Materials for CNC Turning: Choose Wisely or Pay the Price

Picking a material for a CNC turned part seems simple enough. Find something strong enough for the job, check the price, and get machining, right?

Well, not so fast.

A material might look great on paper but be a nightmare to machine. Poor chip formation, excessive tool wear, and longer production times can turn a smart-looking choice into an expensive headache.

The cheapest raw material doesn't always make the cheapest finished part.

Choosing the right materials for CNC turning takes a little homework upfront, but your production schedule (and budget) will thank you later.

What Should You Consider When Choosing Materials for CNC Turning?

A material might check every box for your finished part, but that doesn't mean it'll play nice with a CNC lathe.

Before committing to one, there are a few things worth considering beyond how it'll perform on paper.

Machinability

Some materials are a dream to machine. Others? Well, let's just say your cutting tools won't be sending you a thank-you card.

Machinability measures how easily a material can be cut and shaped. It's often expressed as a percentage relative to a reference material, with higher ratings generally indicating easier machining.

Materials with poor machinability can create some expensive headaches:

• Faster cutting tool wear
• Longer machining times
• Poor chip formation and removal
• Difficulty achieving the desired surface finish

And those headaches add up. More time on the machine and more frequent tool replacements mean higher production costs, even if the raw material itself was relatively inexpensive.

Strength and Hardness

Tougher isn't always better.

A material needs enough strength to handle the loads it'll face, while hardness helps it resist indentation and deformation. But harder materials can also put more strain on cutting tools, making machining slower and more expensive.

The goal is to meet the part's performance requirements without paying for properties it doesn't need.

Wear and Corrosion Resistance

Wear resistance helps components withstand repeated friction and contact, while corrosion resistance protects against deterioration. The right industrial metal finishing technique can also influence how a finished component holds up.

The challenge is finding a material that can handle those conditions without creating unnecessary machining costs.

Surface Finish and Dimensional Stability

A part that looks good coming off the lathe isn't much use if it can't hold its dimensions. Some materials are easier to machine to a smooth finish, while others may deform during cutting or change dimensions with temperature. Both can cause headaches when tight tolerances are involved, so it's worth considering these properties before machining begins.

Material Cost and Availability

A lower price tag on raw material doesn't always mean a better deal. A cheaper material that takes longer to machine or wears through cutting tools faster could end up costing more in the long run.

Availability matters, too. If a particular grade is difficult to source, longer lead times and higher purchasing costs could throw a wrench into your production plans.

How Does Material Selection Affect CNC Machining Costs?

Here's where things get interesting. Two materials might get the job done, but the cost of turning them into finished parts can be wildly different.

Machining time, tool wear, and even how well a material forms chips can all affect the final price. Suddenly, that bargain-priced raw material isn't looking like such a bargain anymore.

Machining Time and Tool Wear

Every extra minute on the machine comes at a cost. Materials that are difficult to cut can slow production, wear through tooling faster, and require more frequent tool changes. Multiply that across hundreds or thousands of parts, and those extra expenses start adding up.

303 vs. 316 Stainless Steel

Not all stainless steels are created equal, especially when a CNC lathe gets involved.

According to Weber Knapp's engineers, 303 and 316 stainless steel have noticeably different machinability ratings:

• 303 Stainless Steel: Has a machinability rating of roughly 80%, making it easier to cut and less demanding on tooling.
• 316 Stainless Steel: Comes in around 40% machinability. It offers greater corrosion resistance but takes longer to machine and wears through cutting tools faster.

And there's the trade-off. If your application doesn't need the added corrosion resistance of 316, choosing 303 could save you a pretty penny in machining costs.

Acetal (Delrin) vs. Nylon

Plastics aren't off the hook, either. Take acetal (commonly known by the brand name Delrin) and nylon. Both have their place, but their machining behavior tells two different stories:

• Acetal: Cuts cleanly, produces more manageable chips, and generally machines faster.
• Nylon: Can produce long, stringy chips that tangle inside the machine, slowing production and creating headaches for machinists.

Acetal may cost more upfront, but easier machining could make it the cheaper choice when all is said and done.

When Should You Choose Plastic Over Metal?

Metal might seem like the obvious choice for a hardworking component, but don't count plastic out just yet.

Operating temperature can make a big difference in material selection. Take bushings, for example. Weber Knapp's engineers consider several options depending on how much heat the application needs to handle:

• High-temperature plastic bushings: Often the most affordable option when operating temperatures fall within the material's limits.
• Sintered bronze bushings: A step up when greater heat resistance is needed, although these can become brittle at elevated temperatures.
• Machined wrought-metal bushings: An option for higher-temperature applications where other materials won't hold up, but machining them from solid stock can increase costs and material waste.

Of course, temperature isn't the only consideration. Where the mechanism is mounted and how much heat it encounters can influence which material makes the most sense.

Sometimes, choosing the right material starts with rethinking where the part goes in the first place.

Choosing the Best Materials for CNC Turning

There's no magic material that checks every box. Even the strongest, most corrosion-resistant option can create headaches if it's difficult or expensive to machine.

The best choice comes down to balancing performance, machinability, and cost. A little thought upfront can prevent a lot of frustration once production begins. After all, the right material should work just as well on the shop floor as it does on paper.

Got a Material Question? Ask Away.

Not sure which material is the right fit for your CNC turned part? Weber Knapp's engineers can help you weigh your options before an expensive mistake makes its way into production.