Introduction: Technical Drawing in Three Dimensions

This Instructable will demonstrate the steps necessary to draw in a technical format a part or object in three dimensions. Technical drawing of this format is typically used by engineers or architects to help visualize components or products they are designing. This process is being done more often now using computer programs, however it is still an important skill to have for quick visualization.

For this Instructable, a generic shape with some curves and holes is drawn so that the process for drawing curves and holes can be explained. These are common part features, so understanding the process in drawing them is important. Once the process is understood, it can be used and altered to suit the user’s needs in other drawings.

Step 1: Tools

The basic necessary tools are as follows:

Ruler or Straight Edge – A good ruler or straight edge will ensure straight and crisp lines in the drawing. Plastic or metal will work and it is important to check the edge of the ruler to make sure it does not have any dings or chips as this will cause the lines to become wavy or broken.

Pencil – Choosing a proper pencil is important. Mechanical pencils are generally preferred as it does not require frequent sharpening to maintain a fine point. Choose one that uses the smaller 5mm lead rather than 7mm for sharper lines. If not using a mechanical pencil, it is recommended to use a pencil with HB lead. A softer lead will lose sharpness at the tip faster than a harder lead.

Eraser – Normally a mechanical pencil will have an eraser on the end and this will be suitable. Art stores also have various other kinds of erasers that also will work fine.

Eraser Shield – A thin piece of metal with different slots and holes cut into it. This is useful for erasing because you can shield lines you want to keep while erasing the lines you do not need. This is not a critical tool to have but can save time from having to touch up lines that are inadvertently hit with the eraser.

Protractor – A very useful tool for drawing circles. Circles are difficult to draw by hand so using a protractor can help substantially. Unfortunately it can only be used to draw circles that are in a two dimension plane and not those that are shown at an angle from the viewer (as will be seen in this example).

Paper – There are many different kinds of paper available for drawing, from thick artists sketching paper to normal printer paper. For this Instructable printer paper is more than sufficient, however in a professional environment special papers are more commonly used.

Step 2: Drawing the Title Block

The title block is a distinguishing trait of technical drawings. There are many different formats of title blocks, but the one chosen here consists of seven blocks:

1. Title: Positioned in the center of the main title block and has the name of the drawing.

2. Project: In the upper left portion of the title block and has the name of the project to which the drawing is associated.

3. Date: In the far lower left and has the date of when the drawing was made.

4. Scale: In the near lower left portion and has the scale of the drawing. Putting N/A or Not Applicable indicates that no particular scale is used for the drawing.

5. Name: In the upper right area and has the name of the name of the drawer.

6. Page: In the far lower right and indicates which page this drawing is by the first number and out of how many drawings by the second number.

7. Rev (Revision): In the lower near right and has the revision number or letter if multiple different copies of the drawing exist.

Step 3: Drawing the Three Primary Axes

To begin drawing the part, you first setup the three primary axes; x, y, and z. The z-axis is typically chosen as the vertical axis while x and y are the two axes at an angle from the horizontal. The angle between the horizontal and the x and y axes can vary but 30° is common and is shown here. The three axes should start at a central point, called the “origin”, and can be extended lightly over the entire drawing region. The lines are darkened here only for ease of viewing.

Step 4: Draw Main Cube

After the primary axes are drawn, lightly sketch a box outlining the object and where it will be drawn. This is a box that the entire object will fit into once finished. The box will share at least some common lines with the object along the exterior. Those that will not be shared will be erased later on.

Step 5: Draw Straight Exterior Edges

Now start to draw the exterior edges of the object. Remember to keep lines parallel to their respective axes unless the part has an angle such as the example drawing. The slope in the middle of the part is supposed to be at an angle and so does not remain parallel to the axis. Approaching lines such as these will require the lines that are parallel to the axes to be drawn first. This ensures that the angled line is at the correct length and perceived angle.

Step 6: Draw Curved Exterior Edges

To draw a curved edge, first enclose the curve in using straight guidelines as shown. Once enclosed in straight lines, draw light dashed lines following where the curve will be place. Take note that curves that come toward you have an obtuse angle to its center causing a wider curve, while the curves that point to the side have an acute angle to its center making it much shorter. Remember that since this is being done in three dimensions, you must show four curves, two at each height level, to maintain depth in the drawing.

Once the dashed guidelines are drawn, begin connecting the dashes to form a solid curved line. This approach is much easier than trying to draw the curved line right away, as that can take many attempts to achieve the proper curve. This method allows the curve to be broken into smaller increments making it easier to draw. Once the curve is drawn, erase the straight guidelines that enclosed it.

Step 7: Draw Square Cut Out

Creating a square hole in the base of this part is fairly straightforward. Outline the size of the hole on the top portion of the object. Once that is complete, drop a vertical line down to the depth of the part. Multiple lines can be drawn on all four corners, but from this view it is unnecessary as only one vertical line will be seen. After the cut out is drawn erase all guidelines used.

Step 8: Draw Circular Holes

To draw circular holes in the top part of the object, you need to take a few steps to set them up. First, draw two lines parallel to the top and with a distance apart equal to the diameter of the holes. The centers of the holes should be identified with cross-hairs. This also sections the circle into four corners so you can apply what you learned in step six. Next draw two squares around the perimeter of where the circles will be placed. Now draw dashed lines around the center of the circle with the desired diameter, as you did in step six. Finally, connect the dashes forming a complete circular line.

Step 9: Erase Unnecessary Lines

Now erase all the guidelines used for the circles or any of the previous steps that has not been done so already. Use the eraser shield when doing this to minimize having to go back and touch up lines that should be kept.

Step 10: Draw Hidden Lines

One final optional step is drawing hidden lines to show edges that aren’t viewed from the angle the drawing was done in. Hidden lines communicate to a viewer that the holes, cuts, and exterior edges do or don’t have any unanticipated features. To draw hidden lines, locate the center of the holes, edges of the cuts, and the adjoining corners of the exterior edges. Then, using a straight edge, draw a dashed line through the circle or from the corresponding edge/corner in the direction it should go. Be sure that the dashes are uniformly spaced and drawn appropriately. Also make sure the lengths or your hidden lines are reflecting the depth that they travel, if the cut goes through the entire object then the hidden lines need to show that.