I honestly think biscuit jointing with router bits is one of those woodworking hacks that doesn't get nearly enough love from hobbyists. Most people assume that if you want to use biscuits to align your tabletop or strengthen a miter, you have to run out and drop a couple hundred bucks on a dedicated plate joiner. While those machines are great, they're basically one-trick ponies that take up a lot of shelf space. If you already have a handheld router, you're halfway there.
It's one of those techniques that feels a bit intimidating the first time you try it, mostly because you're spinning a sharp wing-cutter at 20,000 RPMs, but once you get the hang of the setup, it's incredibly satisfying. It's fast, it's accurate, and it saves you from having a "tool for everything" cluttering up your garage.
Why Bother Using a Router for Biscuits?
Let's be real: space and money are usually the biggest hurdles in any shop. If you're only doing a few projects a year that require biscuit joints, buying a dedicated biscuit joiner is hard to justify. A router is already a versatile beast. By just adding a specific slot-cutting bit, you turn that router into a precision joining machine.
Another big plus is the clean cut. Dedicated biscuit joiners use a circular saw-style blade that plunges forward. They're fast, but they can occasionally "walk" or skip if you aren't holding them perfectly. A router, especially if it has a nice wide base, feels a bit more stable for some people. You're moving the tool along the edge of the wood, which can feel more controlled than the plunging motion of a dedicated machine.
The Essential Gear You'll Need
To get started with biscuit jointing with router setups, you can't just use any old bit. You're going to need a 5/32-inch slot-cutting bit. This is the standard width for the most common biscuits (sizes #0, #10, and #20). These bits usually look like a little three or four-wing flywheel with a bearing in the center.
The bearing is the "secret sauce" here. It acts as a depth stop. When the bearing hits the edge of your wood, it prevents the cutter from going any deeper. This ensures that every single slot you cut is the exact same depth, which is crucial if you want your boards to actually line up. You'll also want a router with a decent-sized baseplate. A small trim router can do it, but a mid-sized fixed-base or plunge router gives you more surface area to keep the tool flat against the wood.
Setting Up Your Workspace
Before you even touch the power switch, you've got to get your boards prepped. Layout is where most people mess up. I usually lay my boards out exactly how I want them to look in the finished piece—matching the grain, checking for bows, and deciding which side is the "show" side.
Once I'm happy with the layout, I draw a single line across the seam where each biscuit is going to go. Don't worry about being surgical with the measurement between biscuits; usually, 6 to 8 inches apart is plenty. The main thing is that the line crosses both boards at the exact same point. This line tells you exactly where to center your router bit.
One thing I've learned the hard way: always mark the "up" side of your boards. Even if you think your router bit is perfectly centered in the thickness of the wood, it probably isn't. By always referencing the router base from the same face of the wood (the top), even if the slot is a millimeter off-center, the boards will still sit perfectly flush when you put them together.
The Technique: Making the Cut
Now for the actual work. You'll want to clamp your workpiece down firmly to your workbench. If the board moves while you're cutting, you're going to end up with a sloppy slot, and that defeats the whole purpose of using biscuits for alignment.
When you're biscuit jointing with router tools, you don't just plunge the bit in and pull it out. You'll want to start the router, let it get up to full speed, and then gently ease the cutter into the wood at your pencil mark. I usually slide the router side-to-side just a tiny bit—maybe a quarter-inch total—to give the biscuit a little room to breathe.
Biscuits are designed to swell when they hit wood glue, so the fit doesn't need to be airtight right out of the gate. In fact, having a little lateral wiggle room is a good thing; it allows you to shift the boards slightly left or right during the glue-up to get the ends perfectly flush.
Dealing with Different Biscuit Sizes
Most slot cutters are designed for the #20 biscuit, which is the big boy of the biscuit world. But what if you're working on something smaller, like a picture frame or a thin drawer front? This is where the bearing on your router bit comes into play.
You can actually swap out the bearings on most slot cutters to change how deep the bit goes. A larger bearing means a shallower cut (for #0 biscuits), and a smaller bearing lets the bit bite deeper (for #20s). Most hobbyists stick with #20s for almost everything because they provide the most surface area for glue, but it's nice to know you have options if you're working with thinner stock.
Common Mistakes to Avoid
We've all been there. You finish your cuts, go to dry-fit the boards, and realize something is wonky. The most common culprit is "tipping." If you don't keep the router base perfectly flat on the face of the board, the slot will be cut at a slight angle. When you try to join the boards, they won't sit flat—they'll create a V-shape.
To avoid this, I sometimes clamp a "sacrificial" board of the same thickness right next to the one I'm cutting. This gives the router base a much wider platform to sit on, making it almost impossible to tip.
Another thing to watch out for is sawdust buildup. Those slot-cutting bits can create a lot of fine dust that gets trapped in the slot. If you don't blow the slots out before you add glue and biscuits, the biscuit might not sit deep enough, and you'll be left wondering why your joint won't close.
Glue-Up and Assembly
Once your slots are cut, the rest is pretty straightforward. I like to do a "dry fit" first. No glue, just biscuits. This lets you see if everything aligns and gives you a chance to fix any shallow slots.
When you're ready for the real deal, put a little bit of glue into the slot—not too much, or it'll squeeze out everywhere—and a little on the biscuit itself. Slide them in, join the boards, and get your clamps on. You don't need massive amounts of pressure here; you just need enough to pull the joint tight. The biscuits will do the heavy lifting of keeping the faces aligned while the glue cures.
Is It Better Than a Plate Joiner?
It's not necessarily "better," but it's definitely more accessible. A dedicated plate joiner is faster if you're doing fifty joints a day. It's also easier to use on the ends of narrow boards. But for the average woodworker who builds a table or a bookshelf every few months, biscuit jointing with router bits is more than enough. It's accurate, uses tools you already own, and the results are identical to what you'd get with a $500 setup.
At the end of the day, woodworking is about using what you have to create something solid. Biscuits aren't really about structural strength—they're about alignment. They make the glue-up process ten times less stressful because you aren't fighting with boards sliding around on a film of wet glue. Whether you use a fancy machine or a trusty router, the end result is a flat, professional-looking surface that you can be proud of.
So, next time you're planning a tabletop, skip the expensive new tool and grab a slot-cutter bit. It takes a little more setup, but the satisfaction of a perfectly flush joint is well worth the extra few minutes of prep.