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Fig. 59 Methods if indicating tolerances. Fig. 60 Dimensional tolerances do not necessarily ensure geometric accuracy. as the use of a fraction implies the general drawing tolerance. You will always find this on production engineering drawings in the title box in terms such as Tolerance 0.02in. except where stated or Tolerance on all fractional dimensions 1 64 or Tolerance 0.05mm except where stated. To sum up this section, it is important to realize that setting...

Right Side View

Fig. 90 The planes of projection in 'Third Angle. Fig. 90 The planes of projection in 'Third Angle. Current standard sizes of drawing sheets are based on a sheet which is nominally one square metre in area, each smaller size being one half of the previous one. The sizes are as follows

As

Screw thread, and those not accustomed to it may be confused especially when shown in hidden detail. I have the further objection to it that to the amateur drawer-reader it can be confused with a shaft bearing two flats see sketch (m). For all my own drawings I use the first method, (a, b, c). It is very clear, particularly in hidden detail, and I don't find it difficult to make a presentable job of the outline. I do use method (h) occasionally, but never in hidden detail, as the drawing...

Introduction

It is perhaps significant that the use of 'drawings' for communication preceded the development of 'writing' by tens of thousands of years. This is not really that surprising, as a single sketch can convey data that might need hundreds of words -Fig.1. Furthermore, a well-executed drawing is far more precise than words try describing a 3-throw crankshaft in words alone with sufficient detail to enable it to be manufactured. The use of drawing for such technical matters is at least 4,000 years...

Developments and Intersections

This is an aspect of workshop drawing that often arises when, for example, we need to cut out sheet metal which can be rolled into a specific shape, or when we need to cut a hole in a container - boiler or tank -which will be a close fit to a branching piece. A development is no more than the shape of the piece of sheet in the flat before folding and jointing. An intersection is the profile of the curve formed when two sections meet. You will find six of these on every nut where the cone of the...

Tolerances

There is some confusion over both the nature and purpose of tolerances on dimensions. In particular, many people speak of a tolerance when they mean an allowance. An allowance is the difference between the dimensions of two mating parts necessary to allow them to work. Thus a shaft may be 0.03mm or 0.001 less in diameter than a bush, to provide a sliding fit, or the same amount larger than the hole to result in a drive fit. This allowance emerges automatically when the part is dimensioned, and...

Making Drawings and Sketches

You can, of course, make a perfectly usable drawing with a felt pen or a piece of chalk. At the other extreme you may have seen drawings being produced on most elaborate draughting machines coupled to electronic display units. So, a few words on the types of drawing before dealing with how to make them. I will start with the sketch. This is used for three main purposes. (1) To record an idea so that it is not forgotten later. (2) To record the measurements or shape of an existing piece of...

First Angle Third Angle

Fig. 17 The international symbol indicating the projection system. This should appear on ALL drawings. then, I have had 70 years' experience of reading drawings, many very complex indeed. But such an arrangement is just not fair on the less experienced. The second example I have copied in Fig. 16A, but have left out the dimensions. This one may present no problems in reading, but there is no reason at all why the three views should not have been set in correct projection - either first or third...

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Fig. 69 Pencil points, a for linework b for figures and letters c for compasses. You can obtain these in the classic wooden form, or as refillable holders. Again tastes differ -1 find the collet-type holders a bit of a nuisance as if you have several grades it is difficult to tell which is which, whereas the wooden ones are clearly marked at the end. Make your choice The critical matter is the sharpening. For all linework the 'point' should not be pointed, but more a chisel shape, Fig. 69 a ....

Conventional Representation

To draw every part of a workpiece in full detail would be very time-consuming and would also be likely to make the drawing less readable. This particularly applies to parts that are often repeated, such as screw threads. Over the years, therefore, draughtsmen have developed many conventions or symbols to replace the detail representation of the feature these have gradually been standardised on a more or less international basis. I have already dealt with those referring to the sectioning of...

The Theory of Orthographic Projection

Projection Box Orthographic Drawing

The fundamental theory is rooted in the principles of solid geometry and need not concern us. The basic idea, so far as drawing is concerned, is that there are three planes mutually at right angles, like the sides of a box. The views are projected onto these planes which are then developed or opened out into a flat sheet - the paper we draw on. In first angle projection, Fig. 89, the object with faces A, B and C visible, is imagined to be suspended inside such a box. Three of the sides are...

Info

Fig. 21 'Trimetric projection, using a special square Fig. 23 , gives a more natural pictorial effect. The system can provide alternative viewpoints, as shown. From the instruction book to the Trimetric Square . Fig. 21 'Trimetric projection, using a special square Fig. 23 , gives a more natural pictorial effect. The system can provide alternative viewpoints, as shown. From the instruction book to the Trimetric Square . differently each time. Fig. 22 is another example, showing how a change in...

Metric and Imperial Drawings

The translation of a metric drawing to imperial dimensions presents little difficulty, as the amended dimensions would be in decimal inches, and these would imply the same degree of precision as on the original thus 26mm could translate as 1, or as 1.02 or depending on the class of work. Translating from inches to mm differs, however, as many designers still use fractional dimension rather than decimals, and some even work in sixty-fourths. If such fractional dimensions are toleranced the...

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Beginners in the 'art and mystery of turning' for example. But it is quite wrong to leave anything off the drawing, even if it means setting a fairly comprehensive note in the title box at the bottom. If the workshop drawing includes a number of parts, then reference numbers and a list in the title box should show the name of each, either immediately underneath it or. It should not really be necessary to say so but it is important to state the material of which each part is to be made, and the...

Director Of Finance

Fig. 87 In this intermediate stage, all dimmensions have been converted to metric but to three places of decimals. increase Dt, as a little, as we decreased D. This brings the reference dimension, originally 44.45mm, to 45mm. Again, a convenient round figure. Turn to the crankshaft. The outer faces of the two webs determine the shaft location, D3. Make this 64mm for trial. Then, if the crankpins are made 16mm wide the big end bearing can be machined to suit and the webs made 5mm thick the...