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2 Ways to Cut a 3-Way Miter

2 Ways to Cut a 3-Way Miter

Create this impressive joint by hand or with power tools.

By Garrett Glaser

 

Admiring the complex 3-way mitered joint between the leg and aprons in an antique Chinese table is natural. But the thought of cutting and fitting this interlocking joint by hand is enough to make most woodworkers run up a white flag. Fortunately, the same joint appears in contemporary designs, which means there’s also a modern (easier) way to complete it. In this story I’ll demonstrate both methods and provide all the information you need to build a table with 3-way miters. Whether you love the challenge of using hand tools or love the reliability and predictability of modern power tools, there’s a straightforward way to fashion this elegant, versatile and time-tested joint.

 

 

Machine-Cut 3-Way Miter Joint

 

Simplicity defines this joint, because the cuts on all three parts are identical. Each part has two miters and two slots for loose tenons. Only two setups are required, one for mitering and one for routing. This method is based on a miter saw, but a tablesaw can also be used. A simple shopmade jig is used for routing.

The miters must be precise, so a saw that cuts accurately is a must. Set up the saw to make a perfectly plumb 45˚ cut. Don’t rely on the saw’s scales—if the miters are off by even a tiny amount, the joints won’t close tightly. Make test cuts on scrap stock to ensure accuracy.

Start with straight, square stock. Crosscut both ends at 90˚, about 1" longer than final dimension. Mark the final length on each piece; mark both ends of the apron blanks. Set aside a 12" length of the same stock for layout. Mark a registration line on the layout piece about 4" from one end. Clamp this piece to the saw and cut a 45˚ miter. Without moving the layout piece, transfer the registration line to the saw’s fence (Photo 1). Remove the layout piece and position it next to a leg blank so the tip of its miter aligns with the final length mark (Photo 2). Transfer the registration line to the leg and continue it around all four sides. Mark every blank this way—mark both ends of the apron blanks.

Cut miters on two adjacent faces of each blank. Align the registration lines on the blank and the saw before making each cut (Photo 3). To minimize tearout, orient the blank so that the second miter is always made with the first miter facing up. If the cuts don’t meet exactly at a point on the inside corner, something is awry—check the saw’s setup. When mitering the aprons, make sure that the pointed ends of the miters are on the same edge!

Loose tenons reinforce all the miters. Rout mortises for the loose tenons using a 3/8" straight bit, a 1/2" guide bushing and a simple jig (Fig. A, below). Use one end of the jig to rout the left facet of each joint and the other end to rout the right facet (Photo 4). Square the end of the mortises with a chisel. Then make loose tenons to fit the slots.

As all of the joints are interrelated, it’s best to check the way they fit with the table assembled. A positioning jig and a band clamp stabilize the pieces during this process (Photo 5). The jig positions the legs and keeps them plumb; the clamp equalizes pressure on the joints. To make the jig, cut a piece of MDF to match the table’s footprint (it’s defined by the lengths of the short and long aprons). Position the legs flush with the corners. Press corner blocks against both inside edges of each leg. Then fasten the blocks to the MDF.

With the table assembled, examine the joints and mark surfaces that need finessing. Then true each joint in stages, round-robin-style, using a rabbeting plane, a chisel or even a sanding block. Keep a couple of bar clamps handy to strategically apply additional clamping pressure. If you need to apply downward pressure on the aprons, raise the jig on blocks to provide a clamping lip.

When the joints fit satisfactorily, disassemble the table. Apply glue to the legs and short aprons and install the appropriate loose tenons. Assemble the ends and clamp them in the positioning jig. Apply glue to the remaining joint surfaces and install the remaining tenons. Spread the end assemblies to install the long aprons. Then install the band clamp and any necessary “tweaking” clamps.


Fig. A: Routing Jig

Click any image to view a larger version.

1. Use a scrap piece marked with a registration line to set up the saw. Clamp the piece to the saw and miter the end. Then without moving the piece, transfer the registration line to the saw.


2. Use the mitered scrap piece to mark all the blanks. Align the tip of its miter with a line drawn on the blank to indicate its final length. Then transfer the registration line.


3. Align the registration lines to cut miters on adjacent faces of all the leg and apron blanks. To minimize tearout, always cut the second miter with the first miter facing up.


4. Rout slots for loose tenons with a straight bit, a guide bushing and a simple jig. Square the slot ends by hand. Then cut loose tenons to fit.


5. Assemble the table using a jig to keep the legs in position. Install the short aprons and tenons. Spread the ends to install the long aprons. Then use a band clamp to draw the joints tight.

 

 

Hand-Cut 3-Way Miter Joint

 

Most traditional Chinese 3-way miter joints consist of three (or more) interlocking pieces, each with their own configuration of tenons and mortises. I’ve created a simplified version that requires only two pieces, the leg and two identical but mirror-image aprons. My joint won’t win awards for authentic traditional joinery, but it’s a good jumping-off point. Mastering this joint develops skills that will allow you to tackle more complex versions. A good place to start looking for authentic examples is Gustav Ecke’s excellent book Chinese Domestic Furniture (see Source, below).

Creating a 3-way miter by hand requires three skills: precise layout, sawing straight lines (see “Using a Pull Saw,” below) and accurately removing waste. No single step is especially difficult, but there are a good number of them. The order in which you complete the steps is the key to success. A fourth requirement isn’t so much a skill as a personality trait: patience. Mastering this process takes practice.

Start by milling the stock. Use light-colored wood at first, so your layout lines will be easy to see and imperfections will show clearly as dark crevices in the assembled joints. In 3-way miters, the aprons and legs are squared to the same dimensions. Every piece must be straight. If one piece has a twist or bend, it won’t matter how masterfully you cut and chisel—the joint will never close tightly.

Cut the aprons and legs to final length—the aprons on opposite sides must be identical (or all four aprons, if the table is square). Lay out all of the cuts on the top and all four faces of each leg (Fig. B). Use an accurate square and a sharp pencil or a knife to create the lines.

 

The Leg Joint

The first cuts on each leg are diagonal and stopped (Photo 1 and Fig. C). The two diagonal cuts on the outside faces are the most visible of all the cuts you will make, so use a metal straightedge to ensure clean, straight cuts. Position the straightedge so the blade will split the layout line. Hold the saw against the straightedge and flat on the workpiece. Then saw a groove just deep enough to keep the saw from jumping out as you complete the cut. Remove the straightedge. Keep the blade in the groove while using its heel to make a perpendicular cut down the adjacent side to the first stop line. Then slowly angle the blade forward and use its toe to cut down to the stop line on the opposite side.

The second cuts run across the leg’s two inside faces (Photo 2 and Fig. D). They’re the only cuts that aren’t perpendicular to the surface. Use one of the diagonal cuts you just made to position your saw at the correct angle, then saw back across the face to the diagonal cut on the opposite side.

The third cuts form a tic-tac-toe grid across the top (Photo 3 and Fig. E). Although most of these cuts will be removed later, making them now ensures square tenons, because it’s much harder to cut a perfectly true short line than a long one. These stopped cuts also act as a guide for waste removal.

The fourth cuts create shoulders for the miter joints (Photo 4 and Fig. F). Establish a straight, shallow groove and then saw diagonally until you reach the outside edge of the top and the bottom edge of the miter on the adjacent face. If the triangular waste piece doesn’t come loose, make sure the diagonal cut was sawed to a uniform depth—rocking the saw from heel to toe sometimes leaves a high spot in the middle.

The fifth cuts remove waste and reveal angled shoulders on the inside faces (Photo 5 and Fig. G). Make a pair of deep stopped cuts that run across the top and down both adjacent faces. Be careful not to cut into the mitered shoulders on the outside faces, as doing so will leave a visible mark when the joint is assembled.

The final cut establishes the flat shoulder at the base of the tenons (Photo 6 and Fig. H). Start by marking guide lines on both inside faces, 5/16" down from the top and running from the inside corner to the saw kerf that defines the tenon cheek. Use the lines to cut diagonally to the kerfs—be sure to stop before you saw into the tenons!

Use a 1/4" Forstner bit to remove as much of the waste as you can (Photo 7). Then switch to a chisel (Photo 8). The shoulder’s surface must be absolutely flat, so finish by paring across the grain. Be sure to remove any ragged fibers left in the corners.

 

The Apron Joint

Mark the aprons for cutting and mortising (Fig. J). The first cuts create miters on the top and outside faces (Photo 9). These diagonal cuts are just as visible as those on the leg, so start them the same way, using a straightedge. Use the heel of the blade to saw the line on the adjacent face and finish the cut by sawing at a 45˚ angle.

Cut the mortise in the top face. (Each apron joint houses one of the leg tenons.) Drill a 3/8" deep hole with a 1/4" Forstner bit and then square the corners with a chisel (Photo 10).

Draw guide lines on the two mitered faces on the inside of the joint (Fig. J). One line is located 5/16" from the outside edge and the other 5/16" from the bottom of the miter—these lines align with the mortise on two sides.

When removing the waste, use one line to guide the side of the chisel and the other to establish the depth (Photo 11). Barely tap the chisel for the first cuts—the grain is so short at the front that it’s easy to remove too much. You should be left with one relatively clean end-grain shoulder and two fairly ragged long-grain shoulders. Make sure the end-grain shoulder is absolutely flat. Pare the long-grain shoulders to exactly 5/16" thickness (Photo 12).

 

True the fit

When you first assemble a leg and apron, don’t be alarmed if the pieces don’t even go together. Truing the fit requires patience and thoughtful sleuthing. Look carefully to determine what might be gumming up the works (Photo 13). Make sure the mortise fits the tenon without binding—if this joint is too tight it can keep the other parts of the joint from fitting. Once the mortise and tenon fit properly, check the other joint surfaces for irregularities.

Don’t spend too much time fitting an apron and leg before adding the second apron. After all, this is a three-piece joint, and having all three parts together shows much more than two parts can show. You’ll quickly learn how a small adjustment on one piece can affect the way the other two pieces fit.

In fact, because all the joints are interrelated, the best strategy is to assemble the legs and aprons as soon as possible and true each joint in stages, roundrobin- style, using a rabbet plane and a chisel (Photo 14). Use the positioning jig shown earlier to keep the legs plumb while you finesse the joints. Temporarily shimming the mortises during this process can help to identify problem areas. Once all the joints have been fit, you’ll probably have to permanently shim some of the mortises. That’s OK; the shims will be virtually invisible after they’re glued and sanded flush.

Use the assembly jig and the band clamp for glueup. If you need to apply downward pressure on the aprons, raise the jig on blocks to provide a clamping lip.


Fig. B: Leg Layout


Fig. C: First Cuts


Fig. D: Second Cuts


Fig. E: Third Cuts


Fig. F: Fourth Cuts


Fig. G: Fifth Cuts


Fig. H: Final Cut


Fig. J: Apron Layout

1. Start by sawing four diagonals on each leg, one on each face. Use a straightedge to guide the saw. Attach sandpaper to the back of the straightedge so it won’t slip.


2. Saw the bottom edge of the miter on the two inside faces. Use the diagonal kerf from the previous step to establish the 45˚ slope. Then work back to the diagonal kerf on the opposite edge.


3. Create the tic-tac-toe grid on the top by making four straight cuts. Saw to the upper layout lines on the adjacent faces.


4. Create square shoulders on the two outside miters by sawing diagonally across the top and one adjacent face. Waste removal begins with these cuts.


5. Make deep stopped cuts across both inside faces to reveal the angled inside shoulders. You’ll have to re-mark some of the layout lines in order to make these cuts.


6. Complete each leg joint by removing the waste from around the two tenons. Sawing across the inside corner to the tenon kerfs creates a flat shoulder at the base of the tenons.


7. Remove the bulk of the waste that remains between the tenons by drilling through the tic-tac-toe blocks.


8. Complete the joint by paring across the grain to create a flat shoulder beneath the tenons.


9. Start each apron corner by making two through diagonal cuts, one on the top and one on the outside face.


10. Square the mortise after drilling a stopped hole to remove most of the waste.


11. Hollow the inside of the joint after marking the shoulders on both mitered faces. Remove the waste with a series of shallow chisel cuts, working from front to back.


12. Pare to the guide lines and square the end-grain shoulder. Removing the waste reveals the mortise—it’s flush with the corner formed by the end-grain and long-grain shoulders.


13. Fitting the joints takes time. Make sure that the shoulders of each joint are the same thickness, that all of the mating surfaces are absolutely flat and that the mortises aren’t too small.


14. All of the joints are interrelated, so assemble the table as soon as you can. Then work a little on each joint in rotation. Here, a temporary shim shows high spots that require further work.

 

 

Using a Pull Saw

The art of sawing straight and square with a pull saw isn’t as mysterious as you might think. I use a fine-tooth flush-cut pull saw to cut 3-way miters. (The teeth on a flush-cut saw have no set, which means they don’t flare beyond the body of the blade). You can spend a lot of money for this type of saw, but I get great results using a $10 version from a home improvement store—and I don’t have to worry about the replacement cost if I kink the blade or break a tooth.

When you saw, the goal is to split the layout line. Don’t worry—it’s easier than it sounds. Just make sure that the outside edge of the blade follows the center of the line, so half of the line remains on the workpiece and the other half becomes sawdust.

To make a through cut, you follow two adjacent lines, one across the top of the piece and one continuing down the side that faces you. Focus first on the top line. Hold the blade nearly parallel to the surface, but with the heel (the end closest to the handle) raised slightly, and saw lightly along the line from the far side to the near side until you’ve made a shallow groove across the top. Keep the saw in the groove and switch your focus to the vertical line on the side. Using the heel of the blade, saw your way down the line until the teeth of your saw meet the ends of both lines. If you are cutting square stock, this puts your saw at a 45˚angle. Keep your saw at this angle to complete the cut. The kerf you’ve created keeps the saw square and plumb for the rest of the cut.

To make a stopped cut you need three lines—the line across the top and stopped lines on the opposite adjacent faces. Begin the cut as you would a through cut, creating a groove across the top and then cutting with the heel to the bottom of the first stopped line. But instead of putting pressure on the heel to continue the cut, make the toe of the saw do all the work, cutting down the line on the opposite face, slowly leveling the blade so that the teeth connect the two points where the cut should stop.

 

Build a Table with 3-Way Miter Joints

The legs and aprons of tables joined with 3-way miters form an open frame whose dimensions are determined by the lengths of the three components. Adding a top can be as simple as attaching cleats inside the aprons and cutting a piece to fit.

 

Cutting List

 

Source

Note: Product availability and prices are subject to change.

Tools for Working Wood, toolsforworkingwood.com, 800-426-4613; Gustav Ecke, Chinese Domestic Furniture, Mineola: Dover Publications, 1986, AQ-1037.


This story originally appeared in American Woodworker December/January 2011, issue #151.

 

 

 

Lock Miters

Lock Miters

This simple set-up process guarantees perfect joints!

By George Vondriska


Lock miters are strong, attractive joints that make assembly easy. So why the heck don’t we use lock miters more? I think it’s because they can be a pain to set up.Well,no more excuses.Here’s a clever technique, sent to us by Jim Rodgers of Martinez,California. Give it a try and you may become a lock miter enthusiast.

 

What’s a lock miter?

A lock miter router bit cuts a 45-degree miter with a tongue and groove. When correctly cut, the parts go together at a perfect 90-degree angle and the interlocking tongues and grooves make for lots of mechanical strength and glue surface area. Lock miters are also great at keeping parts aligned during assembly.Use this joint on drawers, boxes or even hollow columns like newel posts.You can cut a lock miter on end grain, as shown in our photos, or on the long grain.Almost anyplace you’d use a miter, you can successfully use a lock miter.

 

Tooling up

Lock miter bits come in a range of sizes.The size you use depends on the thicknesses of your wood.Even the smallest lock miter bit makes a substantial cut, so I prefer bits with a 1/2-in. shank. They’re more stable and result in smoother cuts.Expect to pay $50 to $100 for a bit,depending on the size.

Note: The maximum size lock miter bit you can run in a 1-1/2-hp router is the 2-in.diameter.Larger bits must be run in a 2-hp or higher machine.

It is essential that you run these massive cutters at the right speed—about 10,000 rpm. Your router must have variable speeds so you can slow down for these big cutters.

 

The perfect set-up

Follow the sequence shown in Photos 1 through 7 to produce perfect lock miters on your router table.Remember to have on hand the material required for your project plus six test pieces. It’s critical that the test pieces be the same thickness as the project pieces because the bit set up is specific to the thickness of your material. As you get more familiar with the set up procedure you’ll need fewer test pieces.


Lock miter tips

If you follow the steps you’ll be able to cut perfect lock miters. Here are some tips to make it even easier:

Use wide pieces. Your project parts must be cut to the right length before cutting the lock miters, but they can be any width. Leave them 1 in. too wide, and cut them to final width after you’ve done the routing. They’ll be easier to handle, and the “blowout” you get on the back of the cut will be cut off when you machine to final width. If your project calls for narrow pieces, 2 in. to 3 in. wide,machine pieces 6 in. to 7 in. wide and rip them to the size you need.

Use a tall fence. Holding a piece vertically against the fence is a lot easier if the fence is high. Use one that’s about 7-in. tall.

Use a “zero clearance” fence. Having the opening surrounding the bit as small as possible helps prevent your workpiece from slipping into the opening.

Precut your parts. A 2- or 3-hp router will hog all the material off in one pass, but it’s going to be a lot easier to machine the lock miter if you precut your parts on the tablesaw with a 45-degree bevel.Trim off only about 3/8 in. on 3/4-in. stock.

Use push blocks. Neoprene-padded push blocks will make cutting lock miters easier and safer (see Sources, below).

Make a permanent set up piece. When you have all the setup done, machine a piece and keep it for your next project. If you want to set up the whole operation for the same thickness of material again, use the set up piece to set the thickness of your work, the height of the bit and to position the fence.You’ll still need to do some test cuts and some final tweaking, but you’ll be darn close.


Fig. A: Centering the Bit


Fig. B: Fence Position


Sources

(Note: Product availability and costs are subject to change since original publication date.)

Router Bits:

CMT, 888-CMT-BITS

Eagle America, 800-872-2511

Jesada, 800-531-5559

MLCS, 800-533-9298

Whiteside, 800-225-3982

Woodline Arizona, 800-472-6950

 

Push Blocks:

Eagle America, 800-872-2511


This story originally appeared in American Woodworker April 2000, issue #79.

April 2000, issue #79

Purchase this back issue.

Click any image to view a larger version.

A lock miter router bit.


First, center the bit on the material.

1. Center the bit on your workpiece by eye. Be sure your router is unplugged.


2. Adjust the router table fence by eye to its approximate position.Three points must be aligned.The top of the workpiece, the face of the fence and the 45- degree angle of the cutter (Fig. B).This is just a preliminary set up.You’ll perfect the fence position later.


3. Test the height of the router bit by cutting two test pieces. Hold each piece flat on the router table.


4. Assemble the test pieces. When the cutter is perfectly centered, the faces of the two pieces will be aligned.Adjust the bit as needed.You must have the bit centered on the material before you start working on the fence position.


Now, set the test position.

5. Examine the test cuts to determine if the fence is correctly positioned. If the cut looks like A, the cut is too shallow and the fence must be moved back. If the cut looks like B, the cut is too deep and the fence must be moved forward. Adjust the fence until the cut looks like C; producing a perfect knife edge on the cut.


Finally, cut your parts.

6. Machine your parts. One part is held flat on the table.The mating part is held vertically against the fence.


7. Assemble the pieces. Your careful machining will result in perfect-fitting corners.