How Do You Make Carbon Brushes?

carbon brush manufacturing

 Carbon brushes are an essential part of all power tools, but how are they made?

In this post, we'll discuss the major steps involved when manufacturing carbon brushes.

Need a new carbon brush? Browse our range here.

Pre-Step: What are Carbon Brushes and what do they do?

 Carbon brushes are a wearable part found in power tools that conduct electrical current between stationary and rotating elements inside a motor or generator.

Carbon is used as it conducts electricity well, but it's also soft enough to give a consistent contact point.

However this means they wear over time, and so you need to replace them once they become too worn.

Learn more about carbon brushes here.

finished carbon brushes

Step 1. Creating the Carbon Block – The Right Material is Key

 The first step in the process is to make the block of carbon, that this batch of brushes will be cut from.

The block is a combination of materials, specifically designed to a resistance that matches the voltage and wattage of the power tool they're going to be used in.

Power tool brushes will typically use a carbon-graphite mix, but other materials used can be copper graphite, silver graphite, natural graphite, and electro graphite.

Step 2. Design the Carbon Brush & Cut to Size

 The carbon brush has to be designed to fit a specific power tool, and so you need to ensure it meets the exact dimensions of the carbon brush holder it's going into.

 This involves making the drawings and cutting it to the exact size.

Step 3. Grind the Brush Body Until Smooth

 It's important to have a consistent contact point, so the brush must be grinded until it has smooth edges.

Step 4. Measure the Brush Body to Check Specs

 This is a final precuation to ensure the brush still meets the specification. A negative tolerance between -0.1mm and 0mm is acceptable.

animation showing the production of carbon brushes

Step 5. Make a Hole in the Carbon and Embed the Wire

 To create the connection to the static part of the tool, we need to embed a wire within the carbon brush, so at this stage we drill a hole into the carbon brush and add the conductive wire.

carbon brush conveyor belt

Step 6. Weld the Wire to the Terminal

 Finally we need to weld the terminal to the end of the wire, to ensure it can properly connect to the power tool system.

Some brushes not only have just a wire and an end terminal (like a push on spade connector), but also have a spring design which needs to have the right tension, length, diameter and thickness, to ensure the carbon brush has the right pressure against the Commutator. So the spring design part of a carbon brush must also be considered when making the final product.

measuring carbon brush springs

Don't Use Carbon from Old Batteries

 There are some rumours and tutorials onine where people are using carbon from old batteries to create carbon brushes.

This is very dangerous, and can damage your tool, because the carbon used is far too hard.

It's much better to purchase new brushes instead.

What does a poorly made carbon brush look like?

Typical characteristics of a poorly made carbon brush are:

  • Uneven edges.
  • Softens and breaks down while under heat.
  • Causes blackness in the carbon brush holder.
  • Smells like burning rubber.

If you're looking for a high quality carbon brush, shop our range online here.

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