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Installing Knife Hinges

How to Install Knife Hinges

They’re a sure sign of good craftsmanship, but are almost invisible.

By Brad Holden

 

Small and discreet, knife hinges lend a tidy, refined look to your project. They’re ideal for a small cabinet if you want the hinge hardware to virtually disappear.

Knife hinges are also a hallmark of good craftsmanship. Precisely laying out their mortises takes patience and a steady hand. You’ll be using some classic hand tools, such as a marking knife, a marking gauge and a few sharp chisels. There are no short cuts, and practically no room for adjustment once the mortises are cut.

Don’t let me scare you, though. If you follow the steps outlined below, you really can’t go wrong.

There are two styles of knife hinges: straight and off set. Straight hinges are used for overlay doors. Off set hinges let a door swing out farther than straight hinges, so they’re used for cabinets with inset doors. I’ll be showing you how to install off set hinges.

 

Before you start

All knife hinges are composed of two parts, or “leaves,” that are easy to separate. One leaf is mortised into the top and bottom edges of the cabinet’s door; the mating leaf is mortised into the cabinet itself. It’s extremely difficult to cut the mortises in the cabinet after the cabinet is assembled. Your best bet is to hold off gluing the cabinet together until you’ve completed all the mortising.

Begin by temporarily clamping the cabinet together. Cut the door so that it’s a snug fit in the opening.

Next, determine the size of the gap you’ll want all around the door. This isn’t an arbitrary measurement: It’s determined by the gap between the two leaves of your hinges, which is the thickness of the washer between the leaves. Make shims that are the same thickness as the washer. (I use a stack of cut-up playing cards. The washers on my hinges were three cards thick.)

Carefully cut the door smaller, ending up with gaps that are the same size on all four sides. I use a hand plane when I get close to final size in order to avoid taking off too much wood.

 

Door mortises first

The most accurate way to lay out the mortises is with a marking knife and a marking gauge. Making shallow grooves in the wood, these tools allow you to positively register a chisel in a way that a pencil line cannot.

We’ll start with the door mortises, because the thickness of the door determines the position of the hinge. Clamp the door in a vise at a comfortable working height. Position one leaf of the hinge on the door’s top or bottom edge, so that the hinge is flush with the door’s edge. Using a marking knife, mark the hinge’s end with a short, shallow cut (Photo 1). Locate your knife in the cut, slide a small square against the blade and scribe a line all the way across.

Adjust a mortising gauge to the width of the hinge (Photo 2; see Sources, below). You could also use a marking gauge with a single pin or a single wheel, but you’ll have to re-adjust it for each side of the mortise.

Adjust the gauge’s head so that the mortise will be centered on the door. Test the setting on a piece of scrap the same thickness as your door. When you’ve got the setting right, scribe the mortise’s long sides (Photo 3).

Hold the hinge in place again and mark its off set arm (Photo 4). As before, make a short cut first, then scribe the line using a square.

The best way to remove most of the waste inside the mortise is to use a 1/8” bit in a laminate trimmer or other small router (see Sources). You could chop the mortise with a chisel, but it’s risky. The walls of the mortise are usually very thin and could easily split out. The depth of the mortise should exactly match the thickness of one hinge leaf. To set the bit’s depth of cut, turn your router upside down, set a hinge leaf on the router’s base and slide the leaf against the bit (Photo 5).

Rout the mortise (Photo 6). Clamp boards on both sides of the door to keep your router from wobbling. Extend the boards about 1” past the edge of the door to ensure that the router is steady before you start cutting. Rout freehand, staying about 1/32” inside the lines. You’ll find that a 1/8” bit is very easy to control. Don’t push too hard, though; this bit is fragile.

Clean up the mortise by gradually paring to the layout lines. Use a wide chisel on the long sides to make straight, crisp edges (Photo 7). I use a 1-1/4” butt chisel.

 

Cabinet mortises second

The cabinet is still clamped together, right? The first step in marking the cabinet mortises is the same as marking the door mortises: Begin with one end of the hinge. Here, though, the hinge won’t be flush with the cabinet’s side, because you have to allow for a gap between the door and the cabinet. On my cabinet, the gap is the thickness of three playing cards (the thickness of the washer between the hinge leaves). Place the cards, or whatever shims you’re using, between the hinge and the side of the cabinet (Photo 8). Then mark the opposite end of the hinge, shallow and short at first, followed by a squared line.

If the door is set back from the cabinet’s top and bottom, use a square to measure this distance (Photo 9). (If your door is flush with cabinet’s top, bottom and sides, skip this step.) Slide your mortising gauge’s head further away from the pins by this distance. Test your new setting on scrap to make sure it’s right.

Now you can remove the clamps and disassemble the cabinet. Scribe the mortise’s long sides on the cabinet’s top and bottom (Photo 10). Lay the hinge in place, then mark its opposite end and the off set arm. Scribe these lines, as before, using a square and marking knife. Rout the mortises. Clean them up using a chisel (Photo 11 ).

Next, set the hinge leaves in the cabinet mortises and pre-drill pilot holes for the screws (Photo 12). I use a self-centering bit for this operation to ensure that the holes are perfectly aligned. That’s not so critical for the cabinet mortises, because the hinge is trapped, but centered holes are critical for the door mortises, where the hinge could slide.

If you’re using brass screws, “thread” the pilot holes first with steel screws of the same size, then install the brass screws. Use a screwdriver, not a drill/driver, to avoid stripping out or breaking the screws.

You may want to re-assemble the cabinet one more time, just with clamps, to make sure the door hangs right. (Or if you’re feeling confident, glue it!) Reassemble the hinges by slipping the door leaves back onto the pins of the cabinet leaves (Photo 13).

Lay the cabinet on its back and slide the door onto the hinges (Photo 14). You might need some help here, because you can’t see both hinges at the same time. Once the door is in place, pre-drill pilot holes for the screws, then install the screws (Photo 15).

Stand up the cabinet and check the door’s fit and gaps. Make any necessary adjustments using a hand plane or sanding block.

 

Sources

Note: Product availability and prices are subject to change.

Rockler, rockler.com, 800-279-4441, Micro-Adjustable Rosewood Marking Gauge, #22206.

Freud, freudtools.com, 800-334-4107, 1/8” dia. Double Flute Straight Bit, #04-100.




These stories originally appeared in American Woodworker June/July 2012, issue #160.

Knife hinges go undercover when installed—you can barely see them. They’re perfect for the type of cabinets whose hardware shouldn’t distract from the piece’s design or the beauty of the wood.


1. Lay out the door mortises first. Position one hinge leaf flush with the door’s edge, then scribe across the end of the hinge.


2. Set the pins on a mortising gauge to the width of the leaf.


3. Scribe the mortise from the face side of the door.


4. Scribe the hinge’s offset arm, again using the hinge itself as a template.


5. Adjust the height of a 1/8” router bit to match the thickness of the leaf.


6. Rout about 1/32” shy of the mortise’s layout lines. Clamp two support boards to the door to prevent the router from tipping.


7. Pare to the lines using a wide chisel. Take thin shavings, so you don’t split out the mortise’s thin walls.


8. Temporarily assemble your cabinet, then lay out its hinge mortises. Place shims next to the hinge to determine the gap between the door and cabinet side.


9. If the sides and door of your cabinet are set back, measure this distance. Move the head of the mortising gauge away from the pins by the same amount.


10. Disassemble the cabinet, then scribe mortises on the pieces above and below the door. Remove most of the waste using your router.


11. Clean up the sides of the mortise with a chisel.


12. Place the leaves that have pins in the cabinet mortises. Pre-drill the screw holes using a selfcentering bit. Install the screws by hand.


13. Re-assemble the cabinet and add the other hinge leaves.


14. Slide the door onto the hinges.


15. Install the screws in the door leaves. If everything fits right, glue the cabinet together.


 

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.

 

How to Hang Inset Doors

How to Hang Inset Doors

Install butt hinges perfectly and establish consistent, slender margins.

By Tim Johnson

Purchase the complete version of this woodworking technique story from AWBookstore.com.


Nothing signals skillful craftsmanship like an inset door with elegant hinges and eye-pleasing margins. This challenging job leaves no room for error: Uneven surfaces and unsightly gaps will tell the tale if the hinges, door and frame don’t fit precisely. Like mastering hand-cut dovetails, successfully hanging inset doors on mortised butt hinges is a woodworking milestone. 

I’ll show you a three-step method for installing inset doors that produces great results every time. First, you match the door to the opening. Then you rout mortises for the hinges. And finally, you create uniform, attractive margins between the door and frame. Of course, you can skip the mortising step altogether by choosing different hinges (see “No-Mortise Hinge Options, below”).

To complete the job, you’ll need a couple simple jigs, a mortising bit, and a laminate trimmer. A laminate trimmer is a compact router that’s a really handy addition to any woodworking shop. (If you don’t own a laminate trimmer, this is a great excuse to buy one.) 

Round out your door-installing arsenal with a pair of secret weapons—a plastic laminate sample swiped from the home center and a double-bearing flush-trim router bit. This great new bit should be a fixture in every woodworking shop.


Choose hinges

Your first task is to choose between extruded (also referred to as drawn or cast) or stamped hinges (see photos, above). Extruded hinges are machined and drilled, so there’s virtually no play between the knuckles or around the hinge pin. Stamped hinges are made from thinner stock. Their leaves are bent to form the knuckles that surround the pin. Extruded hinges will last longer, because their knuckles have more bearing surface.

I often use stamped hinges because they cost about one-third as much as extruded hinges and they’re available at most hardware stores. They work fine in most situations. Examine stamped hinges carefully before buying. If you notice large gaps between the knuckles and vertical play between the two hinge leaves, keep looking. Be aware that some stamped hinges are brass plated rather than solid brass. Hinges with loose pins make it easy to remove and reinstall the door, but they aren’t widely available.

Click any image to view a larger version.

6. Rout mortises in the door stile. Locate the mortise at least one hinge length from the top. Because of its small size, a laminate trimmer works great for this delicate job.


8. Rout mortises in the face-frame stiles using the mortising jig. You’ll need a laminate trimmer for this job, because the mortises are so close to the corner. 


10. Rout the door to final length. Use a fence and a flush-trim bit with top- and bottom-mounted bearings to avoid blowing out the back edge. First, rout halfway using the top bearing.


This story originally appeared in American Woodworker May 2006, issue #121.

May 2006, issue #121

Purchase this back issue.

Purchase the complete version of this woodworking technique story from AWBookstore.com.