PRIN. OF DRAFTING AND SHOP DRAWINGS - OD1641 - LESSON 1/TASK 2
b. T-Square and Triangles. A T-square is used as a guide for drawing horizontal
lines and as a support for the triangles which, in turn, are used as guides for
drawing vertical and inclined lines. To use a T-square or triangle as a guide for
drawing lines, pull the pencil along the edge of the straight edge from left to
(These directions are for right-handed people.
Left-handed people should
reverse the directions.) Rotate the pencil as you draw so that a flat spot will not
form on the lead.
Flat spots cause wide, fuzzy lines of uneven width.
remember to keep your drawing lead sharp.
When using a T-square, hold the head (top of the T) firmly and flat against the
left edge of the drawing board. Use your left hand to hold the T-square still and
in place while you draw. When you move the T-square, always check to see that the
head is snug against the edge of the drawing board before you start to draw again.
When a T-square and a triangle are used together to create a guide for drawing, the
left hand must not only hold the T-square firmly in place; it must also hold the
edge of the triangle firmly and flat against the edge of the T-square.
accomplish this, use the the heel of your hand to hold the T-square in place and
your fingers to keep the triangle against the T-square.
It is important that all your tools be accurate.
A T-square, for example, must
have a perfectly straight edge.
If it does not, you will draw wavy lines and
inaccurate angles with the triangles.
To check a T-square for accuracy, draw a
long line by using the T-square as a guide. Then flip the T-square over and, using
the same edge just used as a guide, see if the T-square edge (now upside down)
matches the line. If it does not, the T-square is not accurate.
Triangles should be checked for straightness in the same manner used to check a T-
square, but, in addition, they must be checked for "squareness." To check a
triangle for squareness, align the triangle against the T-square and draw a line by
using the edge of the triangle which forms a 90, angle to the T-square as a guide.
Holding the T-square in place, flip the triangle over, and see if the triangle edge
matches the line. If it does not, the triangle is not square, meaning either