If you’ve ever sent a design file to a CNC milling service and waited for a part that fit your exact specs, you probably didn’t think much about the raw material that would go into the machine. But as someone who runs a CNC milling service that’s handled everything from tiny aerospace brackets to large consumer electronics housings, I’ll tell you this: choosing the right material is half the battle. Pick the wrong one, and even the most precise milling job will end up warping, corroding, or failing just when you need it most. Over the 12 years I’ve been in this business, I’ve seen too many projects derailed by a material misstep—so today, I’m breaking down the most common, most reliable materials we use for CNC milling, along with what makes each one work (or not work) for different jobs. CNC Milling Service
Let’s start with metals, because that’s the bread and butter of most CNC milling work. Metals are valued for their strength, durability, and ability to hold tight tolerances, and we mill with a huge range of them. The first group that comes up in nearly every conversation is aluminum. It’s lightweight, corrosion-resistant, and way easier to mill than steel, which makes it a go-to for everything from drone parts to phone cases. For example, a few months back, we worked with a startup that makes portable power banks; they needed aluminum frames that were thin enough to slide into a pocket but stiff enough to protect the battery from drops. We used 6061 aluminum for that job—it has a perfect balance of machinability and strength, and it takes a nice smooth finish after milling. If they’d picked a harder aluminum, like 7075, it would have taken twice as long to mill and cost more, and if they’d gone too soft, it would have bent if someone sat on their power bank in a backpack.
Steel is another big one, though it’s trickier to mill. Carbon steel is super strong and affordable, so we use it for heavy-duty parts like bolts, gears, and agricultural equipment components. But it’s prone to rust, so if a part is going to be exposed to moisture, we recommend adding a coating afterward—like powder coating or zinc plating. Stainless steel, on the other hand, is corrosion-resistant, which makes it ideal for medical devices, food processing equipment, and marine parts. The most common stainless steel we mill is 304, which is easy to work with and doesn’t break milling tools as much as the harder 316 grade. That said, 316 is non-reactive enough to use in surgical instruments, so it’s worth the extra milling time for those jobs. We recently finished a run of 500 surgical scalpel handles for a local medical device company, and every single one met their 0.001-inch tolerance requirement—all because we picked 316 stainless and adjusted our milling feeds and speeds to account for its toughness.
Then there are specialty metals, which we use for more niche, high-stakes projects. Titanium is a big one in aerospace and automotive racing; it’s way stronger than aluminum but lighter than steel, and it can handle extreme temperatures. The downside? It’s expensive and really hard on milling tools—we have to use solid carbide end mills and slow down our process a lot, so titanium parts cost more. But when a customer needs a bracket that won’t crack at 50,000 feet or withstand 200 mph on a race track, titanium is the only way to go. We also mill brass and copper for electrical components, like connectors and heat sinks. Brass is easy to machine and has good conductivity, so we use it for custom electrical terminals, and copper is perfect for heat exchangers because it transfers heat so efficiently. Just last quarter, we helped a tech company prototype a custom heat sink for a gaming PC; their original design used aluminum, but it ran too hot, so we milled a small batch from pure copper, and it cut their CPU temperature by 15 degrees under load.
Now, moving on to plastics—they’re more common than you might think, and they’re great for parts that need to be lightweight, non-conductive, or cheap for low-volume runs. Acrylic (PMMA) is probably the most popular plastic we mill; it’s clear, rigid, and affordable, so we use it for signs, display cases, and even prototype parts. The trick with acrylic is that it can melt or chip if the milling tools are too sharp, so we have to adjust our settings to get a clean edge without scratching it. For parts that need to hold up to heat, nylon is a top pick. It’s tough, flexible, and resistant to abrasion, so it’s great for gears, bushings, and even small robot parts. We mill nylon all the time for hobbyists and small engineering teams, and it’s way more forgiving than metal—we can knock out a prototype part in an hour without worrying too much about tool wear, which saves customers time and money.
We also mill polycarbonate, which is similar to acrylic but way more impact-resistant—you can drop a polycarbonate part and it won’t shatter, which makes it ideal for safety goggles, machine guards, and drone housings. And for parts that need to be non-conductive for electronics, we use acetal (also called Delrin). It’s rigid, has a low friction coefficient, so it’s perfect for bearings and sliding parts. Last year, we worked with a robotics company that needed a custom gear for their warehouse robot’s arm; they tried 3D printing a nylon gear, but it wore out after a month, so we milled it from acetal, and it’s still running six months later with no visible wear.
Beyond metals and plastics, there are a few composite materials that have exploded in popularity for CNC milling over the last decade. Composites are made from two or more different materials, so they combine the best properties of each—like strength and light weight. Carbon fiber reinforced polymer (CFRP) is the most common composite we mill; it’s super strong, lighter than aluminum, and doesn’t conduct electricity, which makes it great for aerospace parts, racing car bodies, and custom bicycle frames. But milling carbon fiber is tricky—its fibers can fray if tools aren’t sharp, so we use diamond-coated end mills to get clean, smooth edges. We also mill fiberglass, which is similar to CFRP but less strong, and it’s used for things like boat parts and electrical insulators. Another composite we work with is G10, a fiberglass-epoxy laminate that’s super rigid and heat-resistant; it’s often used for knife handles, electrical circuit boards, and custom tooling. I’ve milled hundreds of G10 parts over the years, and it’s one of my favorite materials to work with—you can get such a precise, clean finish, and it’s way more durable than plastic for custom parts.
Of course, no material is perfect, and part of our job as a CNC milling service is helping customers pick the right one for their specific needs. We don’t just say “aluminum works” or “plastic works”—we ask questions: What’s this part going to be used for? Does it need to withstand heat, corrosion, or heavy loads? What’s your budget? How many parts do you need? For example, a customer might come to us with a prototype part that’s supposed to be a small bracket, and they think aluminum is the only way. But if they’re only making 10 parts for a proof of concept, and the bracket doesn’t need to hold more than a few pounds, we might suggest acetal plastic instead—it’s cheaper, faster to mill, and lighter, which is better for a prototype. On the other hand, if they’re making 10,000 brackets that need to hold 50 pounds each and last for years, we’ll steer them toward 6061 aluminum, which is strong and cost-effective for high volume.
I also want to mention a few things that trip customers up all the time. First, machinability is a big factor—some materials look similar on paper, but milling them is totally different. 6061 aluminum is easy, but a 6061-T6 temper is harder and takes longer to mill, so that’s a cost difference right there. And when it comes to plastics, acrylic is cheap and easy, but it can warp if you mill too fast because the heat from the tool melts it. We’ve had to remill parts for customers who didn’t know that, so we always give them a heads up on setting expectations. Another common mistake is picking a material that’s too heavy. A lot of aerospace and drone projects are focused on reducing weight, so choosing a steel part instead of aluminum would add unnecessary pounds and hurt their performance.
At the end of the day, the best material for your CNC milled part isn’t just the strongest or the cheapest—it’s the one that checks all your boxes: performance, cost, lead time, and durability. As a CNC milling service, we’ve got the experience to walk you through all these options, answer your questions, and make sure you don’t waste money on the wrong material. Whether you’re a startup prototyping a new gadget, a small business needing custom parts for your equipment, or a larger company with a high-volume project, we can work with you to pick the perfect material, mill it to your exact tolerances, and deliver parts that work as well as you designed them.
If you’re working on a new project and aren’t sure what material is right for your CNC milled parts, we’d love to chat. We’ve helped hundreds of customers sort through material options, fix design issues, and get parts that fit their needs perfectly. Reach out to our team to discuss your project details, and we’ll provide a free quote and guidance tailored to your specific needs.
Precision Machining References
ASM International. (2006). Materials Park: Aluminum Alloys.
Klocke, F., et al. (2015). Machining of Carbon Fiber Reinforced Polymers – A Review. CIRP Annals – Manufacturing Technology.
plasticsToday. (2022). Engineering Plastics for CNC Milling.
ASTM International. (2018). Standard Specification for Stainless Steel Bars and Shapes.
Ningbo Yirui Machinery Manufacturing Co., Ltd.
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