Chapter • 5

10 Tips for Tight Joints

BY POPULAR WOODWORKING STAFF

You’ve cut all your pieces and are putting everything together when you first notice it – a gap. A dark void where there should be none.

Don’t panic – it happens to the best of us. For whatever reason, there are instances when your joints just don’t fit perfectly and you have to decide what to do: Do you scrap all the time, energy, money and hard work you’ve put into the project and start over, or do you just let there be a little gap and move on?

Well, we’re giving you a third option. We put our heads together and have come up with a list of the best tricks to help you tighten your joints. These tips should help you eliminate those unsightly, embarrassing gaps and point your joints in the right direction.

Compression Makes Dovetails Tight

Hand-cut dovetails are some of the most challenging joints to fit perfectly. Many woodworkers will spend hundreds of dollars on router jigs or woodworking classes to get an airtight fit.

If you decide to hand-cut your dovetails, there are a few ways to make sure you get it right.

Because wood is – on a cellular level – similar to a bunch of soda straws glued together, you can compress it a little bit. Usually, compression is a bad thing, such as when you drop a hammer on your work and it dents. But a little bit of compression is good when dovetailing.

Here’s how it works: Cut the first half of your joint as you usually would – I usually cut the tails first. Then use that first half to knife in the second half of the joint – in this case, the pins.

Next, when you saw your pin lines, don’t saw right up against the knife line you marked, as most books tell you. Instead, saw slightly wide. How wide? The whisker of a gnat would be a good place to start. Here’s how I do it: After I knife in my joint lines, I run a pencil over each knife line. Then I start my saw cut to leave the entire pencil line.

Like all things pertaining to dovetails, this takes practice. Cut some sample joints to get a feel for it and use a magnifying glass to gauge your progress.

Once you cut your pins, use a knife to ease the inside edges of your tails, which will be inside the joint. When you join your two pieces, the too-tight pins will compress the tails and the joint will be seamless. If you try to compress too much, one of your boards will split as the two boards are knocked together.

This compression works especially well with half-blind drawer joints where you are joining a secondary softwood for the sides (such as poplar) with a hardwood drawer front (such as oak), because the softwood compresses easily. But be careful: This trick doesn’t work when you are trying to join two pieces of dense exotic wood, which doesn’t compress much at all.

— Christopher Schwarz

Fake Half-blinds for Dovetail Joints

Half-blind dovetails are trickier to cut than through-dovetails, but they don’t have to be. I picked up this trick from dovetailing maestro Rob Cosman, who has two excellent videos on dovetails.

Essentially, you first build a drawer with the easier through-dovetails and then glue a ¼”-thick piece of veneer over the drawer front, making them look like half-blind dovetails.

Usually with drawers you have ½”-thick sides and a ¾”-thick front. To do what we’re suggesting, make your drawer front with ½”-thick stock, too. Then join the sides to the front using through-dovetails.

Wood compresses, and you can use that to make your dovetails tighter. Cutting your pins just slightly wide will force them to compress the tails.

Through-dovetails are easier to cut than half-blinds. To make life easier (and to stretch your stock of valuable wood) cut through-dovetails when joining your sides and drawer fronts. Then add ¼"-thick veneer to the drawer front.

Then, using your band saw, resaw a piece of ¼”-thick veneer from a piece of really nice figured wood. Make it a little larger than the finished size of your drawer front. Then glue that veneer to the drawer front, let the glue dry and trim it flush.

This makes excellent half-blind dovetails and allows you to stretch your supply of nicely figured woods for your drawer fronts.

— CS

Deeper Mortises Close Gaps

It’s easy to get gaps when using a traditional mortise-and-tenon joint. Luckily, it’s also straightforward to get rid of them.

If you make your mortises exactly as deep as your tenons are long, you’re asking for trouble. By doing this, you haven’t created a place for any excess glue to go, so it will be forced out of the joint. And if there is even a little bit of gunk at the bottom of your mortise, the joint won’t close tightly no matter what you do.

To fix this, make your mortises ” deeper than your tenons are long. This trick will save you time because you don’t have to clean up the bottoms of your mortises as much, and it will prevent glue from squeezing out if you use too much in the joint.

— CS

Paring Your Shoulders in a Mortise-and-tenon Joint

Before you assemble your joints, you should always clamp them up without glue. That way, you can disassemble everything and fine-tune your joints if you find ugly gaps at this stage. But what if you can’t track down the problem? We’ve found that tuning up the shoulder of the joint will help you fix a variety of problems and make sure you don’t hurt the strength of the joint.

First, clamp the tenon in your bench’s vise with the tenon pointing straight up. With a sharp chisel, pare away the inside of the shoulder without cutting the outside of the shoulder that shows. Pare away about ” all the way around and then test the fit again.

This should help you solve problems where your shoulders are angled a bit because of miscutting. It also helps out when the tenon’s mating surface isn’t perfectly square – it’s quite common to sand or plane that area so it’s bellied a bit.

— CS

Use your workbench as part of your clamping setup when applying the veneer to the drawer. This setup helps spread pressure evenly across this large surface.

Making your mortise a little deeper prevents gaps at the shoulders.

Tighten Mortise-and-tenon Joints with a Shoulder Plane

A common problem with a mortise-and-tenon joint is that it’s easy to make the joint too tight (so it won’t go together) or too loose (where it will fall apart).

Even expertly machined joints have this problem because it’s tough to hold all your parts with exactly the same pressure as you cut them on your table saw or router table. A ¹⁄₁₂₈” difference can make or break this joint.

Your tenons should slide into your mortises with hand pressure only. The fit should be firm but not forced. To get that every single time, I make all my tenons so they are slightly oversized. Usually I shoot for a tenon that fits a bit too tightly but would go together with a mallet.

Then I get ready for a dry assembly and use my shoulder plane to tune up each joint. A good shoulder plane removes just a couple thousandths of an inch in a pass. This allows you to sneak up on a brilliant fit with only five or six swipes of the plane. It takes about 10 seconds per joint.

Be sure to remove the same amount of material from each face cheek of the tenon by taking the same number of passes on each side of the tenon.

Shoulder planes are available new from Lie-Nielsen, Clifton, Stanley and some other custom plane-makers, such as Shepherd Tool. You also can find them at flea markets or on the Internet.

— CS

Add Rabbets to Dado Joints

Dados are deceivingly simple: You just cut a trench in your work that is exactly the same width as the thickness of its mating piece.

The problem is getting the dado sized exactly right so you don’t have an ugly gap at the front of your joint or along the trench where the boards meet. Of course, to precisely size your dados you can use shims in your dado stack, buy undersized router bits or cut your joint in a couple of passes.

Another option is to cut a rabbet on the mating piece. Using a rabbet requires an extra machinery setup, but it is worth the trouble. Cut your dado so its width is ⅛” undersized. For example, if you were planning on a ¾”-wide dado, make a ⁵⁄₈”-wide dado instead.

Pare the shoulder all around the tenon to help eliminate gaps in this joint. Be sure not to cut the edge of the shoulder, or you’ll make your gap worse instead of better.

To get your tenons fitting perfectly, learn to use a shoulder plane. This handy tool will fit your tenons in an extraordinarily controlled manner.

Dados are a pain to get sized just right. So don’t bother sizing the dado to the material. Cut the dado undersized and then cut a matching rabbet on its mate.

A sharp and tuned smoothing plane can reduce your thickness in small increments, allowing you to sneak up on a seamless dado joint.

Then cut an ⅛”-deep rabbet on your mating piece that allows the two pieces to nest together. You can tweak the size of the rabbet to get the joint just right.

— Steve Shanesy

Use a Hand Plane for Dados

Another way to get perfect dados is with the help of a smoothing plane. If you can sharpen and set up a plane, this is for you.

First, cut your dado so it is slightly undersized. I’ve found that the dado made by dado stacks is always a few thousandths of an inch less than the width you require. To cut a slightly undersized ¾”-wide dado, I merely install all the chippers for a ¾” dado. This has always worked, regardless of the brand of dado stack (Forrest, Freud and others).

Then I just plane down the mating piece on both sides to sneak up on a perfect fit. Make sure you set your plane to make the finest shaving possible, and this should work for you.

— CS

Stop Bridging Your Screws When Using Butt Joints

There definitely are ways to improve your butt joints if you find gaps appearing. Screws and biscuits – used correctly – can make the joint tighter and more durable if you know how to use them.

While dovetails and mortise-and-tenon joints are excellent options, we know that a lot of woodworkers use screws to simply pull butt joints tight. There’s nothing wrong with that, but using the correct screws and techniques will ensure that your joint actually is tight.

Many woodworkers are using sheet-metal and drywall screws to assemble projects. These will work, but there’s a reason woodworking screws exist.

The thread-free part of a wood screw shank (under the screw head) allows the threads to bite into the second wood piece, while the first piece (the one being attached) is able to pull tight against it. If there are threads over the entire length of the screw shank, the threads will bite into the wood in the attaching piece and will stop the first piece from seating tight when the screw head reaches the wood surface. This is something called “bridging,” and you’ll never get a tight joint.

The trick to a tight butt joint is drilling a proper clearance hole before you drive in a sheet-metal screw. The clearance hole prevents the threads from catching in the top piece.

Using a standard wood screw with a partially-threaded shank will solve this, or you can make sure the clearance hole in the attaching piece is large enough to keep the threads from catching in the wood. Either way, your joint will end up tight and solid.

— David Thiel

Improve Butt Joints with Pocket-hole Screws, Biscuits

We like pocket-hole screws to build utility cabinets and frames because no other joint is as fast or requires as little clamping.

But there is one downside with pocket-hole screws when you are joining a shelf, top or bottom to a side. It can be quite difficult to hold the shelf in perfect position as you drive the screws home. If the piece shifts even the slightest bit, you’ll have a shelf that is cockeyed with an ugly, obvious gap on one side.

To get around this, we combine biscuits and pocket-hole screws to get the best of both worlds. The extra time the biscuits take is minimal. First, cut your biscuit slots in your shelf and side piece. Then cut the pocket holes in the underside of the shelf.

Put glue and biscuits in the biscuit slots and put the shelf in place. Then you can drive the pocket-hole screws home. Why do we like this method so much? Well, there are three reasons:

• The biscuits hold the shelf in place as you drive the screws so it cannot shift and your case will be perfectly square.

• The pocket-hole screws hold the shelf and side pieces together as the glue dries. This is especially helpful with the middle part of the shelf, which is difficult to clamp if you use only biscuits. The pocket-hole screws pull the pieces together across the shelf without a single clamp.

• If you are a cheapskate, you can remove the screws once the glue is dry and reuse them.

— CS

Biscuits keep the shelf aligned vertically and the pocket-hole screws help clamp the middle of the panel. Add some glue, cinch the screws down tight and you’re done – it’s that easy. And here’s the best part: No clamps required.

The Best Way to Clamp Miters in Casework

Joining your cabinet’s sides and face frame with a miter is a classy way to dress up an ordinary box – and it is a signature of contemporary furniture design. But accomplishing this joint without an ugly gap somewhere along that miter is another story.

Many people spend lots of money on corner clamps and clamping jigs. Or they construct convoluted cauls. My solution is tape. Yes, tape.

I was shown this technique of cutting straight and clean joints and taping them together when I worked in a large production cabinet shop where time was money. I’ve used this technique on mitered joints that were 10’ long and it worked flawlessly. It also works great for gluing compound miters.

To cut a clean miter using your table saw, set the blade to 45° and clamp an accessory fence to your saw’s rip fence. The accessory fence should be made using a softer wood, such as poplar or pine. A harder wood will ruin the sharp tip of your miter. Raise the blade while it is spinning until it kisses the accessory fence. Now you can cut your miters.

The real trick to dead-on miters is how you glue them. As shown in the photos, tape the outside of the joint together, spread glue on the joint and then fold the parts to assemble things. Band clamps or more tape will hold the parts together as they dry.

— Jim Stack

When taping your miters, lay the parts face up so the mitered edges are touching. Then tape the joint with clear packing tape.

Next fold the assembly and use tape to hold it square until the glue sets.