A bunch of gears on a table

Custom Manufacturing: Choosing the Right Material for Your Products

Selecting the right material for any product is important. However, material selection can be daunting because there are so many available choices. Additionally, no one-size-fits-all material option exists because each product/application and customer has different requirements. Having a basic understanding of the available material options can simplify your decision-making process. 

Below, we’ll discuss some of the most common materials available, including their advantages and disadvantages.


Different types of stainless steel tubes and profiles

Steel combines iron (generally more than 98%) with small amounts of carbon and other elements. Adding different elements creates different grades of steel. Most steel grades are relatively inexpensive, readily available, easily machinable, and incredibly durable. Broadly, there are four categories of steel: low-carbon, medium-carbon, high-carbon, and stainless.

Low-Carbon Steel

Low-carbon steel alloys, such as grades A36 and 1018, contain between 0.05 and 0.29% carbon. They’re often referred to as “mild” steel and are very ductile, meaning they can be easily machined, molded, drawn, and otherwise worked into final products. Because they’re relatively easy to work with, they are less expensive to machine than higher-carbon alloys. 

Low-carbon alloys can be machined faster, result in less tool wear, and are less prone to work-hardening. However, that ease of work comes with very low resistance to corrosion and lower hardness and durability than their higher-carbon counterparts.

Low-carbon alloys are also less easy to harden because they lack the carbon necessary to harden on their own. However,  this steel type can be hardened through processes such as case hardening and carburization. 

Medium-Carbon Steel

Medium-carbon steel alloys, like grades 1045 and 4140, contain between 0.30 and 0.60% carbon and between 0.60 and 1.65% manganese. This steel type is less ductile than mild steel but has greater tensile strength and hardness. This combination significantly increases the final product’s durability.

Medium-carbon steels are the ‘workhorse’ of steel and can be found in products ranging from pistons and crankshafts to pulleys and sheaves. They are more difficult to machine but not overwhelmingly so, and they can be readily hardened to 60 to 65 HRC, making it incredibly durable for applications, such as gears, where you have continuous metal-on-metal contact. This steel type is also less susceptible to corrosion. 

High-Carbon Steel

High-carbon steel alloys, like grades 1080 and A-2, contain between 0.60 and 1.00% carbon and 0.30 and 0.90% manganese. This steel type is then alloyed with other elements, such as tungsten, vanadium, and molybdenum, which increases its resistance to tempering from heat generated during its use. The result is an alloy that is far less ductile than either low- or medium-carbon steel but is generally incredibly hard and strong and perfectly suited to make products like knives, hobs, and end mills. 

High-carbon steel can also be alloyed with silicon to enhance its flexibility. However, this quality makes it expensive, difficult to machine, and brittle, so it should only be used in the appropriate applications, like automotive suspension components.

Stainless Steel

Stainless steel alloys contain carbon amounts ranging from 0.03 to 0.10%, with the most common grades containing about 0.08%. This composition technically makes those grades high-carbon steel, but their real defining feature is the addition of significant amounts of chromium (16 to 18%) and nickel (8 to 14%), which greatly increases their resistance to corrosion. 

These alloys are used in the food processing, medical, marine, and automotive industries and anywhere else where high strength and good corrosion resistance are required. 

The most common stainless steel grade is 304, which is decently machinable and ductile, and has good corrosion resistance and tensile strength. The second most common grade is 316, which is similar to 304, but has 2 to 3% molybdenum added to it. That additional molybdenum provides excellent resistance to corrosion from seawater, as well as chemicals and acids commonly used in industrial washdown environments. However, the added molybdenum increases its cost and makes the steel slightly more difficult to machine.


a 3D rendering of aluminum gears

Aluminum is an element like iron, but it will always be an aluminum alloy when used in manufacturing. Depending on the series, aluminum can be combined with varying amounts of copper, manganese, silicon, magnesium, and zinc.

In general, aluminum alloys are valued for their ease of machinability and formability, lighter weight (approximately one-third of the weight of steel), decent corrosion resistance, and good strength-to-weight ratio. Each series has its distinct uses and characteristics, which are described below.

1000 Series

1000 series alloys are at least 99% pure aluminum. They have excellent electrical and thermal conductivity and are often found in electrical lines and heat sinks.

2000 Series

2000 series incorporate copper as the secondary element, which makes them stronger than their 1000 series counterparts. They also have better machinability and can be heat-treated. These alloys are commonly found in military and aerospace applications.

3000 Series

3000 series alloys use manganese as their secondary element, which makes them more malleable, increases their corrosion resistance, improves their weldability, and makes them food-safe. However, they cannot be heat-treated. 3000 series alloys are primarily found in cookware.

4000 Series

4000 series alloys use silicon as their secondary element, giving it a lower melting point and excellent viscosity when casting, and limited shrinkage when cooling. Once cast, it is highly machinable and has good heat dissipation. This type of aluminum is commonly used to manufacture engine blocks and large cast heat sinks.

5000 Series

5000 series alloys use magnesium as their secondary element, providing better corrosion resistance and good weldability. This series is sometimes referred to as ‘marine-grade’ aluminum due to its extensive use in marine environments and applications, on bridges, and other “close to” water environments.

6000 Series

6000 series alloys use magnesium and silicon as secondary elements and are considered the ‘workhorse’ of aluminum alloys. They are reasonably strong, highly machinable, take anodizing well, and, when anodized, have exceptional corrosion resistance. They are found throughout the automotive, aerospace, and manufacturing industries.

7000 Series

7000 series alloys use zinc as their secondary element, which makes them especially strong. They are heat-treatable and have good corrosion resistance, though it takes skill to weld or form them without cracking. This series is used to manufacture aircraft landing gear and airframes, and in hydraulics applications, sports applications such as bats, arrow shafts, and bicycle frames, and any other application where a high strength-to-weight ratio is especially important.


Nuts and bolts made from Monel on a white background

Monel® is a registered trademark of the Special Metals Corporation that contains approximately one-third copper and two-thirds nickel, with smaller amounts of other elements, such as sulfur, aluminum, and titanium. It offers corrosion resistance greater than 316 stainless steel, is readily weldable and formable, and can be exceptionally strong (some alloys have more than 1300Mpa of tensile strength). 

The U.S. Navy and research vessels use Monel® for applications that are submerged in moving seawater, such as towed sonar arrays. However, it is expensive, suffers from pitting corrosion in still water, work hardens, and, if mounted to steel, galvanically corrodes.

Cast Iron

Cast iron plumbing fittings on a gray surface

Cast iron is an iron alloy that is combined with silicon to improve its castability. It is relatively inexpensive and can be used to make large gears, flywheels, or sheaves without needing to machine the entire part. It is hard and strong, though it can be brittle and corrode easily. Cast iron also requires investing in a pattern from which all future castings will be made. Cast iron is commonly found throughout the automotive and heavy industries.


Two blue bevel gears made from plastic, placed together to create a miter gear

“Plastics” covers a broad range of organic (meaning carbon-based) polymers with a range of properties that are just as wide. Some are soft and pliable at room temperature, while others, the so-called “engineering plastics,” have properties approaching those of nonferrous metals like aluminum.

Two significant advantages of plastics over metals are less weight and excellent corrosion resistance. They can also run more quietly than metals. The disadvantage is that they can lack the strength, wear resistance, and temperature range of metal components. However, they are easy to machine for small quantities and can be molded if needed in volume. Here’s a breakdown of four common plastics used to manufacture components.


Sometimes referred to as polyacetal, or more scientifically, as polyoxymethylene (POM for short), acetal is an engineering plastic. It has a semi-crystalline structure, which means it melts quickly as temperature rises rather than softening slowly as non-engineering plastics do. Other characteristics that make it attractive are its low density and friction, high strength, good chemical, wear, and impact resistance, and good dimensional stability.


Delrin™ is the trade name for the DuPont brand of acetal. Although Delrin™ is similar to other acetal plastics, there are some small differences. The main difference is that it’s considered a homopolymer, meaning the crystalline structure is uniform. This uniformity increases dimensional stability, wear resistance, and strength over what’s found in non-Delrin™ acetal materials. The machinability of Delrin™ is excellent, making it a popular choice for custom parts.


Like acetal, nylon has a semi-crystalline structure, which makes it a good candidate for many engineering applications. Nylon is about 20% stronger than Delrin™ and retains its strength at higher temperatures (up to around 210 degrees Fahrenheit), but it is also slightly water-absorbing and thus not recommended for wet or damp environments. It has a low-friction surface and is wear-resistant. Machinability is slightly inferior to that of Delrin™, but still very good. In the power transmission industry, a common variant used is glass-filled nylon, which incorporates glass powder in the nylon resin to further enhance the nylon’s strength and heat resistance.


Polyethylene isn’t generally considered an engineering plastic, but Ultra High Molecular Weight (UHMW) polyethylene is the exception. Its high density gives it good strength, although significantly lower than that of acetal. It’s also famously slippery and abrasion-resistant and has good impact absorption properties. While described as having a high molecular weight compared to metals, it’s still lightweight.

Making the Right Choice

With the wide range of materials available, how do you make the right choice? The starting point is to consider the application’s needs and challenges. You should also consider whether you want to provide lubrication and whether servicing and repair will be possible.

Working through these selection criteria will most likely eliminate some material options while opening up others. Reducing mass will push you towards aluminum or plastics, while a need for high strength is commonly answered with steel. If a custom component like a small gear is going to run dry, the low friction characteristics of plastic may be important. If corrosion is a concern, it may push you towards aluminum, stainless steel, plastics, or something more exotic, such as Monel®.

Get Help Selecting the Right Material

Using the wrong materials or not fully understanding the application requirements could result in premature wear, suboptimal performance, and, ultimately, failure.

Motion Systems has the experience and technical knowledge to help you select the right material for your custom power transmission products, including pulleys, gears, sprockets, and more. Contact us today with your questions or to discuss a specific project.