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How to Choose the Right Material for Your CNC Part

How to Choose the Right Material for Your CNC Part

Choosing the right part material is an essential part of planning your project. The material you choose influences the production costs, lifetime usability of the parts, and the overall functionality. 

Our machining processes allow us to create custom parts using nearly any material. Some materials are easier and cheaper to machine than others, but there are a few factors that can help you make the right choice. If you’re still not sure, you can always reach out to our team for help.  

Here is a quick overview of some different material options and how you can choose the best one for your project. 

What will the part be used for?

The first step in the process is to figure out what the machined part will be used for. Some parts, like those used in aircraft, need to be lightweight and able to withstand pressure. In other cases, using a polycarbonate part is best to reduce weight. 

If your parts are going to be exposed to water you’ll need to use stainless steel rather than carbon steel. And if your parts need to conduct electricity well, copper may be the best choice. Metal alloys react differently to high temperatures, and some expand and contract more than others. Knowing this will help ensure the parts will function properly when they’re in use. 

Elements like stress load, tolerance, and types of fastening (welding, rivets, etc) also impact your material needs. And you’ll want to consider specifications for military and aerospace parts, or government regulated food and medical environments.

Each material has it’s own pros and cons. The more you know about how your part will be used and the environment it will be used in helps choose the right material. 


Today, there are hundreds of different metals and alloys used for CNC machined parts.

Each metal, alloy, and grade contains different percentages of elements. Sometimes, the differences are only a few percentage which can make a significant difference. For example, there are 5 common grades of Monel. Each grade has similar amounts of Nickel and Copper, but there’s 2-5% of Silicon, Aluminum, Titanium, or Sulfur added. This makes the different grades easier to machine, more resistant to corrosion, or better conductivity. 

In general, lighter and softer metals like copper and aluminum are easier and faster to machine. 

Machining aluminum parts can be done 4-5 times faster than machining carbon steel parts. And machining hard stainless steel can take twice as long as carbon steel. 

The prices of different metals also vary significantly, even for a different grade of the same metal. For example, a bar of 7075 aluminum can cost 3-4 times more than a bar of 6061 aluminum. 

The more expensive metals usually take longer to machine, which further adds to the manufacturing costs. In some cases, the higher strength or corrosion resistance is necessary. And the more expensive materials tend to last longer, which can reduce the lifelong cost of the part. 

At Spex, we have the capabilities to machine any type of metal. We can plate or anodize the metal which increases the durability and improve wearability of the part. 


Plastics and polycarbonates can be a great alternative to metal parts. These are much lighter, easier to machine, and less expensive than metals. Some polycarbonates are also more resistant to certain chemicals that corrode metal. 

Of course, plastics can’t always replace metal parts. They’re usually less heat resistant, and can’t withstand as much pressure or friction. Most plastics are also not the best option if a tight tolerance is needed. If you need a lightweight part that doesn’t need to be super strong, this can be a good option to reduce costs. 

Plastic also offers the benefit of rapid prototyping. We offer rapid prototyping using a 3D printer. This can give you the feel of the actual part or assembly without needing to machine a metal part. Even if your project requires metal, plastics play an important role in the design process. 

3 things to consider

Weight: Does the weight of parts influence the efficiency of the assembly? Generally, aluminum is a strong and lightweight material that’s suitable for most environments. It’s about 1/3 of the weight of stainless steel. 

Strength and resistance: Is the part going to bear weight? If so, you’ll need to use a stronger material to avoid part damage. If your part is going to be exposed to harsh chemicals like gas, oils, or saltwater, you’ll need a material with high corrosion resistance. You’ll also need to consider how the material is affected by temperature changes. Different metals expand and contract at different temperatures. 

Cost: As mentioned earlier, the costs of different materials can vary by 2-30x. The costs of raw materials, machining, and how long the part will last are all important. Specialty materials like superalloys are going to be more expensive, but they also last much longer in harsh conditions. 

If you have questions about picking the right material, don’t hesitate to reach out to our team. We have worked on thousands of custom projects in a range of industries. We are happy to help you pick the best material based on your specific needs. 

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Talk with one of our team members if you have any questions about choosing the right material for your project. 

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Phone: (585) 467-0520

Email: sales@spex1.com

85 Excel Drive
Rochester, NY 14621