp your piece to the table and clamp your jig to your piece, and rout your slot. Make a couple slow passes so the slot is cleaned up nicely. Make all your dovetail slot cuts for your entire project without changing your router setup.

Once all the slots are cut, now it’s time to cut the tails. Always do your initial tail set up on a scrap piece of wood. Mount your router in your router table. Take one of your pieces with a slot and turn it slot down so you can see the slot. Raise your router bit until it just touches the bottom of the slot, then lower the bit back down about 1/16 of an inch. You can always tweak later. If your tail is too short, raise the bit. If the tail is too long, lower the bit. I usually don’t need to. You want the tail just slightly shorter than the slot so there will be about a 1/32″ to 1/64″ gap between the tail and the channel for glue surface. If it’s too snug it will starve the glue joint and may also leave gaps in the corner mating surfaces.

Once the bit height is set, move the fence so the bit is barely outside the fence and make a pass on each side of your scrap piece. See if it will fit in your slot. Hopefully it’s way too big. That’s what we want. Now you can move your fence back about 1/16″ of an inch and make another pass on each side. Make very small fence adjustments. Keep in mind because we are making a pass on each side of the board, a 1/16″ fence move results in a 1/8″ change to the tail-piece. Check fit again. Once it gets close, make smaller adjustments to the fence. Once the piece will start to go in, but is still too tight, you can often just make another pass or two without any fence adjustment to clean up a bit of stray material and get a fit. We want a good snug fit. If you need to tap it with your hand to get it to go in, that’s good. We don’t want to have to pound it in with a hammer though.

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It shouldn’t take more than a couple of minutes for this whole process to get the perfect tail set up, then you can cut all your tail pieces with confidence.

IMG_20160517_183346Now that we have a perfectly fitting tail, because we are making a hidden joint, the tail-piece won’t slide all the way in.

Slide it in until it hits. Use a chisel or small saw (coping saw works well) to cut out the dovetail notch extending. I like to saw horizontally across the grain, the take a chisel and tap the piece out vertically with the grain.

Then because the end of our channel is rounded from the router bit, take a utility knife and shave the corners where we just notched out to round it off a bit and you’re done.

IMG_20160517_195926Tap the board back out of the groove, flip it around and slide it back in and — Presto — you have a completely invisible joint that will still be holding strong 100 years from now. A little glue in the bottom of the channel and on the end of the tail is all it takes. Of course, clamp your glue ups until they dry. Usually 30 minutes clamp time is sufficient, but don’t stress the joint for 24 hours.

So just because you are a DIY’er, don’t be intimidated by proper joinery techniques. Most of them can be done well with basic tools and just a little practice. The first time you attempt this, it may take you a half hour or longer, and several pieces of scrap wood to get the setup right. Once you’ve figured it out, the next time and the time after that, you will be knocking these out it minutes.

If you’ve never made a sliding dovetail joint, go to your garage or shop, grab a couple of pieces of scrap wood and give it a shot, then let me know how it went for you. You’ll be making stronger and better looking projects in no time.