12 Dec SECTIONING IN ENGG DRAWING. 1. SECTIONING; 2. Sections are used to show interior details clearly. A cutting-plane line shows. Orthographic Views & Sectioning. Prof Ahmed Kovacevic. Engineering Drawing and Design – Lecture 4. School of Engineering and Mathematical Sciences. 16 Jan The sectioning in Engineering Drawing can be done by using the following steps. 1) First, decide about the correct positioning of the cutting.
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We cannot tell what the inside of the part looks like from this view.
We have to make some choices when we dimension a block with a notch or cutout figure In some cases this method can be clearer than just dimensioning between surfaces. One of the best ways to communicate one’s ideas is through some form of picture or drawing. When drawn under these guidelines, the lines parallel to these three axes are at their true scale lengths. This gives the dimensions a reference standard. A half-section is a view of an object showing one-half of the view in section, as in figure 19 and This convention may take some experience.
It corresponds closely to what you actually see when viewing the object from a particular angle. More usually, the type of material is indicated elsewhere on the drawing, making the use of different types of cross-hatching unnecessary.
Usually hidden dotted lines are not used on the cross-section unless they are needed for dimensioning purposes. If the drawing is made without either instruments or CAD, it is called a freehand sketch. As a general guideline to dimensioning, try to think that you would make an object and dimension it in the most useful way.
Isometric drawings can show overall arrangement clearly, but not the details and the dimensions.
In order to get a more complete view of the object, an orthographic projection may be used. Then, for clarity, we add the overall length of 60 and we note that it is a reference REF dimension.
Also, some hidden lines on the non-sectioned part of the drawings are not needed figure 12 since they become redundant information and may clutter the drawing. The circular object in figure 6 requires only two views. The spacing between lines should be uniform. These lines are called section lining or cross-hatching. A leader may also be used to indicate a note or comment about a specific area. Unfold the box figure 4 and you have the three views.
In figure 29 we have shown a hole that we have chosen to dimension on the left side engineeering the object.
The dimension line is a thin line, broken in the middle to allow the placement of the dimension value, with arrowheads at each end figure It is helpful to choose the placement of the dimension in the order in which a machinist would create the part.
This eliminates the addition of measurement or machining inaccuracies that would come from “chain” or “series” dimensioning. We can get around this by pretending to cut the object on a plane and showing the “sectional view”. We have “dimensioned” the object in the isometric drawing in figure 7.
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. Which views should one choose for a multiview drawing? The representation of the object in figure 2 is called drading isometric drawing.
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.
A complete set of dimensions will permit only one interpretation needed to construct the part. We hope you like the object in Figure 1, because you’ll be seeing a lot of it. Before we get started on any technical drawings, let’s get a good look at this strange block from several angles.
Engineering Drawing and Sketching
The total length is known because the radius of the curve on the left side is given. The purpose of this guide is to give you the basics of engineering sketching and drawing. These drawings are easier to make than isometric drawings. This drawing is symmetric about the horizontal centerline. This is how the remaining rear section would look.
If the isometric drawing can show all details and all dimensions on one drawing, it is ideal.
Then imagine removing the material from the front of this plane, as shown in figure The dimensions should be placed on the face that describes the feature most clearly. There are many times when the interior details of an object cannot be seen from the outside figure 8.
The cross-section on the right of figure 22 is technically correct. Any darwing drawing should show everything: Dimensioning should follow these guidelines.
Diagonal lines cross-hatches show regions where materials have been cut by the cutting plane. When there is limited space, a heavy black dot may be substituted for the arrows, as in figure When the left side of the block is “radiuses” as in figure 30, we break our rule that we should not duplicate dimensions.
One form of cross-hatching may be used for cast iron, another for bronze, and so forth.