What's inside
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A triangular-door corner cabinet is a useful first casework project: it fits an unused corner, needs little lumber, and teaches you to build a square box that sits against two walls. The door is the fussy part. Its two angled edges must meet the cabinet opening evenly, so measure the actual cabinet rather than relying on a drawing alone.
Contents
Size and layout
This plan makes a wall cabinet about 24 inches tall, with two 12-inch-deep sides and a 17-inch-wide front. The footprint is a right triangle: the sides meet at 90 degrees in the back, and the front runs diagonally between their ends. A 12-by-12-inch footprint gives a front edge close to 17 inches because the diagonal of a square is about 1.414 times its side.
Before cutting, check the corner with a framing square. Many room corners are not exactly 90 degrees. Hold a cardboard template in place, trim it until it sits flat against both walls, and use it to mark the cabinet’s footprint. Also check for baseboard, pipes, and switches. A cabinet designed to sit tight to the floor may need notches or a wall-mounted cleat instead.
Materials and tools
For a painted cabinet, use 3/4-inch plywood for the sides, top, bottom, and shelf, plus 1/2-inch plywood for the door. A single 2-by-4-foot sheet of each thickness is usually enough for this size, but make a cut list first and allow for saw kerfs. Cabinet-grade plywood is easier to finish cleanly; construction plywood is cheaper but may have voids that show on exposed edges.
You’ll also need wood glue, 1 1/4-inch screws, a triangular or rectangular cleat for mounting, and a small knob. A circular saw guide helps make straight plywood cuts. If you already own a circular saw and can clamp a straight board as a fence, that is fine for a one-off build. A pair of compact cabinet hinges can work, but hinge choice depends on how the door overlaps the front frame; test the layout before drilling.
| Choice | Best for | Trade-off |
|---|---|---|
| 3/4-inch plywood box | A durable cabinet with a simple painted finish | Heavier than a solid-wood frame |
| 1/2-inch plywood box | A very light cabinet with modest loads | Less forgiving at screw joints; needs careful fastening |
| Solid wood door | A stained or furniture-style front | Seasonal movement can alter the fit |
| Plywood door | A stable, painted triangular panel | Exposed plies need edge banding or trim |
Cut the cabinet parts
Cut two side panels 24 inches tall by 12 inches deep. Cut the top and bottom as right triangles, with two 12-inch legs and a front edge about 17 inches long. Cut a shelf to the same triangular footprint, then trim it slightly—about 1/16 inch on each edge—so it can be installed without binding. If you want a face frame, add it after the box is assembled; the frame can cover small plywood gaps.
Mark the top and bottom triangles from a square corner. Confirm the diagonal with a tape measure before cutting. If the two sides are not equal, the front edge and door geometry change, so keep the parts paired and label their inside faces. Sand cut edges to remove splinters, but don’t round over the edges that need to meet flush.
Assemble the box
Lay one side flat, apply glue to the edges of the bottom and top, and fasten them between the sides with screws. Drill pilot holes to reduce splitting; plywood edges are easy to damage, especially near a corner. Use at least two screws at each joint, set back roughly 3/8 inch from the edge. Check that the back corner is square and that the front edges sit in one plane before the glue sets.
Fit the shelf at a useful height, often 10 to 12 inches above the bottom for small items. Support it with cleats screwed to the sides, or use shelf pins if you want adjustability. Cleats are simpler and stronger for a single shelf. A loose shelf that rests only on small pins can sag under heavy dishes, so keep the load modest or add a front support strip.
Fit the triangular door
Measure the finished front opening at the top and bottom. Cut a door panel to the opening size, then trim it down for a consistent gap: aim for about 1/8 inch at the top, bottom, and both angled sides. A door that is too tight will bind when humidity changes or the cabinet is slightly out of square. A gap that is too wide is hard to hide on a plain panel.
Choose the hinge side before drilling. A triangular door can swing from either angled edge, but the door must clear the wall and any neighboring cabinet. Clamp the panel in place with spacers setting the gap, mark hinge positions, and check the swing with a temporary screw or a scrap mock-up. If the hinge instructions call for a round cup hole, use the specified bit and depth; drilling too deep can break through the 1/2-inch panel. For a simpler build, surface-mount hinges avoid cup drilling, though they remain visible.
Install a knob near the free edge, then open the door slowly. If it rubs, identify the high spot and plane or sand only that area. Don’t enlarge every gap to fix one crooked hinge; first check whether the hinge leaf is seated flat and the cabinet is level.
Mount and finish
Fasten a cleat across the back where it can catch wall studs, or attach the cabinet through its sides into studs. Use a stud finder and confirm locations with a small pilot hole. A cabinet holding glass or dishes should not rely on drywall anchors alone. For a small, lightly loaded unit on a masonry wall, choose anchors rated for the wall material and cabinet weight.
Fill screw holes, sand to 180 grit, and seal exposed plywood edges before painting. Edge banding or narrow solid-wood strips conceal plies; filler is cheaper for a painted cabinet but may need two applications. Apply finish to the door’s front and back to reduce uneven moisture absorption. After the finish cures, reinstall the door and adjust the hinges so the reveals stay even.