A Complete Guide to Industrial Drafting

An engineering drawing is not a picture; it is a set of build instructions. The test of a good one is not how it looks: a good drawing is one that two different people read the same way.

This guide follows the order the work actually happens in.

1. Choosing views — as few as possible

The rule: the smallest number of views that fully defines the part.

Three views is a habit, not a law. Many parts are complete with two views, or one view plus a few callouts:

Rotational parts (shafts, bushings): one longitudinal view plus diameters. The second view adds nothing.
Flat sheet parts: one view plus thickness as a t note.
Prismatic parts: usually two or three views are needed.

Choose the principal view to carry the most information with the fewest hidden lines. Usually that is how the part sits in the machine that makes it.

2. Section views — when and how

Whenever internal detail matters, use a section instead of hidden lines. Hidden lines create ambiguity; sections do not.

Hatching rules that are routinely broken:

Hatch only cut material — never empty space or bores
45°, evenly spaced
Within one part, all hatching runs the same way at the same spacing
In an assembly, each part gets a different angle or spacing
Bolts, nuts, solid shafts and keys are not hatched in longitudinal section

3. Dimensioning — where to measure from

This is the most decisive part of the drawing.

Datum dimensioning references every dimension to one face. Errors do not accumulate.

Chain dimensioning references each dimension to the previous one. Every stage's error rides on the next and piles up at the end of the chain.

Five chained dimensions at ±0.1 each can total ±0.5. Dimension from a datum almost every time.

Choose the datum to be the face the part is clamped on or the face that references it in the assembly. If the drawing's datum differs from the machining datum, the maker has to convert — and that is where error enters.

Basic rules

Each dimension appears once only
Put dimensions outside the part, not across it
Dimension lines should not cross part lines
Small dimensions nearest the view, larger ones further out
Diameter with Ø, radius with R, square with □

4. Tolerances — only where they earn their place

A tight tolerance on a surface that does no work is just money. A simple test:

If this face does not mate, rotate, seal or bolt to anything — a general tolerance is enough.

For everything else, put ISO 2768-m in the title block and be done. You do not need a number on every dimension.

Reserve specific tolerances for:

Bearing and bushing seats
Press-fit surfaces
Centre-to-centre distances on bolt patterns
Sealing dimensions
Dimensions that stack up in an assembly

5. Surface finish

Ra states surface roughness. Common values:

Ra	Produced by	Typical use
12.5	Rough turning, cutting	Free surfaces
3.2	Ordinary turning	General surfaces
1.6	Finish turning	Mating surfaces
0.8	Reaming, fine finishing	Bearing seats
0.4 and below	Grinding	Sealing faces, rotating shafts

Each step down raises cost noticeably. If you do not specify, the maker chooses the cheapest — which is usually right.

6. The title block

At minimum it should carry:

Part name and drawing number
Material — with a specific grade
Surface treatment — plating, paint, hardening
Scale
Units (normally millimetres)
General tolerance (ISO 2768-m)
Designer name and date
Revision number — without it the shop cannot tell whether their copy is current

7. What gets forgotten

Edge chamfers. Write 1×45° chamfer on all sharp edges or the edge stays sharp.
Internal corner radii. If unspecified, the maker uses whatever tool is at hand.
Keyway orientation relative to a reference face.
Thread class — M10 is not enough; M10×1.5-6H is complete.
Quantity on repeated holes: 4× Ø8.

8. A final checklist

Before sending a drawing out:

[ ] Could this part be made from this drawing without a single phone call?
[ ] Does each dimension appear only once?
[ ] Is the datum identified?
[ ] Are material and surface treatment stated?
[ ] Are all threads fully specified?
[ ] Chamfers and corner radii?
[ ] Is the revision number current?
[ ] Is the drawing legible at print size?

Take the last one seriously: a drawing that reads well on a monitor may be unreadable printed on A4. The shop prints it.

If you have a drawing and want it checked before it goes to a workshop, send it over. There is usually one or two things worth catching before they become rework.