How do I make a picture frame?

Frames are made from mouldings with a rebate along one edge, and everything difficult about them comes from that: four mitres have to close on a shape that is not rectangular in section, on a joint that is half end grain and inherently weak. Getting them right is a matter of sizing from the right thing and cutting in pairs.

What you'll need

• Frame moulding, or timber you can rebate
• A mitre saw, mitre box or shooting board
• A band clamp, corner clamps or strong tape
• Glue and material for corner keys
• Glass or acrylic, backing board and hanging hardware

Step by step

1. Decide the glass size first and work outwards.Standard mount and glass sizes are cheap; odd sizes are not. Pick the glass size, then the mount aperture, then design the frame to fit — rather than the other way round.
2. Size the rebate to swallow everything with room to spare.Glass, mount, artwork and backing board added together, plus a millimetre or two so the backing does not stand proud. A rebate that is too shallow is the most common frame-making error.
3. Allow a few millimetres of rebate width for overlap.The rebate has to cover the edge of the glass and mount without eating into the visible picture. Three to five millimetres of overlap is normal.
4. Calculate the moulding lengths from the rebate, not the outside.The inside of the rebate is what has to equal the glass size plus a whisker of clearance. Add the width of the moulding twice, plus the rebate offset, to get each outside length. Getting this backwards produces a frame the glass will not go in.
5. Cut the mitres in matched pairs.The two long sides must be identical to each other and the two short sides identical to each other. Cut them with a stop block so both come off the same setting; a frame with four correct angles and unequal sides cannot close.
6. Check the mitre angle against a made-up corner, not against the saw scale.Cut two offcuts, hold them together and check with a square. Adjust the saw until that test corner is exactly 90 degrees, then cut the real pieces.
7. Dry assemble the whole frame before glue.All four corners together, held with tape or a band clamp. Check the diagonals and check the glass drops into the rebate.
8. Glue and clamp with even pressure round the frame.A band clamp pulls all four corners at once. The taped method — laying the four pieces in a row face down, taping the outside of each joint, then folding the frame up and taping the last corner — is cheap and works very well.
9. Reinforce the corners once the glue has set.A mitred glue joint is largely end grain and will fail with time. Saw a slot across each corner and glue in a key, or fit V-nails from the back with a proper tool, or drill and glue in dowels.
10. Fit the contents and seal the back.Glass, mount, artwork, backing board, then flexible points or turn buttons to hold it in, then gummed tape round the back edge to keep dust out.
11. Fit hanging hardware sized for the weight.D-rings and cord about a third of the way down from the top, or a proper hanger for a heavy frame. Check the wall fixing is rated for the load.

Tips

• Acrylic glazing instead of glass is worth considering for large frames, anywhere children are, and for anything being posted — it is far lighter and does not break dangerously, though it scratches more easily.
• Cut the moulding slightly long on the first cut of each piece and creep up on the final length. A frame member cut short cannot be recovered.
• If a corner has a hairline gap, close it by burnishing the wood over with the back of a chisel before finishing rather than filling it.

Common mistakes

• Sizing the frame from the picture instead of the glass — The picture is usually mounted, and the glass and mount sizes are what actually sit in the rebate. Framing to the artwork size produces a frame that nothing standard fits.
• Cutting the rebate too shallow — The backing board then stands proud of the frame and cannot be held in. There is no fix short of deepening the rebate on an assembled frame, which is very awkward.
• Relying on glue alone at the mitres — The joint is half end grain. It will hold for a while and then open, particularly on a large frame carrying glass.

Questions people ask