Materials & manufacture · National 5
Measuring & marking out
7 cards · 7 quiz · 0 exam
Design & Manufacture · National 5 · mrkellydt.co.uk
What you're learning in this topic
Learning intention WALT
We are learning about measuring & marking out, specifically to:
understand
- how to mark out a housing, halving or bridle joint
- how to mark out a hole centre, radius and fold line on metal
- why marking out starts from a datum
be able to
- choose the correct marking-out tool for wood, metal and plastic
Success criteria WILF
- I can choose the correct marking-out tool for wood, metal and plastic
- I can describe how to mark out a housing, halving or bridle joint
- I can describe how to mark out a hole centre, radius and fold line on metal
- I can explain why marking out starts from a datum
Why marking out matters N5
- Every accurate part starts with accurate lines. Errors in marking out carry through to cutting, joining and assembly.
- Mark from a datum: the face side and face edge on wood (marked with the face side symbol), or two filed straight, square edges on metal.
- Mark the waste clearly (hatch or cross it) and cut on the waste side of the line.
- Exam tip: in "describe how you would mark out" questions, name the tool and say what it marks. A list of tools scores nothing.
Wood: tools and what they mark N5
| Tool | What it does |
|---|---|
| Steel rule + pencil | Measure and mark positions along the length |
| Try square | Square a line across the face and edges at 90° to the face edge; check squareness |
| Marking knife | Cuts the fibres along a shoulder line so the saw cut is crisp and doesn't tear |
| Marking gauge (one spur) | A line parallel to an edge: depth of a housing, rebate or halving; the centre of a dowel joint |
| Mortise gauge (two spurs) | Two parallel lines at once, set to the chisel width: mortise and tenon, bridle joints |
| Sliding bevel | Lines at an angle other than 90° (dovetails, chamfers) |
| Bradawl | Marks a hole centre and starts screw pilot holes |
Worked example: corner bridle joint N5
- Plane the face side and face edge and mark them.
- Measure the width of the mating piece from the end with a steel rule and mark it with a pencil.
- Square the shoulder line all round both pieces with a try square, then go over it with a marking knife.
- Set the mortise gauge spurs to the width of the chisel (about one third of the timber thickness) and set the stock so the gap is central.
- Working from the face side, gauge the two lines from the shoulder, across the end and back to the shoulder on both pieces without changing the setting.
- Hatch the waste: the middle on the slot piece, the two outer cheeks on the tenon piece.
Cutting: saw down on the waste side with a tenon saw; on the slot, remove the waste with a coping saw then chisel to the shoulder line (or drill out first); on the tenon, saw the cheeks then cut the shoulders with the work held on a bench hook.
Worked example: housing joint N5
- Mark the position of the shelf with a steel rule and pencil, using the shelf itself to set the width.
- Square both lines across the side with a try square and marking knife.
- Set a marking gauge to the depth (about one third of the thickness) and gauge between the lines on both edges.
- Hatch the waste.
Cutting: clamp a guide block on the line with a G-clamp, saw the sides with a tenon saw to the gauge line, remove the waste with a chisel and mallet, and level the bottom with a hand router.
Metal: tools and what they mark N5
| Tool | What it does |
|---|---|
| Engineer's blue (marking blue) | Dye painted on first so scribed lines show up clearly |
| Steel rule | Measure from the datum edge; set odd-leg callipers and dividers |
| Scriber | Scratches a fine, permanent line (the metalwork "pencil") |
| Engineer's square | Lines at 90° to a datum edge, e.g. a fold line; checks squareness |
| Odd-leg callipers | Line parallel to an edge, e.g. a centre line along a bar |
| Centre punch + ball-pein hammer | A dimple at a hole centre so the drill doesn't wander; also the centre for dividers |
| Spring dividers | Scribe circles, arcs and corner radii from a punched centre |
| Template | Draw round for repeated or complex shapes |
Worked example: bracket with a radius, hole and fold line N5
- File two edges straight and square to each other to act as datum edges.
- Apply engineer's blue and let it dry.
- Set odd-leg callipers with a steel rule and run them along a datum edge to scribe the centre lines.
- Centre punch where the lines cross to mark the hole centre.
- For the radius: mark the centre of the arc (odd-legs from both datum edges), centre punch it, set spring dividers to the radius on a rule and scribe the arc.
- For the fold line: measure the position from the end with a steel rule, then scribe across with an engineer's square held against the datum edge and a scriber.
Then: cut the corner with a hacksaw or tin snips, file to the radius line and remove burrs with emery cloth; drill the hole; clamp in bending bars with the fold line level with the top and bend with a mallet.
Plastic (acrylic) N5
- Leave the protective film on and mark on it with a pencil, or use a non-permanent spirit marker or chinagraph pencil on the plastic.
- Use masking tape where the film has been removed; double tape stops a compass point slipping.
- A scriber works but scratches the surface, so only use it on lines that will be cut away.
- Draw round a template for repeated shapes, and mark out in a corner of the sheet to reduce waste.
Key terms
| Datum (wood) | Face side and face edge, planed true and marked, that all measurements are taken from. |
|---|---|
| Datum (metal) | Two edges filed straight and square, used as the reference for all marking out. |
| Engineer's blue | Marking dye applied before scribing so lines show clearly on metal. |
| Marking knife | Cuts wood fibres along a shoulder line for a crisp saw cut. |
| Spring dividers | Scribe circles and radii on metal from a centre-punched point. |
| Fold line on metal | Scribe across with an engineer's square against the datum edge and a scriber. |
| Bridle joint gauge setting | Mortise gauge set to the chisel width, used from the face side on both pieces. |
Quick check
1. Which tool marks both lines of a bridle joint at the same time?
- Marking gauge
- Mortise gauge
- Try square
- Sliding bevel
Show answer
B: Mortise gauge. Two spurs mark both lines in one pass.
2. What is put on mild steel before scribing lines?
- PVA
- Masking tape
- Engineer's blue
- Wax
Show answer
C: Engineer's blue. The blue dye makes scribed lines easy to see.
3. Which tool scribes a corner radius on metal?
- Odd-leg callipers
- Marking knife
- Engineer's square
- Spring dividers
Show answer
D: Spring dividers. Dividers work like compasses from a punched centre.
4. A fold line across a steel strip is marked with…
- Engineer's square and scriber
- Try square and a soft pencil
- Marking gauge and a ruler
- Bradawl and a steel rule
Show answer
A: Engineer's square and scriber. Engineer's square against the datum edge, with a scriber.
5. Why is a marking knife used along a shoulder line?
- To mark a line on metal before filing it
- To cut the fibres for a clean saw cut
- To find the centre of the workpiece
- To mark curved lines accurately
Show answer
B: To cut the fibres for a clean saw cut. It stops the grain tearing at the shoulder.
6. A centre line along a metal bar is best marked with…
- Mortise gauge
- Try square
- Odd-leg callipers
- Sliding bevel
Show answer
C: Odd-leg callipers. Odd-legs run along the edge to scribe a parallel line.
7. Why should marking out start from a datum?
- It is quicker because fewer lines need to be drawn
- It hides any marking-out lines after the part is cut
- It means a try square isn't needed for any lines
- All measurements come from one true reference, so errors don't add up
Show answer
D: All measurements come from one true reference, so errors don't add up. A consistent reference keeps parts accurate.
Printable worksheet
An I do, we do, you do worksheet for this topic, with a separate answer sheet.