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What is the technical drawing. Why it serves?

## We can say that the technical drawing has the mission to shape in paper the physical reality of an object in the space. Therefore, we are going to be able to have the details of a piece, that being three-dimensional, we are going it to represent in two dimensions (the paper), but to be able to understand all to us (as it happens with the grammar rules) we needed a common criterion and that next to other things is what we are going to see in this subject.

1º Formats of Paper

The formats are standardized (that is to say, with values already defined).  According to what we want to represent we needed a great paper but or but small. All we know but famous, A4, but are also others but the great as A3, A2, A1 or the A1 and but small, the A5, A6.

The A4 has some measured of 210 Xs 297 mm and this yes we must know it. The rest has its measures (already we shelp that they are standard) but is a little heavy to learn so many values. If embargo, exists a relation from one to others, so that the union of two generates following format 2, that is to say, A4, it generates a A3 and a A4 divided by two half A5 generates. The figure down imagines what tenth

Types of Pencils

## We classify the pencils on the basis of the hardness of the graphite mine, so that a scale settles down from largest to smallest hardness. In the process of the drawing, we have several phases, being the initial (we worked with rough draft) where we were mistaken but and therefore we needed a pencil that we can erase easily. If the work is definitive, we can use a pencil with greater hardness Next we represented the hardness of the pencil and its reference H-B

The square and the triangle

They are two plastic groups with form of triangles very used for the works of technology. The square has two angles of 45 and one of 90 Triangle one of 90, orto of 30 and another one of 60 With the two, we can draw up straight lines with certain slopes on the horizontal and for it, we are going to carry out the following tasks.

Activity 1: Using the square and the triangle, to draw up straight lines that have the following angles on a horizontal: a) 30º, b) 165º, c) 135º, d) 120º and d) 75º Solutions

## Also they are very useful to do parallel and perpendicular. The following video shows as doing them

Scales

Scale to the mathematical relation is called that exists between the dimensions of a real object and the represented ones in a drawing. They imagine in the form of reason where the first term both indicates the value in the drawing and the second (after points: ) the value in the reality, of this form, the scale 1:200, means that 1 cm of the drawing is equivalent to 200 cm in the reality, that is 2 meters. But also we have the scale 200:1, which indicates that 200 cm in plane are 1 cm in fact. This is used to represent objects that are very small (details of a chip)

### Exercises: 1º  Do Whichever meters have a bridge if from the home in the end we measured in plane 12 cm and the scale is 1:500? 2º Just like previous if the scale is 2:800 3º the Whichever square meters have a football ground if the scale that we used is 1:100 and the dimensions of the field are 15 Xs 25 cm

Cutting system

It is not going to allow the geometric representation of the elements in bidimensional the three-dimensional space on the one (plane) and for it we are going to use a one orthogonal projection on a plane To the left we have three views. First of them on a vertical plane who we called cash settlement, 2ª on the plane of down that we called plant and the third lateral one that we called profile. Certain norms exist some to represent each seen We imagine letter L in the space. Since we have seen before, we have three views (to see the right) we phelp attention in which each of them is in a quadrant of the coordinate system, so that the plant is down, the cash settlement arrives and the profile at the right. Each of them is related to the neighbor by means of some reference lines, this is if the L has a width X sight from above, also has it sight of from the front and for that reason those discontinuous lines exist. The same happens with the view plants (h) and the profile (l) where by means of lines to 45º it indicates to us that it parts of the equal letter are sight from above that of profile. In order to initiate the system of representation of a piece in the plane, we will begin by this simple video

## Exercises cutting system

System of levels:

• When we represented a piece in paper is necessary, in many case, to know the dimensions the same and, for it, we have some norms that we must take to end to reflect the dimensions in the Components of levels: In the image of the right we have a partially annotated piece with the parts of a level that are:
• Line of level: (2) it comes represented by the parallel line to a side of the piece and marks the distance that we want to measure
• Line of extension (4): Line realised in fine section that prolongs the sides of the piece to be able to use the line of level. The idea is to remove the landmark outside the piece, so that it does not interfere with the own lines of the piece
• Number of level (3): Number that indicates the dimension of the part of the annotated piece
• You shoot with an arrow of home and end (1 and 5): They represent the home and the end of the level using you shoot with an arrow

Symbols: Additional graphical references used to give extra information of the level, for example Ø indicates that it is the diameter or R that is the radius of a circumference:

The landmark of a piece must contribute the complete information of its measures and, therefore, it must contain the right levels. It does not have to appear superfluous information (if a measurement is obtained as sum of two levels, it is not necessary to put 3º)

Activity 1: In the example of above, specifying if the landmark is correct and if lack some level

Activity 2. In the figure 1 and figure 2, to realise the landmarks necessary to define the pieces appropriately. Solutions: