Dimensioning

Types Of Lines And Its Uses:

There are three types of types on the basis of thickness and they are:

• Visible Lines  ↝  It represents features that can be seen in the current view.
• Hidden Lines  ↝  It represents features that cannot be seen in the current view. 
• Center Line  ↝  It represents symmetry, path of motion, centers of circles,, axis of asymmetrical parts.
• Dimension and Extension Lines  ↝  It indicates the sizes and location of features on a drawing.

Placement Of Dimension Lines:

1. Dimension should be outside the view.
2. Dimension should be applied to one view.
3. Dimension should be placed in a view that shows the distance in its true length.
4. Dimension lines should be placed, in general 10 mm (1/2 in) away from the outlines from the view.
5. Parallel lines should be placed uniformly.
6. Values should be midway (auto centered) between the arrow heads, except when a center-line interferes.
7. Dimensions arranged in continuous form are preferred upon readability.
8. Place a longer dimension line outside a shorter one.
9. Dimensions should never be crowded.  
10. Angular dimension should be outside the view.
11. Dimension Text should be in between the dimension lines or to the right of dimension lines.
12. Dimension lines has a minimum spacing of 4 mm.
13. If a view is very small then an arrow head used to show the dimension of lines. These arrow heads are filled or closed or opened.
14. If arrow head comes in between the dimension line, then it break the previous dimension line.
15. Avoid dimensioning to dashed lines if possible.

Types Of Holes:

There are five types of holes and they are:

1. Through Hole
2. Blind Hole
3. Drilled and Counter-bored Hole
4. Drilled and Counter-sunk Hole
5. Drilled and Spot-face Hole

References:

• Videos from youtube.
• Images from google images.
• GIF: https://www.mathwarehouse.com/animated-gifs/conic-sections.php
• Materials from my university notes, Engineering Drawing Textbook by N.D. Bhatt.