Advanced Project: Make a Display Case with Mitred Corners and Splines

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A small display case is an unforgiving project: mitres that look close on the saw can open into visible gaps at assembly, and a weak corner can split when you fit the glass. This build uses a hardwood frame with splined mitres, a plywood back and a removable front panel. The splines reinforce the joints and add a contrasting detail if you choose a different wood.

Dimensions and design

The example case measures 18 inches wide, 14 inches high and 5 inches deep. Adjust the dimensions to suit what you plan to display, but keep the frame members wide enough to leave room for a groove and spline. Use straight-grained stock about 3/4 inch thick and at least 2 inches wide; you can rip it to final width after milling.

This design has four mitred rails and stiles forming a rectangular frame. A groove along the inside edges holds a 1/4-inch plywood back and a clear front panel. The front panel is captured in a shallow rabbet, with small retaining clips on the back so it can be removed for cleaning or changing the display. Measure the actual glass or acrylic before cutting the frame openings.

Tools and materials

You’ll need a table saw or mitre saw, a spline-cutting jig, a sharp blade, clamps, a square, a router or table-saw setup for the grooves, and a drill for the mounting hardware. A dedicated table-saw spline jig can make the cuts repeatable, though a well-built shop-made jig works too. For accurate mitres, a precision mitre gauge is useful but not essential if your saw and fence are already set up accurately.

Choose hardwood that machines cleanly, such as cherry, walnut, maple or oak. Use 1/4-inch plywood for the back, clear glass or acrylic for the front, wood glue, and finish. Glass resists scratches better; acrylic is lighter and less likely to break, but scratches more easily. For a case that will hang, use a French cleat or two screws into wall studs rather than relying on picture wire.

Cut and prepare the frame

Mill the stock flat and square before cutting the mitres. Rip four frame pieces to 2 inches wide. Cut two long pieces and two short pieces with matching 45-degree ends; make the long and short dimensions refer to the outside points of the mitres. Cut the parts slightly long at first, then sneak up on final length after checking the first pair.

Test the saw setting on scrap. Bring two mitred offcuts together against a square; the joint should close along its full length without pressure. A small error compounds across four corners. If the saw is out by even a fraction of a degree, the assembled frame may bow or show gaps. Use a stop block to cut matching pairs, and label each piece so the grain and orientation stay consistent.

Cut a 1/4-inch-wide groove about 3/8 inch deep along the inside edge of each frame piece for the back panel. Make the groove before assembly, stopping it short of the mitre ends if you don’t want it visible from outside. Cut a shallow rabbet on the front inside edge to hold the glazing. Leave about 1/8 inch of clearance around the panel so seasonal movement or slight measurement differences don’t bind it.

Glue and clamp the mitres

Dry-fit the four pieces on a flat surface and check both diagonals. If the diagonals differ, the frame is out of square. Adjust the joints before applying glue; clamps can close small gaps, but they won’t fix inaccurate cuts without twisting the case. Apply a thin, even coat of glue to each mitred face. Use a band clamp or four corner clamps, then recheck the diagonals and square while the glue is still wet.

Wipe away squeeze-out with a damp cloth, taking care not to push glue into the grooves. Let the frame cure according to the glue label, typically overnight before machining or loading the joints. A common failure is using too much clamp pressure: it can bow the frame or force glue-starved joints apart when released.

Cut and fit the splines

Set the frame in a spline jig and cut a centered kerf across each outside corner. A kerf around 1/8 inch wide and 3/8 inch deep is a useful starting point for a 3/4-inch-thick frame. Make a test cut in scrap first and keep fingers clear of the blade. If you don’t have a table saw, a router and a stable corner jig can work, but take shallow passes and verify the slot stays centered.

Cut spline stock from straight-grained hardwood so its grain runs across the joint, not parallel to the kerf. Make it slightly thicker than the slot, then plane or sand it until it fits snugly by hand. A loose spline adds little strength; one that needs hammering can split the mitre. Glue the spline, press it into the slot, and trim it flush after curing. A contrasting species makes the spline decorative; matching wood keeps the corner quieter.

Fit the panels and finish

Measure the assembled grooves and rabbet, then cut the plywood back and front panel to fit with a little clearance. For a 1/4-inch groove, the back panel should slide in without force. Sand the frame through 180 or 220 grit, ease sharp edges, and apply finish before installing the glazing. Keep finish out of the grooves and rabbet, where thick buildup can prevent a proper fit.

Set the front panel into the rabbet and hold it with small turn buttons or glazing clips screwed into the frame. Don’t glue the glass or acrylic in place. If using acrylic, remove its protective film only after machining and handle it with clean gloves to reduce scratches. Attach the back with screws or small turn buttons so it can be removed later.

Choosing a joint and cutting method

For a display case that will be moved or hung, splined mitres are a practical upgrade. If the case is small and stays on a shelf, a plain glued mitre may be adequate; spend the saved time on accurate cuts and careful panel fitting instead.

Mount and check the case

Before loading the case, check that the back sits flat, the glazing is secure and all four corners remain closed. Mark the hanging position through a French cleat or mounting holes, and fasten into studs where possible. A loaded case can be much heavier than it looks, especially with glass and metal objects inside. Start with a light load, then check for movement or sag before adding valuable pieces.