This convention may take some experience. It is helpful to choose the placement of the dimension in the order in which a machinist would create the part. This gives the dimensions a reference standard. It is often better to measure from one end to various points. Repeatedly measuring from one point to another will lead to inaccuracies.
Not only will these clutter the drawing, but if "tolerances" or accuracy levels have been included, the redundant dimensions often lead to conflicts when the tolerance allowances can be added in different ways. Put in exactly as many dimensions as are necessary for the craftsperson to make it -no more, no less. As a general guideline to dimensioning, try to think that you would make an object and dimension it in the most useful way. We have "dimensioned" the object in the isometric drawing in figure 7. The circular object in figure 6 requires only two views.įigure 6 - An object needing only two orthogonal views.įigure 7 - An isometric view with dimensions. For example, some objects need only two views, while others need four. Three views are not always necessary we need only as many views as are required to describe the object fully. Which views should one choose for a multiview drawing? The views that reveal every detail about the object. We call this an "orthographic" or "multiview" drawing.įigure 4 - The creation of an orthographic multiview drawing.įigure 5 - A multiview drawing and its explanation. Unfold the box (figure 4) and you have the three views. Then draw the object on each of three faces as seen from that direction. Imagine that you have an object suspended by transparent threads inside a glass box, as in figure 3.įigure 3 - The block suspended in a glass box. In order to get a more complete view of the object, an orthographic projection may be used. However, if the object in figure 2 had a hole on the back side, it would not be visible using a single isometric drawing.
One can pack a great deal of information into an isometric drawing. If the isometric drawing can show all details and all dimensions on one drawing, it is ideal. Lines that are not parallel to these axes will not be of their true length.Īny engineering drawing should show everything: a complete understanding of the object should be possible from the drawing. When drawn under these guidelines, the lines parallel to these three axes are at their true (scale) lengths. In an isometric drawing, the object's vertical lines are drawn vertically, and the horizontal lines in the width and depth planes are shown at 30 degrees to the horizontal. This is one of a family of three-dimensional views called pictorial drawings. The representation of the object in figure 2 is called an isometric drawing. Before we get started on any technical drawings, let's get a good look at this strange block from several angles.įigure 1 - A Machined Block. We hope you like the object in Figure 1, because you'll be seeing a lot of it. Don't worry about understanding every detail right now - just get a general feel for the language of graphics. "Drawing" usually means using drawing instruments, from compasses to computers to bring precision to the drawings. "Sketching" generally means freehand drawing. We will treat "sketching" and "drawing" as one. The purpose of this guide is to give you the basics of engineering sketching and drawing. This is especially true for the engineer. One of the best ways to communicate one's ideas is through some form of picture or drawing. Sections of Objects with Holes, Ribs, etc. To see an animated version of this tutorial, please see the Drawing and Drafting section in MIT's Engineering Design Instructional Computer System.