Use an imaginary cut to expose the interior

A section view shows what is inside a part without making you untangle a group of hidden lines. Imagine cutting the part, removing the material between you and the cutting plane, and looking at what remains.

The cut changes the drawing representation, not the manufactured part. Hatch the material crossed by the plane and show the useful visible edges beyond it. Hidden lines are usually omitted in sections unless needed to make the shape clear.

Start with The Alphabet of Lines and Orthographic Projection and the Glass Box if the line types or viewing directions are unfamiliar. For a sloping face or a small feature, see Auxiliary and Detail Views.

Full sections cut all the way through the part

A full section uses one plane through the entire part. For this hollow cylinder, a plane through the axis exposes both walls and the bore. The bore is empty space and receives no hatching.

Half sections combine the exterior and interior

A half section is useful for a symmetric part. Imagine removing one quarter with two perpendicular cutting planes. The resulting view shows one half in section and the other half as an exterior view, usually divided by a center line.

It is not a full section with half its hatch erased. The unsectioned half shows the outside, and symmetry supplies the connection between the two halves.

Offset sections reach features that are not in one straight line

An offset section jogs the cutting plane to pass through several features. Project the selected parallel portions into one section. The jogs help explain the cut location; they do not create physical edges on the part.

Read the parent view for the holes’ actual locations. Their appearance together in the section does not mean they lie in one straight row.

Broken-out sections expose only a local area

A broken-out section removes a limited patch to a chosen depth in an existing view. An irregular break line marks the boundary. Use it to expose a small passage or wall without adding a complete section view.

A separate cutting-plane line is normally unnecessary: the local boundary identifies the area. Depth still matters; a cut that stops before a bore will not reveal it. This differs from a broken view, which merely shortens a long part on the sheet.

Revolved sections show a cross section in place

A revolved section turns a cross-sectional slice 90° into the plane of the drawing and places it on the parent view. It is useful for the shape of a bar, spoke, or arm. Show the slice itself, rather than the features behind the cut.

Removed sections place the slice clear of the parent view

A removed section places the cross section away from the parent view to keep it readable. Match its identifying letters to the cutting plane. Several removed sections can describe changes along a long part; keep each location unambiguous.

Aligned sections rotate an angled portion into the section plane

An aligned section uses intersecting cutting planes through features arranged around an axis. An angled portion is rotated into alignment before it is shown in the section. This makes radial features easier to read.

Do not infer angular spacing from the aligned result. In this disk, one small hole is rotated into the section plane; its original angular position is established by the top view.

Hatch cut material, with conventional exceptions

Use thin, evenly spaced diagonal lines, commonly near 45° to the main outline. Change the angle when the hatch would be confused with an edge. Keep a part’s hatch consistent; distinguish adjacent assembly parts by changing hatch angle or spacing.

• Voids: holes and open spaces are never hatched as solid material.
• Ribs, webs, and spokes: a cut along their length generally leaves them unhatched so they do not look like a thick solid wall. A transverse cut through their thickness is hatched.
• Shafts and fasteners in assembly sections: when cut lengthwise through their axes, solid shafts, bolts, nuts, washers, pins, and similar standard parts are commonly shown unsectioned. A transverse shaft section can be hatched; “never hatch a shaft” is too broad.

An unhatched region may be empty space, an uncut surface, or a conventionally unsectioned component. Use its outline and the other views to decide which.

Supporting detail: Addendum 2 — Drawing standards and scope.

Extra views make sloping surfaces and small features easier to read

An auxiliary view is an extra drawing view that looks straight at a flat, sloping surface so its shape is clear. A tilted rectangular surface can look shortened from above; looking straight at it reveals its rectangular proportions.

A detail view is an enlarged picture of a selected small region, such as a hole with crowded edges or dimensions. The actual part stays the same size. Use an auxiliary when the viewing direction makes the shape hard to read, and a detail when a small region needs more room.

A view's scale tells you how large its picture is compared with the real part. Read the view labels and scale information to connect an added view to the original drawing. To expose an interior hidden behind solid material, use a section view.

Look perpendicular to a face to see its true shape

A face is a surface on the part. Look straight at a flat face, perpendicular to it, to see its true shape. In projection terms, that face is parallel to the imaginary flat surface on which the view is drawn: the projection plane.

In the figure, the part is a wedge with a flat, sloping rectangular face. The front view sees that face edge-on, so the face is reduced to the line P–Q. The light-blue rectangle is the same face viewed straight on in the auxiliary view.

In this example, the front view sees the inclined face on edge. The top view shows it foreshortened: its sloping length appears shorter because the view is not looking straight at the face. The top view's 160-unit length is not the face's true 200-unit length.

Scale is the ratio of a length on the drawing to its actual length. “True shape” still allows the stated drawing scale; it does not mean the image must be life size. The auxiliary view shows the face's correct proportions without the shortening caused by the viewing direction.

A primary auxiliary view is constructed directly from a principal view, such as the front, top, or side. Choose its projection plane parallel to the inclined face. Review Orthographic Projection and the Glass Box and Choosing Drawing Views for the principal views.

Supporting detail: Addendum 4 — When one auxiliary view is not enough.

A detail enlarges a feature; a break shortens the view

The existing view from which a detail is taken is its parent view. A boundary and letter usually identify the selected region. In the figure, the circle marked B locates the region shown in Detail B.

Match the detail label and read its scale. 2:1 means a drawn length is twice the actual length; the hole itself has not grown. Enlargement alone does not change the viewing direction or reveal hidden features.

A broken view omits a middle length of a long, substantially uniform part so its ends and features fit on the sheet. Break lines identify the omission. The actual part remains continuous, and dimensions across the break state its full size. Use those dimensions rather than measuring the shortened illustration.

A broken view is different from a broken-out section, which shows interior geometry by representing a local portion of material as removed. See Section Views.

Project from the edge view and transfer the missing depth

The auxiliary figure above uses the front view as its parent. Its thin projectors are construction lines used to line up corresponding points in the two views.

1. Find the principal view in which the face is a line. In the example, the front view shows the sloping face edge P–Q.
2. Draw a fold or reference line parallel to P–Q. It represents the hinge between the parent and auxiliary projection planes.
3. Draw thin projectors perpendicular to the fold line from the face’s corners.
4. Transfer each corner’s depth from the corresponding principal view, using the same reference and drawing scale. Here the top view supplies a constant depth of 80.
5. Connect corresponding points. The face is a 200-by-80 rectangle in the auxiliary view, although the top view shows its sloping length shortened to 160.

These are invented drawing units for the construction. The projectors and fold line are not physical edges on the part. The auxiliary view shows this face's true shape, not necessarily the true shape of every other face.

Use a partial auxiliary view when only one face matters

A partial auxiliary view shows the useful inclined face and enough nearby geometry to identify it. Omit unrelated geometry that would make the view crowded, using an appropriate break boundary where the view is interrupted.

Keep the viewing reference, label, and scale clear. Partial means limited coverage; it does not change the projection direction. The construction above isolates the inclined face for that reason.

Create auxiliary, detail, and break views from the parent in CAD

Auxiliary view

Select the parent and a reference edge representing the inclined face edge-on. Use Auxiliary View in SOLIDWORKS or Auxiliary view in Onshape, check the direction, and place the view. For a partial view, limit the displayed region with the application’s crop or partial-view controls while retaining identifying references.

Detail view

Use Detail View in SOLIDWORKS or Detail view in Onshape. Define the region, place the enlarged view, and set its scale and label. Verify that dimensions reference the intended model edges.

Broken view

Use Break View in SOLIDWORKS or Break view in Onshape. Choose break direction and style, then position the two break boundaries. Check that no feature needed to define the part was omitted.

Review the result after every model revision. A generated view can be geometrically valid yet omit the feature the reader needs.

Supporting detail: Addendum 5 — Vendor help and dimensioning references.

Practice choosing the true-shape view Practice reading a broken view