Name: Engineering Drawing by mf Cousins
Author: MF Cousins
Publication: Cambridge Instrument Company Limited
Category: Engineering Books
Size: 12 MB
Format: E-Book (PDF)
Total Pages: 346
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Summary : Engineering Drawing by mf Cousins
In Chapter 4 you made some drawings, but although the outline was completed the drawings as a whole were unfinished because no dimensions were added. It will be realized that dimensions on a drawing are sometimes more important than the outline itself. With this in mind, dimensions must be placed in such a position as to convey their importance to the reader of the drawing. As every drawing is different in its conception, so the system of placing dimensions varies.
2 Summary : Engineering Drawing by mf Cousins
In order to learn how to dimension, the sketches with their dimensions must be carefully copied, together with the printed heading. You should make use of the knowledge gained in the preceding chapters, and although you are copying the sketches it is important that you should draw with construction lines only in the first instance, and then complete the outline, making use of the over-run construction lines as dimension lines. The first and very important thing to remember about dimensioning is that.
3 Summary : Engineering Drawing by mf Cousins
It should not be necessary for the craftsman to have to do any calculations in order to make the particular object. You will notice in Fig. This break illustrates that the object is too long to get on to a drawing and therefore the dimension gives the important information. It can be well imagined that instead of the part being 7 in. long it could be 7 ft long, but in either case it is the dimension that must be read. The end elevation shows the dimensions very
clearly so that from the drawing the part could easily be checked on a stock list of material.
4 Summary: Engineering Drawing by mf Cousins
The drawing is shown both in first angle projection and in third angle projection and it is of a bar of material § in. X \ in. X 2 in. long with a slot at one end J in. wide X ^ in. deep. The reason for this is that if a dimension needs to be changed during manufacture, then the draughtsman making the alteration to the drawing knows it has to be found in one position only and needs to be altered in that position.
5 Summary: Engineering Drawing by mf Cousins
A general observation on dimensioning is that a dimension must be placed where the well-trained person would expect to find it. It is very important to notice that only detailed parts are dimensioned fully, and that assemblies, or assembly drawings, including sub-assemblies, are never covered with hundreds of dimensions. The only dimensions that should appear on an assembly drawing are the major overall dimensions, such as height, width and length, or a few specification dimensions that would be required if a certain machine were being purchased.
This, then, can now be filled in in outline. Again turning the object in the front elevation one angle to the left through 90° will give us a reversed L end elevation, C. If you take the object in elevation and turn it through 90° towards you, you will get the plan, B, which can be shown in outline. For correct projection the two ports must be shown in hidden detail in both the end elevations and the plan.
PUBLISH ID: LP342EB
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