What is Machine Sketching?
A machine sketch is a quick, freehand drawing of a machine or part of a machine.
For engineers, the ability to make quick, clear, and accurate machine sketches is very important.
Sometimes, a drafter or shop foreman might need to quickly sketch a broken part of a machine that can’t be taken out right away without stopping the machine. A construction engineer may need to quickly sketch new parts or fixtures when something doesn’t fit right during a project. A bridge engineer might need a sketch of a special part that’s missing or broken, to keep the work going.
All machine designs start in the mechanic’s mind and need to be drawn on paper before a full technical drawing can be made. Being able to sketch quickly is essential in these situations. Someone who isn’t experienced with sketching may find it very difficult when they need to make a sketch fast.
Paper to Use
Sketches are usually done on scratch paper or a notebook. Graph paper is really helpful because it makes it easier to draw quickly and accurately.
Types of Drawings
Like in a detailed machine drawing, a machine sketch usually shows multiple views (top, front, and side views, for example) of the machine or part. These views are basic projections of each other, just like in working drawings. Don’t add extra views unless you really need them to explain the design clearly. Two views are often enough.
Pencil and Sketching Style
For sketching, use a soft pencil, like an H or 2H, so the outline of the part stands out clearly from the dimension and section lines.
To draw lines, use short, overlapping strokes. This method creates a ragged line but helps you draw a straight line more easily than if you tried to draw a continuous one.
Size of the Drawing
Since machine sketches are often made quickly and in tough conditions, they usually aren’t to scale. Instead, measurements are used to show the size.
If you’re using a small notebook and need to fit two views on the page, first estimate the length and width of the part. Then, block out the spaces for the views in a way that uses as much space as possible. Measure the length of the object with your pencil and use your thumb to mark the length. Hold the pencil horizontally and about 1 foot from your eye, then use that distance to sketch the machine parts in their right sizes.
How to Make a Machine Sketch
To sketch quickly and accurately, follow these steps:
- Decide how many views you need and which ones to include.
- Estimate the length and width of the machine and divide the page into sections for the views.
- Start sketching the outlines of all the views at the same time. Don’t finish one view before moving to the others. As you draw one line on one view, draw its projection on the other views. This way, all the views get finished at about the same time.
- Add in the dimensions, auxiliary lines, and section lines. It’s important to add dimensions while you’re drawing so you don’t forget any important details later.
- After the sketch is done, go over the outline with a heavier pencil so it’s easy to see.
- Measure the machine with calipers and a ruler to check the dimensions already written on your sketch. Be sure to include the overall dimensions as a final check.
- Don’t forget to add any helpful notes.
Shortcuts to Save Time
To speed things up, you can use these shortcuts:
- For familiar shapes, like wheels, you only need to draw part of the object (like the hub, two spokes, and part of the rim).
- For symmetrical objects (like gate valves), draw just one-half of the object along the center line. You can finish the other half later if needed.
- For objects symmetrical around two center lines, it’s enough to draw only one-fourth of the object.
- If you can’t show details clearly (like bolts, holes, or fasteners), use notes to explain them. For example, write “3/4” drill” or “3/4” x 10 pi. tap” instead of drawing the detail.