Wood Slot Cutting Machine

This article is from Issue 68 of Woodcraft Magazine.

Create stronger corners by partnering your tablesaw or router with one of these simple splining jigs

PRIMARY USES

This is the Great Planes Slot Machine Hinge Slotting Tool. This motorized hinge slot cutter will do that ugly task in a matter of seconds. This has a one-year warranty. The Slot Machine works far better than a hobby knife for making slots in thin balsa and fragile structures because you do not have to push so hard while cutting. Cutting Edge Design: Electronic Cutting Machines Cut, craft, and create on a whole new level with the precise power with our Electronic Cutting Machines, essential for those destined to DIY. Browse our selection of electronic cutting machine models below and start shopping today!

Perfect slots Drilling end holes and sawing out the waste between them is one way to form a slot. But success depends on your unwavering ability to follow the straight cutlines connecting the end holes with a scrollsaw or jigsaw.

Providing registration and mechanical reinforcement to mitered corners in frames, small boxes, and large cases.

The trouble with a basic miter joint is that it’s more beautiful than brawny. On its own, an end grain-to-end grain glue joint is inherently weak. It needs backup.

Enter the spline. Inserting a strip of wood, plywood, or other material (such as hardboard), into slots cut on the miter’s opposing faces reinforces the joint and helps keep parts aligned during assembly.

These days, the biscuit joiner is the go-to tool for splining, but there are better ways to skin (or spline) the cat. By using your tablesaw or router, you can make full-width splines that can add strength and detail to your design. Investing a little time to make the trio of jigs shown here will expand your joint-making repertoire by enabling you to produce perfect spline slots with either machine.

Making the Cut – Blade or Bit?

Spline slots can be cut with either a blade or bit, but a flat-bottomed cut is essential for a clean-looking joint. Here’s what you’ll need to get started.

Tablesaw: Several manufacturers offer special flat-topped, joinery-grade FTG blades for around $150, but a good ATBR (Alternating Top Bevel with Raker) blade can get the job done for about $70.

Router: Slot-cutting bits range from $30 for a single, fixed-width cutter, to $80 for a multi-cutter set. Cutters are available in widths as thin as 1⁄16', an advantage for small projects. Bearing-guided bits permit you to take the tool to the work, but even with larger bits, the slot depth will max out at 1⁄2'.

Twin-Faced Tablesaw Jig for Splining Frames

When cutting spline slots, a standard tenoning jig is ineffective because it demands that half the slots must be cut with the workpiece’s show face against the jig, and half with it facing away. If the slot isn’t perfectly centered, the spline joint will be misaligned.

Designed to straddle the rip fence, this twin-faced jig ensures perfect slot alignment, even when making offset slots. A 4 × 7' hold-down board keeps the workpiece from sliding and serves as a backer when slotting the right-hand miters.

Set up the first slot. Position the right-hand miter against the face panel show face out, and clamp the hold-down to the jig. Slot all of your right-hand miters before changing the setup. (To eliminate the chance of overcutting the slot on the return stroke, remove the workpiece before retracting the jig.)

Block prevents blowout. To set the jig to make the left-hand miter slots, simply turn the jig around on the fence. Positioning the hold-down so that it covers the top end of the slot ensures a clean exit.

Aligned splines. Again with the show face out, cut the slots on the remaining (left-hand) miters. After cutting the slots, cut the spline to fit.

A Simple Sled for Table-Routed Frames

A router table splining sled may not be as versatile as its tablesaw counterpart, but this jig is well suited for smaller workpieces, and easy to knock together when the need arises. Superior to a simple angled pushblock, the plywood base registers against both fences, eliminating the chance of tipping your workpiece into the bit. In addition, the fence-mounted clamp fixes the work against the fence to prevent tearout.

Finish with your left. To ready the jig to rout the left-hand miter slots, rotate the sled and reposition the toggle clamp. The clamp’s vertical locking handle allows you to put clamping pressure closer to the cut.

A Multipurpose Jig for Case Miters

When cutting spline slots on wide case pieces at the tablesaw, you may be able to set the saw blade perpendicular to the face of the miter, lay the work flat on the table, and push the panel over the blade. For smaller pieces however, a jig can be a big help.

What makes this jig worth building is that it can be outfitted to work at the tablesaw or router table. In either operation, the jig registers the workpiece solidly on the face of the miter, instead of on its crushable tip.

Mitering and splining at the tablesaw.

One big advantage to using this jig at the tablesaw is that it enables you to cut both miters and spline slots without fussing with your blade’s bevel angle.

After mitering, simply flip the stock so that the opposite face rests on the ramp, lower the blade and adjust the rip fence. For strength, position the slot close to the inside edge, or root, of the miter.

Two ways to rout splines.

With minor modifications, this jig can rout spline slots in both large and small case pieces on the router table. Attaching a stop to the ramp turns the jig into an angled sled. Adding an auxiliary panel to the ramp and clamping the base to the router table creates a chute that can help keep long mitered edges registered against the router table’s fence.

Splines–Simple or Strong?

Woodworkers will agree that a properly-sized spline should fit snugly, while allowing the joint to close completely. How to cut the strips seems to be a source of some debate.

For maximum strength, a spline’s face grain should run perpendicular to the face of the miter. To do this, use a tenoning jig and slice the strips from a piece of stock that’s been dressed flat and squared on both ends. Then, saw them to length using a miter gauge and stopblock.

To simplify spline making, some settle with ripped strips. Ripped strips offer registration, but they are more likely to snap if roughly handled. If your project requires long splines and you’re pressed for time, consider sizing the slot to fit a plywood spline. If the joint is visible, cap the ends of the slots with solid wood.

This article is from Issue 21 of Woodcraft Magazine.

Because biscuit joints are easy to mark out and quick to cut, using one almost seems like cheating. In truth, biscuits may not be as strong as some traditional types of joinery and may not be suitable for heavy-duty loads, but they’re perfect for plenty of projects. Woodworkers and carpenters have been employing biscuits to successfully solve all sorts of assembly and alignment problems for over two decades. The easiest way to appreciate their versatility and strengths is by putting them to use.

The safest way to cut biscuit slots is with a biscuit joiner. This tool is designed to do nothing but plunge-cut arc-shaped slots. (Unlike the router/biscuit-cutting bit combo, the biscuit joiner’s cutter retracts inside the tool as you pull it away from your work.) From there, a flat, football-shaped piece of compressed wood, called a biscuit, fits into a pair of matching slots.

What makes biscuits better than dowels? The size and shape of the slot. The oversized slot lets the biscuit move slightly, enabling you to tweak parts into perfect alignment. However, once glued, the biscuits swell and lock the parts in place.

Diy Cnc Wood Cutting Machines

You can master basic biscuit joiner use in five minutes, but you will continue to learn new tricks with each project. Following are some common joints that you can practice making to familiarize yourself with a new tool or get better reacquainted with your old workhorse.

begin with the two slot test

A biscuit joiner should cut a slot slightly deeper than half the width of the biscuit you’re trying to fit. This space provides some wiggle room, but still ensures that about half remains on each side of the joint. Here’s how to check your joiner’s depth setting. First, make a test slot. Next, stick in a biscuit and mark a pencil line where the biscuit touches the wood, as shown in Photo 1. Now flip the biscuit and mark a second line. Adjust the depth-setting dial on your tool so that overlap is about 1/8', as shown in Photo 2.

THE face-TO-edge BISCUIT JOINT

To cut the biscuit slots for the shelf, draw a pencil line across the inside face of the side and clamp the edge of the shelf against the line. Next, mark your biscuit slot marks on the top of the shelf. Resting the biscuit joiner on its base, place it on the side and cut the slot for the shelf as in Photo C. The base also serves as your reference when slotting the sides. Turn the joiner on its head, use the line engraved on the bottom of the tool to align it with your slot marks, and plunge it into the side, Photo D. Once cut, insert biscuits into the grooves and flip the shelf up on the location line.

Stick the board’s end over the edge of your bench so that the fence, not the tool’s base, sets the slot depth.

Balance the biscuit joiner’s fence on the end of the side panel to cut the grooves in the face.

Face-to-edge joints are the bread-and-butter joint for biscuit joiners. A biscuit joiner can cut the needed joints to assemble a cabinet in about as much time as it takes to drag a heavy sheet of MDF to your table saw.

Building a simple box provides a good opportunity to explore the advantages and disadvantages of fence- or base-guided slot cutting. Sometimes, you’ll have the freedom to choose the method, but sometimes the decision is made for you. Box-making uses both.

First, position the side and end panels together and draw lines across the joint to mark where you want a biscuit. (As a rule of thumb, place the biscuits about 6' apart.) When you pull the panels apart, you should see marks on the edges and ends.

To cut the grooves in the edge of the end panel, place the work flat on the workbench, as shown in Photo A. Adjust the fence so that the blade cuts a slot roughly through the center of your work. To cut the face grooves in the side, you’ll balance the fence on the panel’s edge as shown in Photo B.

Remove or retract the fence and use the joiner’s base to cut the slots in the end of the shelf.

Don’t move your wood; just flip your joiner so that the base rides against the shelf. Plunge the joiner into the side.

Biscuit Sizes

To cut grooves for most of the biscuit sizes (0, 10, 20), simply adjust the stop on your biscuit joiner. Smaller FF (or face frame) biscuits are available for the Porter-Cable biscuit joiner. To use these mini biscuits, you’ll need to switch out the standard 4' dia. cutter with a smaller 2' dia. blade.

THE END-TO-EDGE AND MITERED BISCUIT JOINTS

Biscuits are also an easy way to build mitered and end-to-edge frames that you would use for picture frames or for a cabinet’s face frame. In this case, biscuits are very useful because they are adding reinforcement to otherwise weak end-grain joints.

Start by selecting the right biscuit. An easy way to do this is to position the joint together then arrange one or more biscuits on top. Drawing a center line on a test biscuit can help you lay out the slots as shown in Photo E. Wider biscuits provide more strength (even if you saw off an end), but there are times when you want the biscuit to be hidden within the joint. When form is as important as function, use the Biscuit Sizing Chart on page 13. When picking a biscuit, don’t forget the wiggle room. The slot is usually about 3/16' wider than the biscuit you’re trying to fit.

When slotting narrow pieces, don’t hand-hold the stock. Because a portion of the blade will be exposed while making the cut, and since the spinning blade can “walk” if the tool or work isn’t properly held in place, it’s too easy to get hurt. Eliminating the risk of a visit to the ER is easy: simply clamp narrow pieces to a stopblock as shown in Photo F.

You can now align the center mark on the joiner with the marks on your stock and make the cut. After making the cuts, glue the biscuits into their slots and clamp the frame together. Once the glue has dried, you can slice off the protruding biscuit tip as in Photo G.

Position the bigger biscuit so that it won’t protrude into the visible inside edge of the frame.

Use clamps and extra backup, not your free hand, when cutting narrow stock.

Saw off the biscuit tip with a handsaw or using your table saw and crosscut sled.

Double-Biscuit Joinery

Biscuits don’t fare well when matched against other joints in wood-joint torture tests. Because biscuits are relatively short, it doesn’t take a rocket scientist to realize that this joint isn’t as strong as traditional mortise-and-tenon or half-lap joints.

An easy way to strengthen a biscuit joint is to cut two grooves, as shown at right. In seconds, you’ve doubled the gluing area of the joint. Try to leave a ¼'- to ½'-strip of wood between the biscuits to maximize available gluing surfaces and preserve the strength of the wood. (With careful spacing, you can use the double-biscuit technique on a ¾'-thick rail and stile joint.)

To cut the grooves, I prefer to use spacers instead of my fence. Referencing the joiner and working against my bench is fast, and for those times when I forget to cut a slot, easily repeatable.

face miters

Face miters are A way to hide end-and edge-grain when making solid wood boxes or plywood cabinets, but long miters are tough to glue and tricky to reinforce. A few biscuits can solve both problems. They can register the ends so that the corners can’t slip during clamp-up and strengthen the otherwise end-grain joint. A biscuit-reinforced miter is as strong as a full table saw-cut spline, but biscuits can be hidden within the miter for a cleaner-looking joint. (With the table saw, you cut the spline from edge to edge.)

To cut a slot in an angled edge, use your fence. How you cut the slots in the mitered face depends on the fence-adjustment flexibility of your biscuit joiner and your working style. If your router has a fixed fence (or if you prefer working with your workpiece flat against your bench) you will want to try making your cuts as shown in Photo H. Set your fence to 45°, adjust the cutter depth so that it doesn’t slice through the thinner tip of your miter, and make a plunge cut into the end.

Some joiners, like the Porter-Cable 557 (see the Buying Guide) have a two-stage fence that can reference the outer face of the miter as shown in Photo I. This design prevents corner alignment problems, especially if the stock thicknesses aren’t equal. The wrap-around style of this fence also makes it easier to hold the tool in place while making the cut.

Adjust the fence height or add a shim so that the blade does not cut through the tip of the miter.

When the fence is set to 135°, you can squeeze the joiner against the miter as you cut the biscuit slot.

offset joinery

There are times, as when joining a rail to a leg where you may not want a flush-fitting joint. Your biscuit joinser is equally adept at creating offsets. The trick is to use a spacer that the same thickness as your desired step back. The spacer-offset trick can be used with your biscuit joiner’s fence, or under the base of the tool, as shown here. (I think resting the joiner on top of a large hardboard spacer is alot easier than trying to sandwich the spacer between the work and biscuit joiner’s fence.)

Wood Die Cutting Machine

To make the offset joint, mark the leg and apron for the biscuit slot just as before. Now choose a spacer that is the same thickness as your desired offset.

Wood And Metal Cutting Machine

Position the spacer under the jointer as shown in Photo J, position the leg with the show face against the bench and cut the slot. To cut the matching slot in the apron, simply remove the spacer and slot the end of the board as shown in Photo K. Be sure the show face is touching the bench.

Wood Slot Cutting Machine Tools

THE EDGE-TO-EDGE BISCUIT JOINT

You might want to think twice before using biscuits for solid-wood edge joints (See “Biscuits or No Biscuits?”). but biscuits are very useful for attaching solid wood edging to sheet goods, and also when you need to straighten out bowed boards. With practice, you may be able to biscuit an edge joint in less time than it takes to read how it’s done.

To start, position the boards edge-to-edge, then make short pencil lines across the joints about every 8' for the slots, as shown in Photo L. Make the first and last slots at least 3' in from the end; that way, you won’t accidentally expose a biscuit if you trim the panel later.

Next, set the joiner’s fence height to cut a slot roughly in the center of the board. To ensure that the joiner’s fence is setting the slot height, and not the base, clamp the board so that the edge sticks off your bench as shown in Photo M. Let the cutter reach full speed before plunging it into the wood.

Wood Slot Cutting Machine Software

You’re now ready for glue-up. Because the biscuits swell quickly, do a dry assembly and make sure everything’s set before you open the glue bottle (Photo N). Remove any sawdust from the slots, test-fit your biscuits, and dry-assemble the panel. If everything fits like it should, you’re set to reassemble it for good with glue.

Cnc Wood Cutting Machines

Keep the fence flat on the board surface when cutting slots.

Use a biscuit-slot bottle to quickly squeeze glue into the slots.