3. Technical drawing I

3.- TECHNICAL DRAWING

3.1. Drawing tools



Ruler

We use a ruler to measure distances, usually is graduated in centimetres and millimetres (see chapter 1)


Protractor

We use a protractor to measure angles, you must place the vertex of the angle at the center mark of the protractor.
 

Pencil
 
Pencils have leads of different hardness in a scale that range from soft (B) to hard (H)

                  Sofest ...4B , 3B, 2B, B, F, HB, 14. 2H, 3H. Hardest

 If the lead is soft the lines will be dark and thick

To obtain dark, thin lines it is necessary to use soft lead and to sharpen the pencil  very often.
Rubber

Rubbers are used to erase what has been drawn with a pencil.
They also can be softer or harder.
tu Softer rubbers normally   erase better but they also wear down faster.


Compass

The compass is used to draw arcs or circles.
One arm of the compass has a needle. The other arm has a lead or a pencil.

Square and bevel

We use the square and bevel for drawing parallel and perpendicular lines and angles

CAD
(Computer Aided Design)

These computer programs are used to make technical drawings for architects and engineers



3.2 Basic Drawing Techniques


Making parallels with a square and a ruler
You will need two squares or a ruler and a square:
Making perpendicular lines with a square and a ruler
You will need two squares or a ruler and a square:
Drawing angles with square an bevel


Notice that the squares have some angles that you can use to draw angles on your paper.


You can draw directly the 90º, 45º, 60º and 30º angles, you only have to draw two lines, one on each side of the angle corner.


You can also combine different corners of the different squares and obtain angles which are the sum of the corner angles.


3.3.- Activities 

Activity 1 : Visit the following web page: 


Look at the drawing equipment and do the first set of exercises.

Activity 2: Using two square and bevel, draw parallel lines.

Activity 3: Using square and bevel, draw perpendicular lines.

Activity 4: Using square and bevel, draw the following angles.

60º  55º  120º  135º  

Watch the animations on how to draw a 60º angle (pressing next or run Then, using a compass and a ruler, draw a 60º angle on paper.
Draw the construction lines thin and draw the segments that form the angle lines thick.

Activity 6. On the same page (http://www.mathopenref.com/constangle6o.html)
watch the animations on how to draw 45º and 30º angles and then draw them on paper.