Introduction: Inside the Engineer's Notebook- a Guide to Pictorial Sketches

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First of all... a pictorial Drawing is a 2 dimensional illustration of a 3 dimensional object, it shows 3 faces of an object in one view, and it provides a realistic view of an object. There are Three types of pictorial drawings: isometric drawings, oblique drawings, and perspective drawings. We will go through all 3 of them. You might be asking yourself, why should I be reading this? what use does this have for me? and when will I use it? Well, It actually is used quite often in the engineering, inventing, and product designing worlds. Which, I would tend to think, DIY fits nicely into. So, you should be reading this, because, well, it is good information to know, it can come in very handy if you ever start getting into professional engineering or other similar things. What use does it have for you? It provides you with a lot of valuable information that could be useful later in life, you never know. Lastly, when will I draw pictorial sketches? Welp, if you are a professional engineer, then, all the time, or if you want to manufacture something, etc. This is not an extremely detailed guide on pictorial sketches, but it is an intro to it, meant to get you started into it.

I would have to also recommend that you ALWAYS use a ruler and graph paper.

Step 1: Definitions

Before you get started reading this guide, there are quite a few helpful terms that will help you understand the text a little bit more:

Construction lines- light, thin lines used as guidelines to draw the objects (kind of like the rough draft)

Object lines- thick, heavy lines that represent the object's edges (sometimes refered to as "heavy in" the lines, I use both terms)

Hidden Lines- Lines that are hidden by a face (usually in a multi-view drawing) (e.g. a hollow box or a pipe would need hidden lines to show that they are hollow) (hidden lines are dotted or dashed)

Glass box (or box method)- a way to make oblique, isometric, and perspective drawings

Face- a plane or side of an object

Vanishing point- the point in a perspective drawing where everything disappears (vanishes), and where your lines lead to.

Horizon line- The line in a perspective drawing that the vanishing point rests on

Width- an objects side to side dimension

Height- an objects top to bottom dimension

Depth- an objects front to back dimension

Step 2: How to Select a Front View

You can select the front view usually pretty easily, you just have to find which side of the object satisfies the most of the following:

  • Most natural position or use
  • Shows the best shape and characteristic contours
  • longest dimension
  • fewest hidden lines (more on this later)
  • most stable and/or natural position

Step 3: Tonal Shading

Tonal shading/shading is not a hard concept to grasp, but I figured it was important enough to go through. It's pretty simple, though not totally realistic. Basically, say there is a north, south, east, and west facing faces. Then there is the top and bottom. Light always comes from above, so the top faces are always white (not shaded in at all) and the bottom is always the darkest (though most of the time you don't see it). So, shading isn't super realistic because the faces do not cast shadows. So, you can decide what direction the light is coming from, and decide how each face will be shaded, all of the north faces will be shaded the same, all of the west faces will be shaded the same, all of the east faces will be shaded the same, etc. That is basically tonal shading in a nutshell.

Step 4: Oblique Drawings

An oblique pictorial starts with a straight on view of one of the object's faces, which is often the front face. Angled, parallel lines are drawn to represent the objects depth. Common oblique depth line angles are 30ᵒ, 45ᵒ, and 60ᵒ. There are a couple of different types of oblique drawings, there is cavalier, which uses the exact dimension of the lines for the depth, so if you are drawing an object that is 2 cm deep, then the depth line would be 2 cm long at its respective angle. While this gives you a more accurate depiction of the object's dimensions, it looks a lot more skewed and unrealistic than the other type, Cabinet. Cabinet drawings use depth lines that are half of the actual length of the depth line. This method makes it look much more realistic, while still allowing you to calculate the depth of the object.

To make oblique pictorials, it is best to use the "glass box" method, where you sketch an imaginary glass box surrounding the object, being as tight as it can be but still being a rectangular prism. I'm going to demonstrate (above in the pictures) by making a simple "L" shape. Here is a simple step by step on how to use this method:

1. Sketch the rectangle to represent the overall width and height of the front face of the "box". Make sure that the height lines are vertical, and the length lines are horizontal. This will give you a straight view of the front. (Picture 1)

2. Sketch the depth lines to the overall depth, completing the box. Remember to make your depth lines at either a 30ᵒ, 45ᵒ, or 60ᵒ angle. The most common and easiest angle to use is 45ᵒ because you can make a 45ᵒ angle on regular graph paper by just drawing from corner to corner. (Picture 2)

3. Sketch the points and construction lines to identify the edges of the object's faces that are on the outside surface of the box starting with the front face, then the top and side faces. (Picture 3)

4. Trace over the construction lines with object lines to delineate the edges of the object's faces that occur on the outside surfaces of the box. (Picture 4)

5. Using construction lines, create the rest of the edges occurring inside the box (as well as on the edges that aren't visible) to finish the shape. (Picture 5)

6. Trace over the construction lines that you just created with object lines to delineate the remaining lines. (Picture 6)

7. It is sometimes a good idea to add in shading for to differentiate the different faces.

Tip: When shading, the light always comes from above, so the top faces are never shaded, they are always left white. (Picture 7)

Step 5: Isometric Drawings

In an isometric drawing, the three faces will share 1 point, and each "2D" angle coming from that point will appear to be 120ᵒ. The height lines on an isometric pictorial are vertical (90ᵒ), while the depth and length lines will appear at either 30ᵒ, or 150ᵒ. The general orientation of an isometric view is viewing the top, front, and right side views. It is also highly recommended that you use isometric grid paper to do isometric drawings, it makes life a lot easier. We are again going to use the box method for isometric drawings.

1. Create the box using the height, width, and depth of the object (Picture 1)

2. Identify the outside faces and use construction lines to outline them (Picture 2)

3. Heavy in the outside lines to create your faces on the surface of the box (Picture 3)

4. Create the inside faces using points and construction lines (Picture 4)

5. Heavy in the inside lines to make the faces on the inside of the box (Picture 5)

6. Add shading (Picture 6)

Step 6: Intro to Perspective Sketches

Perspective sketches are the most powerful of the three types of pictorials. That is because it shows gives the drawing closest to what the human eye perceives it in real life, it is also the hardest to draw (though, I find it the most fun to draw). Of the perspective drawings, there are 3 types: 1 point, 2 point, and 3 point. The "# point" refers to the number of vanishing points that are located in your picture, 1 vanishing point is the least realistic (though still more realistic than isometric and oblique drawings), while 3 point is the most realistic of the three.

Step 7: 1 Point Perspective

1 point perspective is the least realistic of the three, but still semi-realistic (in complete honesty, I think that 1 point looks the most realistic, but supposedly 3 point is). 1 point is also the easiest to draw, as you only have 1 vanishing point. We will once again be using the box method.

1. First you need to draw a horizon line, you can place this anywhere on the paper, but the most common spot is above the top of the paper. (Picture 1)

2. Next you need to identify where you want your vanishing point to be, it can be anywhere on the horizon line, including off of your paper. (Picture 2)

Tip: The farther from the object you put your vanishing point, the more realistic your object will look, this goes for 1, 2, and 3 point perspectives

3. Draw a rectangle (or square) to represent the farthest extents of the front face of the object (like you would do in an oblique drawing) (Picture 3)

4. Draw lines from the four corners back to the vanishing point (using a ruler) (Picture 4)

5. Estimating the the depth of the object, draw a horizontal line between the two lines from the corners to the vanishing point to represent the back edge of the box, then from where that line intersects the line that goes to the vanishing point, draw a vertical down to the other line that goes to the vanishing point, to represent the back edge. Now you should have your box. (Picture 5)

6. Using construction lines, sketch the outside faces that occur on the surface of the box, and then draw lines from the corners on the faces back to the vanishing point. (Picture 6)

7. Heavy in the construction lines from step 6 (Picture 7)

8. Then fill in the remaining edges on the inside of the box, keeping the length and height lines at 0ᵒ and 90ᵒ, but making the depth lines all go back to the vanishing point. (Picture 8)

9. Heavy in the lines to delineate the objects edges to the lines leading to the vanishing point etc. (Picture 9)

10. Add shading (Picture 10)

Step 8: 2 Point Perspective

2 Point perspectives are kind of the middle man of the 3 (obviously), they are not the easiest to make, nor the hardest. They aren't the most realistic looking, nor the least. Despite being the middle man, 2 point is by far the most commonly used type of sketch, since it is not as hard as the 3 point, but it is still more realistic than a 1 point.

1. Sketch a horizontal line to represent your horizon line

2. Identify 2 vanishing points, one on each side of the paper

3. Sketch a vertical construction line somewhere in between the two vanishing points, the angle of the object will change depending on where your vertical line is. This line will represent the front edge of the object

4. Locate 2 points on the construction line to represent the top and bottom of the corners of the box (box method)

5. Sketch construction lines from each point on the vertical line to BOTH of the vanishing points

6. Sketch points and vertical construction lines to create the depth and width of the box. You should now have your completed box.

7. Sketch points and construction lines to identify the edges and faces of the object that occur on the visible surfaces of the box. MAKE SURE YOUR WIDTH AND DEPTH LINES POINT TOWARD THE VANISHING POINTS

8. Trace over the construction lines with object lines to identify better the edges of the faces on the outside surface of the box

9. Add construction lines and points to identify the faces and edges on the inside of the box. MAKE SURE ALL WIDTH AND DEPTH LINES POINT TO ONE OF THE VANISHING POINTS

10. Heavy in the construction lines to delineate the rest of the object's edges

11. Add shading

Step 9: 3 Point Perspective

3 point perspective is not very used at all, as it is quite complicated. For this reason I am not going to go over it. If you want me to make a step by step, then let me know in the comments, and I'll try to get it up.

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