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Knife Hinges for Cabinets

What are Knife Hinges?

Knife hinges are the flat-styled cabinet hinges.  Typically, knife hinges go in areas where semi-concealment is necessary because their flat and compact design makes them suitable for the part.

The primary purpose of a knife hinge is to open fully and allow a door to lie totally flat against its neighboring cabinet, while concealing as much of the metal as possible. During installation, one has to mortise these hinges into the cabinet door’s top or bottom edge and also at the top of its frame.

All that the cabinet does show of the hinge is its pin that serves as the axis point of the pivoting movement. Shape wise, you will find a knife hinge closely resembling a pair of scissors, with its two parts (what we call leaves) connecting to its pivoting point.

What are Knife Hinges used for?

Knife hinges are neat and simple.  You can find two kinds of knife hinges, including straight and offset.

One uses the straight knife hinge when the bottom and top part of the cabinet’s door project past the two gables. When the door has to overlay the gables, the straight knife hinge works perfectly well for the cabinet.

On the other hand, an offset knife hinge is useful in a situation where the gabbles, bottom and top of the cabinet are in line and the door is to be inset. Knife hinges are different from the traditional hinges. The main difference lies in how the leaves for the former mortise into the ends and top of a cabinet and the bottom of its frame too.

When you install a knife hinge, the pivot point is really all that one can see. While most of these hinges enable a door to open completely and rest against their neighboring cabinet, some knife hinges now come with built-in stops too to restrict how much the door will open.

How to Install Knife Hinges

Here is a step by step guide to help you through this task:

  1. Begin the process by ensuring you assemble the face of your dry carcase square and flat. Before you glue up the carcase, follow these steps in order:
    1. Lay both of your carcase hinge mortises flat out
    2. Next, you have to dissemble your carcase
    3. Take the hinge mortises and then rout and pare them next
    4. You can then glue the carcase and wait till it dries out completely
    5. Verify your carcase lies square across its opening
    6. Flatten the face of your carcase next, by sanding or plane technique
  1. If you want your door to have a consistent reveal, make sure the shims are identical in thickness as the hinge washer. You can choose between cardboard or plastic laminate and other materials.
  2. In the next step, you must lay out your hinge mortises with the help of a pencil. Place a laminate shim between the hinge and your carcase wall. Then mark the edge of the hinge’s short leg in the shape of ‘L’ and the hinge leaf. With these reference lines, you will have a limit for marking the gauge in your next step.
  3. You must now mark the gauge line to establish the mortise’s front edge. Then following the pencil mark to pencil mark, start scratching a gauge-mark line. You have to set the marking from the center point of your pivot pin to outside edge of the long leg of your hinge leaf. At this point, you must try your best to protect the gauge from wandering off a sloping grain.
  4. Take hold of your knife now and place your hinge leaf in location on the marking-gauge line. Then with you knife, mark the inside edge of your ‘L’ and also the end of your hinge leaf. After completing this step, you are free to erase the pencil lines.
  5. You can continue mortising your carcase by penciling in the back edge of it. This line will keep you safely within limits when you rout the hinge mortise.
  6. You now need to use a 3/16-in bit set for hinge leaf’s thickness. Try to keep far away from the knife marks and pencil mark defining your mortise.
  7. Do not let your mortise extend farther than the knife mark
  8. Using a chisel, remove all the waste left behind the mortise.
  9. Fit your door snugly into the carcase opening. If need be, trim it so that the door fits precisely in the opening.
  10. Place your hinge leaves into the corresponding mortises.
  11. Screw the bottom of your door hinge leaf and the carcase hinge leaves into place.
  12. Proceed with the final fitting of the door.

Types of Knife Hinges

You will find two types of knife hinges, including:

  1. Straight knife hinge
  2. Offset knife hinge

Straight Knife Hinge

Straight knife hinges are appropriate for doors overlaying a frame. If a door is inset into the bottom and top or is overlaying the sides, then straight knife hinges work best for it. As for mortising, it is not overly complicated and one shouldn’t have a problem as long as they cut it by hand or cut the ones in the casework before assembling them.

Offset Knife Hinges

The offset knife hinge has a particular shape, as its name suggests. His hinge type is particularly ideal for inset doors because of its function of moving the pivoting point away from the frame. If we compare it against a straight knife hinge, we’d find offset hinges trickier to install.

However, the key to success lies in not only cutting the mortises accurately but also locating them precisely. Use a routine jig if need be but once you have managed this bit well, the rest becomes easy. 

Final Thoughts

A knife hinge plays a vital role in cabinet-making and takes much of the responsibility for its high-quality and smooth-functioning. If you install a knife hinge on your own, you must be extremely patient, steady and skillful to handle the task as even a slight misalignment can ruin the performance quality.

Rest assured, if you’re looking for hinges that virtually disappear in your cabinetry and lend an over neat, sleek and polished look, then knife hinges are the best option for you.

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