How to make a picture frame

A picture frame is four mitred lengths of wood with a groove in the back. Everything difficult about making one comes down to two things: cutting four 45-degree angles that actually add up to 360, and gluing end grain to end grain in a way that holds.

What you need

Essential:

• A mitre saw, or a mitre box and a fine-toothed backsaw
• A table saw or a router with a rabbeting bit
• A band clamp or strap clamp, or four corner clamps
• PVA wood glue
• A reliable square
• Sandpaper, 150 through 220 grit

Very helpful:

• A stop block for repeatable cuts
• A shooting board and a sharp block plane, for truing mitre faces
• A slot-cutting jig for splines

Materials: enough moulding for 2(width + height) + 8 × face width, plus 10% waste. See the moulding guide for how to buy it and wood selection for what to buy.

Step 1: cut the rabbet first

Cut the rabbet along the entire length of your stock before cutting anything to length. Running a full-length piece through a saw or router is safer, more accurate, and gives a continuous groove with no chance of misalignment between rails.

On a table saw, two passes: one with the stock flat and the fence set to the rabbet width, one with the stock on edge and the fence set to the rabbet depth. The waste falls away on the second cut — make sure it falls to the outside of the blade, not trapped between blade and fence.

On a router table, a rabbeting bit with the right bearing does it in a single pass, though a deep rabbet is better taken in two or three shallow passes than one heavy one.

Size the rabbet for what will go inside: a quarter inch for glazing, print and backing; three eighths for a single mat; half an inch for a double mat or thicker glazing.

Step 2: get the mitre angle genuinely right

Do not trust the 45-degree detent on a mitre saw. Most are close and few are exact, and a half-degree error at each of four corners becomes a two-degree gap by the time the frame closes.

The test: cut two scrap pieces at your saw's 45 setting, put them together, and check the resulting corner against a reliable square. If there is light at the outside, the angle is under 45; light at the inside means it is over. Adjust and re-test until the corner closes against the square with no light at all.

Do this once, then do not touch the saw setting until all four pieces are cut.

Step 3: cut to length, in pairs

The two horizontal rails must be identical to each other, and the two verticals must be identical to each other. Identical, not approximately.

The reliable method is a stop block: clamp a block to the saw fence at the correct distance, butt each piece against it, cut. Two cuts against the same stop are the same length by construction, which is a far better guarantee than two measurements.

The length you need is the inside (rabbet) length, which equals the artwork size plus about an eighth of an inch of clearance. Measure and mark on the rabbet edge, not the face, because the face is longer by the moulding width at each end.

Cut the four pieces, then dry-assemble them and hold them together with the band clamp. Look at all four corners. If one is open, one rail is short — find it now rather than after gluing.

Step 4: glue the joints properly

End grain drinks glue. A mitre joint is end grain against end grain, which is why a frame glued the way you would glue a face joint will come apart.

The technique that works:

1. Brush a thin coat of glue diluted about one part water to four parts glue onto each mitre face. This is sizing — it fills the open end grain rather than being absorbed away from the joint.
2. Wait five to ten minutes until it is tacky but not dry.
3. Apply full-strength glue to both faces.
4. Assemble and clamp.

A band clamp pulls all four corners simultaneously and self-squares if the pieces are cut accurately. Tighten in stages, checking the diagonals: measure corner to corner both ways, and when the two diagonals are equal, the frame is square. Adjust by nudging the long diagonal before the glue sets.

Leave it clamped for at least an hour, and do not stress the joints for 24.

Step 5: reinforce the corners

Glue alone on end grain is not enough for anything you want to last. Three options, best first.

Splines. Cut a slot across each corner, on the outside face, running diagonally through the joint. Glue a thin strip of wood into the slot and trim it flush when dry. This puts long grain across the joint and is dramatically stronger than glue alone. In a contrasting timber it also becomes a visible detail that says the frame was made rather than bought.

V-nails. Wedge-shaped fasteners driven into the back of the joint. This is the professional method and needs an underpinner, which is a real machine. Some can be driven by hand with a special tool for light frames.

Corrugated fasteners. Hammered across the joint at the back. Fast, effective, and visibly crude. Fine for a shop frame, wrong for anything else.

Step 6: sand and finish

Sand progressively — 150, then 180, then 220 — always with the grain, and pay attention to the corners, where a mitre almost never meets perfectly flush. Sand the corners as a single surface rather than each rail separately.

For painted frames, finish after assembly: fill any hairline corner gaps with a fine filler, prime, sand lightly, then two thin coats of paint. Thin coats sprayed or brushed out well beat one thick coat every time.

For oiled hardwood, finish before assembly is often easier, because getting an even oil finish into a tight inside corner is awkward. Mask the mitre faces so glue still has bare wood to bond to.

For stained work, apply a wood conditioner first on anything blotch-prone — maple, pine, birch — and test the stain on an offcut from the same board. Stain on a test piece from a different board tells you nothing useful.

Step 7: fit the hardware

Cut the glazing and backing about a sixteenth of an inch under the rabbet size so they drop in without forcing.

Hold everything in with flexible points driven into the rabbet wall with a point driver, or with small brads tapped in carefully. Then seal the back with gummed paper tape across the join between backing and frame — it keeps dust and insects out and makes the back look finished.

For hanging, fit D-rings about a third of the way down from the top on each side and run picture wire between them with a few inches of slack. Sawtooth hangers are quicker and cannot be levelled. At anything above 16x20, use two wall hooks rather than one; the hanging guide covers fixings by weight.

The mistakes that cost the most time

Cutting to the face length instead of the rabbet length. The frame comes out too big by twice the moulding width, and there is no fix.

Measuring each rail individually. Two rails measured separately are never quite the same. Use a stop block.

Skipping the glue sizing. The joint feels fine when clamped and opens within a year.

Finishing before filling. Corner gaps filled after finishing show as a different colour forever.

Clamping a frame that was never square. A band clamp will happily hold a parallelogram. Check the diagonals every time.