Plate with a rectangular window

A plate with a rectangular window cut straight through it, from front face to back face. Draw the front, top and right-side views. The window is not round, so it carries no centre lines — but it does have edges that cannot be seen from every direction, and an edge you cannot see is drawn dashed rather than left out.

First angle projection

The part

Dimensions in mm

Line

Orthographic projection: hints

Hidden edges are dashed, not solid
An edge you cannot see from that view — because material in front of it blocks the line of sight — is still drawn, but as a dashed line, never a solid one. Leaving it out is as wrong as drawing it solid: both claim something about the part that isn't true.
Every circular feature gets centre lines
A hole or a boss is marked with a thin centre line through its axis in every view — a cross in the view that shows it as a circle, and a long-short-long line along its length in the views that show it edge-on. This is true whether the circle is visible or hidden.
First-angle and third-angle place views differently
The same three views go in different positions depending on the convention: in first-angle the top view sits below the front view; in third-angle it sits above it. Check which convention the drill states before you start placing views, not after.
The three views must line up with each other
Front and top share the same width and stay aligned on the same vertical lines; front and side share the same height and stay aligned on the same horizontal lines. If a feature drifts sideways between the front and top view, one of them is wrong.
A view shows an outline, not a surface
Draw the silhouette and every edge where two faces meet at an angle — not a flat face just because it faces the viewer. A flat face with nothing crossing it contributes no interior lines at all, even though it fills most of the view.
Count the edges before you commit to the drawing
Before drawing a view, count how many distinct edges the part should show from that direction — including hidden ones. A step or a notch adds edges in some views and none in others; if your count doesn't match what the isometric implies, look again before you draw.

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