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Replacing a damaged door jamb, window section, stair component, or other timber part is much easier when the new piece receives an accurate copy of the existing opening. The usual mistake is measuring the opening with a tape and assuming the numbers describe its shape. They do not. An old opening may be out of square, tapered, twisted, or locally damaged. A replacement made from average measurements can fit at the top and fail at the bottom.
The reliable approach is to transfer the opening directly with a template, a pair of gauges, or a combination of marking tools. The best method depends on the size of the part, how much accuracy is needed, and whether the opening is regular enough to measure.
Choose the transfer method
| Method | Best for | Accuracy | Main limitation |
|---|---|---|---|
| Cardboard or hardboard template | Irregular openings, curved profiles, large gaps | High if the template is fitted carefully | Needs room to handle and store |
| Sliding bevel and rule | Angles, splayed sides, and small components | High for straight edges | Does not record a complete shape at once |
| Compass or profile gauge | Short curves, mouldings, and shaped edges | Good for local detail | Can be awkward over long distances |
| Direct scribing | Fitting a replacement against the fixed timber | Very high when done carefully | Requires the new part to be held in position |
For most carpentry repairs, use a straightedge, pencil, combination square, and sliding bevel. Add a cardboard or hardboard template when the opening is large or visibly irregular. A template is not overkill if replacing the part would mean removing it again.
Make a template for an irregular opening
Use stiff cardboard for a one-off indoor repair and 3 mm hardboard for a reusable or larger template. The material should be flat. Corrugated cardboard can compress at the edge and introduce a 1–2 mm error, which is enough to create a visible gap in a door or window repair.
Cut the template slightly oversize. Offer it to the opening and mark where it touches. Trim with a sharp knife, plane, or snips in small amounts. Do not force it into place: a flexible template can buckle and make the opening appear smaller than it is.
Mark the template with “top,” “bottom,” “room side,” and a centreline. Also mark any reference points such as hinge positions, glazing rebates, stops, or the face that must remain flush. Without these labels, it is easy to turn a template over and create a mirrored part.
When the template fits, check it at several points. A useful target is a consistent clearance of about 1–2 mm around a replacement part that will be painted or wedged into position. For a tight, visible join, aim for less than 1 mm, but do not make the fit so tight that seasonal movement or paint prevents assembly.
Transfer angles with a sliding bevel
A sliding bevel records an angle but does not measure it. That is exactly what makes it useful here. Loosen the blade, place the stock against the reference edge, and align the blade with the opening or existing cut. Tighten the screw while holding the bevel firmly against both surfaces.
Transfer the angle to the replacement timber by placing the stock against the corresponding face and drawing along the blade. Keep the bevel orientation marked. If the angle is used upside down, the cut will lean in the wrong direction.
For long or critical parts, take two readings: one at each end. An opening that looks square may be 3–5 mm wider at one end. If the bevels differ, record the difference rather than averaging it. Use a tape measure or rule for the distance between reference points, and a combination square to transfer those distances accurately.
Scribe the replacement part in place
Direct scribing is usually the most accurate method when the replacement can be positioned against the existing timber. Cut the new part deliberately oversize, typically by 2–5 mm on the edge that will be fitted. Support it with wedges or clamps so it cannot move, then set a compass or marking gauge to the widest gap.
Run the compass with one point following the old opening and the pencil point marking the new part. Keep the compass at 90 degrees to the face. If it tilts, the marked line shifts. On a 50 mm-wide board, a modest tilt can change the line by several millimetres.
Do not try to remove the full line in one operation. Saw close to straight sections, then use a bevel-edge chisel set or a block plane to creep up to the line. Leave the pencil line visible until the fit is confirmed. Chisels remove material quickly at corners, so pare with the bevel facing the waste when approaching a shoulder, and use light cuts of 0.5–1 mm.
Use the right marking tools
A sharp pencil is adequate for rough work, but a marking knife gives a cleaner, more repeatable reference. It cuts fibres instead of merely laying graphite on the surface, which reduces breakout when chiselling to the line. A knife line is especially useful across end grain and at hinge or lock recesses.
For repeated offsets, use a marking gauge rather than measuring each point with a tape. Set it once and test the setting on scrap. A quality woodworking marking gauge is worth buying if you regularly fit doors, windows, or trim. For a single basic repair, a pencil, square, and carefully cut cardboard template are cheaper and usually sufficient.
Keep all measurements tied to one datum: the bottom edge, hinge side, or an established centreline. Measuring some features from the left and others from the right allows small errors to accumulate. On a 900 mm part, three separate 1 mm errors can become a 3 mm misalignment by the far end.
Check the fit before final cutting
Dry-fit the replacement with clamps or temporary screws before gluing, painting, or installing hardware. Check the face alignment, reveal, grain direction, and clearances. A door commonly needs a small working gap: around 2–3 mm at the sides and top, with more clearance at the bottom depending on the floor and threshold. Follow the existing construction where it is sound rather than applying a fixed number blindly.
Watch for four common failures: a reversed template, an angle transferred from the wrong face, a bowed replacement board, and a cut made on the waste side of the line. Mark waste with large crosses, label both faces, and inspect the timber with a straightedge before marking. If the part is more than 2–3 mm out of flat over its length, fitting it accurately may be pointless; choose straighter stock or correct the support first.
Spend money on accuracy where the job demands it. A cheap combination square can be fine if its stock is square to the rule; test it by marking a line, flipping the square, and checking whether the two lines coincide. If they do not, use a better square or compensate for the error. For one uncomplicated replacement, careful layout beats an expensive tool. For repeated repairs, a rigid template, sharp marking knife, reliable square, and sharp chisel save both timber and time.