Polytechnic · Technical Drawing · Interactive drawing lesson

Datum dimensioning

Every size from one face. Learn datum dimensioning step by step in an interactive Polytechnic technical drawing lesson.

What you will learn

This guided practical demonstrates the construction on a drawing board and explains the method in a clear sequence.

Open the interactive drawing lesson

More Technical Drawing lessons

• Bisecting a line — Find the middle of a line.
• A perpendicular from a given point to a line — Square up from a point on a line.
• A line divided into proportional parts — Split a line into equal parts.
• A perpendicular from any point to a line — Drop a square line onto a line.
• Parallel lines — Draw lines that never meet.
• Bisecting an angle — Cut an angle in half.
• Various angles constructed without a protractor — Build angles with a compass only.
• A copied angle — Copy an angle without measuring.
• The centre of a given arc or circle — Recover a lost centre from two chords.
• Various geometrical shapes — Shapes drawn inside one circle.
• Straight lines joined to curves by an arc — Join a line to a curve smoothly.
• An ellipse and scales — Draw an ellipse and a plain scale.
• First angle orthographic projection — Front view, plan and end view.
• Isometric drawing — Draw a solid on three axes.
• Bars — Round, square and hex bar with breaks.
• Tubes — Show a bore through a broken tube.
• Shafts — Stepped shaft with chamfer and keyway.
• Compression springs — Coils drawn between two envelope lines.
• Tension springs — Closed coils with end loops.
• Splined shafts (external) — Splines on the outside of a shaft.
• Splined shafts (internal) — Splines cut inside a bore.
• Serrated shafts (external) — Fine serrations round a shaft.
• Serrated shafts (internal) — Serrations inside a clamped boss.
• Functional dimensioning — Dimension the sizes that make it work.
• Non-functional dimensioning — Size the rest of the part.
• Auxiliary dimensioning — Reference sizes shown in brackets.
• Chain dimensioning — Sizes taken end to end.
• Datum dimensioning — Every size from one face.
• Types of line — Outline, hidden, centre and break lines.
• Freehand letters and numerals — Print neatly between guide lines.
• Bold lettering for title blocks — Head up a drawing sheet.
• Basic assembly drawings — Parts drawn together and ballooned.
• Exploded diagrams — Pull the parts apart on one axis.
• Orthographic from a pictorial drawing — Turn a 3D view into three views.
• Third angle projection — Plan above, end view on the left.
• Freehand sketches in first angle — Sketch three views without instruments.
• Isometric circles — Four-centre circles on a sloping face.
• Isometric ellipses — Ellipses on all three faces.
• The isometric scale — Shorten true lengths for isometric.
• Sectioned diagrams in first angle — Cut a part and hatch the cut face.
• Hydraulic power steering — Pump, relief valve, control valve and ram.
• Hydraulic power brakes — Pressure supply to the wheel cylinders.
• Hydraulic tipping mechanisms — Raise and lower a tipping body.
• Heavy vehicle air brakes — Compressed air to the brake chambers.
• Basic auto-electrical circuits — Battery, fuse, switch and earth return.