Introducing engineering
Introducing engineering

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4.7 Joining our gearwheel

Whilst we cannot make our food mixer gearwheel just using joining processes, we could make it out of several pieces that could be joined together.

Activity 36 (video)

Watch Videos 5 and 6 of laser welding gears and press-fitting differential gears. As you watch, think about how much easier it is to make the teeth on a gearwheel if they can be formed on a separate ring that is joined to the body of the gear in a separate operation.

Download this video clip.Video player: Video 5 Laser welding gear components (1 minute)
Video 5 Laser welding gear components (1 minute)
Interactive feature not available in single page view (see it in standard view).
Download this video clip.Video player: Video 6 Adhesive bonding of differential gears (1 minute)
Video 6 Adhesive bonding of differential gears (1 minute)
Interactive feature not available in single page view (see it in standard view).

In practice, any of the joining processes (soldering, adhesion and welding) would allow the wheel to be built up from bits. Wooden gearwheels and waterwheels used in mills many years ago, known as cog wheels, were made by joining together individual parts that could easily be replaced if any wore out after prolonged use. However, these were on a different scale from that of a gearwheel from a food mixer. So although building a gear would be possible, it is not really a practical proposition. At the extreme, imagine trying to build a gearwheel from parts; each tooth would need to be manufactured individually and then screwed, glued or welded together to the central ring. A great number of hours would be spent manufacturing each one.

Although the gearwheel itself is not suitable for being made through an assembly process, it is itself assembled into the food mixer, which has many discrete parts, made from a range of processes. There is always a stage at which a single product is likely to be assembled in some form into a larger product for a particular use.

Activity 37 (self-assessment)

Imagine you were making a large sculpture. List three reasons why you would make it in several pieces and join them together and three concerns you might have as a result of that decision.


Some of my reasons:

  • I could build the sculpture from smaller, more manageable components.
  • I could incorporate several different materials.
  • I wouldn't need the means to make the object in one piece.

Some concerns are:

  • Joints may be a weak point in the sculpture, and even welded joints will not necessarily have the strength of the materials that are joined.
  • I shall have to pay attention to surface preparation because this can affect the joint properties in many cases.
  • I'm not sure about the longevity of the sculpture.

You may have suggested other, equally valid, factors.

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