Pictorial Sketching
Block out height, width, and depth, then use light construction lines to develop a clear freehand pictorial.
Isometric sketches use three equally spaced directions
Isometric sketches use three equally spaced directions
Draw one axis vertically and the other two down to the left and right, each 30° from horizontal. The three outward rays are 120° apart. Edges parallel to these axes keep those directions throughout the sketch; they can extend either way along each axis line.
Use the same scale along all three axis directions. Lay out width, height, and depth along lines parallel to the axes; an isometric grid helps you keep equal intervals consistent.
Isometric drawing and isometric projection use different scales
An ordinary isometric drawing lays out axis-parallel lengths at the chosen drawing scale. A geometrically projected isometric view foreshortens all three axes equally. Do not mix an isometric projection scale with ordinary drawing lengths in one sketch. The angle of a drawn edge on the paper is not generally its angle on the part.
For CAD view types, see CAD Model Views and Checks.
Locate sloping edges by endpoints; sketch circles as ellipses
Locate sloping edges by endpoints; sketch circles as ellipses
A non-isometric line is not parallel to any of the three isometric axes. Locate both endpoints using width, depth, and height offsets, then join them. Do not lay the true sloping-edge length directly along its apparent direction on the paper.
For a circle on a face parallel to a principal plane, first sketch its enclosing square as an isometric rhombus. Mark the four side midpoints and sketch a smooth ellipse tangent there. Those are contact points, not sharp corners. Keep the curve inside the rhombus.
The circle-to-ellipse rule here applies to circles on the usual top, front, or side planes of the isometric sketch. Do not draw a round circle on one of these tilted faces.
Build a box, locate the cut, then remove material
Build a box, locate the cut, then remove material
Start with the smallest simple box that encloses the part: height, width, depth. In this original example, a corner is removed uniformly through the depth. That makes the front profile a useful starting shape.
- Compare the overall height, width, and depth before adding detail.
- Mark where the cut begins and ends on the front profile.
- Carry those points back along parallel depth lines.
- Connect matching points to form the new face.
- Check the remaining edges, then darken visible edges and lighten or erase construction lines.
“Extrude” means carry a profile through a distance. It is a useful mental model only when the cross-section stays constant over that distance. Check other views for features that stop partway through.
Choose isometric for three directions or oblique for a true front face
Choose isometric for three directions or oblique for a true front face
In an isometric sketch, the three principal directions share one scale, and none of the three principal faces appears in true shape. In an oblique sketch, draw the chosen front face in true shape at the drawing scale, then carry parallel edges back along one receding direction.
A 45° receding direction is common, but it is not required. Full-scale depth is called cavalier; half-scale depth is called cabinet. Keep the chosen depth scale consistent. A circle on the oblique front face stays circular; one on a receding face generally does not.
Both methods use parallel edges rather than perspective vanishing points. Pick the front direction deliberately; see Choosing Drawing Views.
Identify a pictorial Find a non-isometric line Check a circle sketch