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CNC Machining Material Selection Guide

CNC material selection guide

Have a project with a great design? You’re off to a strong start, with the specs and prototype already finished. Now you are ready to start crafting your product. If you’re interested in using a CNC machine to manufacture the new part, you won’t be disappointed with your results, especially if you choose the proper material.

CNC machining has become a staple for a wide array of disciplines that need specialized parts manufactured for their projects. CNC materials have expanded to meet the demands of consumers, engineers, contractors and other fields to create solutions for very specific applications.

Having a variety of materials to choose from is a luxury, but it can also be overwhelming and confusing if you don’t analyze what your needs are and ask yourself some questions before making a decision. If you want your project to run efficiently and produce products that fit perfectly, this CNC machining materials guide can help you during your decision-making process.

Essential Questions for Selecting the Right Materials

Choosing the right materials for your part is the difference between mediocre outcomes and optimum results. These important questions are the best place to start. The more you can narrow down the CNC machining materials that would be the best fit for your part, the easier it will be to select a material that will suit your needs and be cost-efficient.. Here are some things you should consider.

How Will the Part Be Used?

Since CNC machining has expanded over the years, so have CNC machine components. Similar types of materials can be used for a variety of products and result in varying capabilities. Insulation is a great example. The materials used to insulate a Breathalyzer may be different from the materials that provide insulation in a camera. They’re both used for the same purpose, but not in the same way or for the same type of outcome. On the other end of the spectrum, materials for soundproofing walls have different specifications and uses as well. It's important to start with considering the end result of how your part will be used.

Outdoor Environment Vs. Indoor Environment

Outdoor and indoor environments are very different — one is completely dependent upon the weather, whereas the other has the ability to be a much more controlled environment. In outdoor environments, for example, you need to plan for moisture. Your material will need to be able to resist the effects of oxidation, such as rusting, in order to maintain its integrity over time. Rigid foam provides a great example of a material that resists moisture and rusting while also maintaining structural integrity.

Extreme temperatures, both high and low, will also eliminate certain materials as the best option. Or you may need to be able to meet code for FDA-regulated specifications. Where your materials will be and how they react to moisture and extreme temperature change becomes a cornerstone in deciding which one to go through with.

Stress Load

material stress factor

High stress loads can cause certain materials to strain or even break. When you're considering which material to use for your part, make sure you've accounted for stress load. If your part will be exposed to high stress, the material it's made of will need the elements necessary to resist loads and prevent deformation.

Dimensional Tolerance

When you're considering CNC machined components, it's important to pay close attention to dimensional tolerance. It may become an automated part of the process to go with what's been done before, but don’t underestimate the importance of dimensional tolerance . In addition to having an impact on how well your entire process works, it also has an impact on your bottom line. In addition to playing a role in selecting CNC machining materials, it also has an effect on the parts and assemblies, cutting method and what types of tools and machines will be used.

You need to know the tolerance required for your part. If you're working from an old part design or sketch and are going with what's been done in the past, it's a good idea to double check the tolerance is appropriate. Typos can easily occur in documentation. Even if the information is correct, if an adjustment can be made to loosen the tolerance and still allow the part to work to its full potential, you could save money by re-evaluating tolerance. Tighter tolerances are often more expensive to produce.

There is a standard dimensional tolerance that is used as a default, but if you don't specify a tolerance, or discover that your numbers are off, you’ll end up ordering a part that may not fit. Needless to say, your new part won't work like new, rather it may not work at all. While you can fix this, it will take more time out of your project to have it resized and/or reordered, and will end up costing you more than if you had determined the necessary tolerance up front. This simple initial step can help you save money in the long run.

If you aren't sure what the exact tolerance is for the part you need, don't make an educated guess, instead, let a CNC machining company like American Micro Industries help you figure it out.

Type of Fastening Required

steel fasteners

If the CNC machined components you need are going to be used as fasteners, it's important to consider that as you choose a material. The material will have an effect on how securely fasteners will fit together. Different materials have different properties — for example strength, corrosion resistance, brittleness and galvanic corrosion — and so you should choose a material that reflects the properties you want your fasteners to have. The most common material for fasteners is steel , but that doesn't mean it's safe to assume that steel is the best fit for your fastener.

If you're searching for a new part to fasten, it needs to fit perfectly. If you fail to consider the type of fastening when you're deciding on a material, your mechanism may not function properly.

What Are the Operating Temperatures?

It's important to consider the operating temperature the part will need to withstand when it's in place as a part of your process. You want to be sure the melting point of the material you choose is lower than that of the operating temperature. You also want to be sure if there are fluctuations in operating temperature that the material you choose can handle it. While some of the more durable materials are built to withstand these changes, many will show signs of warping, expansion and/or break-down over time. Extreme temperatures can also negatively impact the durability of some materials.

This information is equally as important to know when you're CNC machining materials, so you can be sure the temperatures that result from the cutting and shaping of the part will not distort it. Making that connection between the operating temperature and the material you’re using is essential to a successful design and production run.

High Temperatures and Their Impact on Materials

High temperatures play a crucial role when selecting what materials to use, as many will deteriorate under extreme heat. A popular plastic that doesn’t hold up well under extremely high temperatures is polyvinyl chloride, or PVC. While it has a good fire resistance rating, its working temperature is about 176° F. Stability tends to be lost around 280° F, making it unfit for some projects.

There are some materials that are built to be resilient and durable under these high-heat conditions. For example, polyisocyanurate has properties that do not allow it to melt or freeze. The thermoset plastic is processed as a viscous material first, allowing it to form multiple shapes. After curing, it becomes rigid and exceptionally stable. When you're wondering what materials can be used in a CNC machine to create the part you need, make sure you consider how the material handles high temperatures.

Weight and Stress Capacity as a Function of Designing

Depending on what you want to do with your CNC machined components, you should consider the weight of your materials. Bigger isn’t always better, and less doesn’t always mean more — especially when it comes down to cost.

1. Heavy Materials

Heavy materials absorb a great deal of stress. For projects that require excessive weight bearing capabilities and resistance to high stress loads, heavy materials are something to consider. If you work on weight-sensitive projects, however, a heavy material isn't going to be your best option.

2. Lightweight Materials

lightweight materials

Lightweight materials are popular for weight-sensitive projects. While they are not as hefty as heavy materials, they still are durable and able to absorb a substantial amount of stress. Unfortunately, they are not very cost-effective, as they usually won’t include every option desired for your project. Lightweight materials are ideal for a good number of products, but if cost is an important factor, they might not be a good fit.

Choosing between heavy and lightweight materials is just one example of what it's important to prioritize what characteristics are most important for your CNC machined part. That way, you can specify what elements are crucial for your part in order for it function properly, eliminate materials that don’t meet those standards and then compare costs.

What Strength Profile Is Required?

Strength doesn’t necessarily mean how much weight an object can withstand. There are more components that may need to be examined, such as:

  • Tensile Strength: An object’s resistance to breaking under tension.
  • Endurance Strength: Overall capacity for stress absorption.
  • Wear Resistance: The ability for an object to handle friction or have self-lubricating characteristics. A good example of this is Ultra High Molecular Weight Polyethylene, or UHMW. It’s a similar product to Teflon®, but it is more abrasion resistant.
  • Hardness: The ability of an object to withstand pinpoint surface loads. This is usually indicated with a Brinell or Rockwell hardness number.

Overall Project Cost and Material Manufacturability

The most expensive materials are usually high-strength, lightweight materials. The best method of choosing a cost-effective component is selecting one that meets your strength profile, temperature restrictions and fitment requirements. The more crucial requirements or restrictions you have for your materials, the easier it will be to focus on key elements needed in that component.

Finding an industry that provides free quotes and no minimum for your materials will help cut costs right off the bat. Once you narrow down all that, you can have a more cost-efficient material that meets the majority of your needs.

What Materials Can Be Used in a CNC Machine?


A better question might actually be what materials can’t be used. CNC machines cut through nearly any material you can think of. While there are a wide-range of materials you can use in a CNC machine, the most commonly employed materials used are:

  • Metals — such as aluminum, brass or steel.
  • Plastics — numerous choices such as Acetal (POM), Acrylics (PMMA), Polycarbonate (PC) and Polypropylene (PP), just to name a few.
  • Wood — usually less to choose from but commonly hardwood, plywood, softwood etc.
  • Foam — tend to be more lightweight yet durable. The two main types are carving foam and rigid foam.

What Type of Material Should You Try?

rigid foam

Once you've considered all of the factors listed above, chances are you'll be able to determine which material is the best fit for your part. It may take some level of tweaking and experimenting to find the exact choice. Here’s an overview of four popular materials used in CNC machined components:

  • Rigid foam : By methods of conduction, this material serves as the foam with the highest insulation value. That said, it can perform in temperatures as low as -100° F and as high as 200° F. It also holds a higher R-value , which makes it a premium choice for floors, walls and other structure-based products that need to withstand moisture.
  • Carving foam : This material can take on nearly any shape. It’s usually used as a model for molds because of its flexibility but it's also used in components such as gaskets and seals. Carving foam contains polyisocyanurate, which is dense and resistant to extreme temperatures.
  • Phenolics : If you need to meet military-grade specifications such as MIL-I-24768, phenolics can meet this requirement. There are several to choose from — CE, LE, G10, G10/FR4, G9, G11 and G7 to give a few examples. Each has its own set of strengths. For example, the fine weave phenolic linen yields good mechanical properties, dimensional stability and a better finish for machined components than the CE material. However, it’s not suggested for electrical primary insulation. LE phenolics will meet Mil-I-24768/13 FBE requirements, while CE meets Mil-I-24768/14 FBG requirements.
  • Plastics : There are many types of plastics, a majority are used for bushings, bearings or electrical insulation. That said, a market exists for the more popular types of plastics. The range of uses are broad and benefits many industries, such as aerospace, automotive, medical and electronics.

General Tips on CNC Machining Certain Materials

The decision of which of the CNC machining materials to use for your part ultimate depends on what you’re looking to create, but here are some general tips to use as a brief CNC machining materials guide.

  • Don't assume metals are your best option. Non-metallic materials have become popular because they are lightweight yet durable — like foam you can mold into various different shapes. Non-metals also retain small details during cutting. If your project seems like one that may benefit from the use of non-metals, there are plenty of options that can benefit your final product.
  • Remember that rigid foam and carving foam serve different purposes. While both are lightweight yet durable, rigid foam is best for parts with a focus on structural integrity and stability, while carving foam is often used as insulation and prototypes for molds.
  • Phenolics are great options. Especially when you need to adhere to specific regulations or specifications for military-related projects.
  • There are a wide variety of diverse plastics available. Acetal is often used for bushing and bearing replacements. Polyvinylidene fluoride polymer, or PVDF, is used in insulation for electrical wiring. Then you have plastics like UHMW. You can employ UHMW in medical biomaterial, such as knee, hip and spine replacement devices. These are just a few examples of the endless possibilities offered by plastics.

Contact American Micro Industries to Discuss CNC Machining for Your Materials

Ask yourself what type of company you want to work with to machine your materials. Look for turn-key industries with strong attention to detail and ability to create hard-to-find parts. Do your research and select your company based on values, quality and efficiency as well. American Micro Industries offers the solutions you need in a timely and affordable fashion.

This guide should provide some insight and guidance to your decision-making process. Get in touch with us to discuss any additional concerns about materials or the machining process. This can help clear up any lingering questions you may have. When you are ready to begin, we are ready to assist you.