The Secret of CNC Prototyping, A Cost Breakdown

Leon Huang: Rapid Direct Author

The Secret of CNC Prototyping, A Cost Breakdown

Whether we like to admit it or not, one of the most important factors in choosing a CNC prototyping service is cost. And though finding the right balance between low cost and high quality is crucial, it is sometimes difficult to navigate. For instance, some clients may be wary of choosing a rapid prototyping service whose quotes seem too low. Fortunately, there is a way around feeling overwhelmed when choosing a CNC prototyping partner. It all comes down to understanding where the costs of CNC machining come from.

In the following article, we’ll break down the costs associated with CNC prototyping, showing you exactly where cost matters and where costs can be reduced. A skilled manufacturing service such as RapidDirect understands the ins and outs of CNC prototyping and can therefore deliver high quality parts at competitive costs.

The real cost of CNC machining

There is an abundance of information online about how much CNC prototyping costs and much of it feels contradictory. While some claim it as the most cost-efficient prototyping process, some say it is the least. Believe us, we know how confusing it can get. That’s why we’re not here to make those claims: we are here to look at how much CNC machining costs for prototyping and where those costs come from.

The first thing to realize is that the cost of CNC prototyping can vary widely, depending on what material you are working with, what tolerances your part requires and how complex the part design is. By understanding each cost driver for CNC prototyping as well as other cost influencers you can determine how much you should be paying and what a competitive CNC-based prototyping service should cost.

CNC prototyping cost drivers

There are several factors that are cost drivers for CNC prototyping. The most important ones are the following:

1. Design complexity

cnc prototyping design

One of the factors that affects the cost of CNC machining the most is part design. If your prototype has a straightforward design, with simple geometry, then it will be significantly cheaper than one with a more complex structure. This is based on the simple fact that a simple geometry is faster to machine than a complex one.

For example, if your prototype design integrates undercuts, many hole sizes and a high level of detail, the machining time will be longer than a part that requires minimal cuts and milling. If cost is a key concern for your project, consider taking a look over your design and evaluating whether certain design elements are necessary and if it can be simplified to reduce machining time. Our design experts at RapidDirect can also offer support to optimize your part design.

2. Tolerances

cnc prototyping tolerance
engineering tools on technical drawing

Another key cost driver for CNC prototyping is tolerances. In other words: how precise your product or prototype must be. CNC machining is one of the most high-precision manufacturing processes that exists today. But that doesn’t necessarily mean your part always requires the highest degree of precision. The tighter the part tolerances, the more costly the CNC machining process becomes, because of the added time it takes to achieve high levels of precision.

According to a study by the University of Illinois, the cost of CNC machining can increase by double between a rough tolerance of ±0.030 and a standard tolerance of ±0.005. Looking at tolerances of ±0.001? The cost can increase by up to four times. Considering this, do not be alarmed if you receive a shocking quote if you’ve asked for the tightest tolerances possible. Chances are, if you are ordering a prototype, it may not need the highest tolerances, which will enable you to scale back the costs of production.

3. Material choice

cnc prototyping materials

This should go without saying, but the choice of material will impact the overall cost of CNC prototyping. The cost of the raw material is often out of the hands of the CNC machining service, however different global regions have different costs. For instance, rapid prototyping services in China often have access to cheaper raw materials, which is why they can often offer lower production costs.

As a general rule, plastic materials are cheaper than metal. But that doesn’t narrow down very much, as there are many plastic and metals to choose from. For prototyping, plastics are often the most common option due to cost. Among CNC prototyping plastics, ABS is one of the most cost effective. POM, PC, PA and PMMA are also common. Looking at metals, aluminum alloys are usually the most cost effective, which makes them popular for prototyping applications. You can see RapidDirect’s full list of CNC machining materials here.

It is also worth noting that it is not only the cost of the raw material that influences cost: the machinability of the material also has an impact because less machinable materials take more time to process, which drives up cost.

4. Finishing choice

CNC prototyping surface finishing

The fourth major cost driver for CNC prototyping is finishing. There are several post-processing options and each has a different price tag. Fortunately, there is also the option for no post-processing (aka “as-machined” or “as-milled”), which is viable for prototyping applications on a strict budget.

Finishing processes impart different characteristics for your prototype or final part, including aesthetic qualities like smoothness or gloss, and functional properties like better durability. If a surface treatment is needed for your CNC prototype, minimize the cost by choosing one, rather than multiple finishes.

CNC Prototyping Cost Influencers

In addition to the four aforementioned cost drivers, there are a handful of factors that influence the cost of CNC prototyping, though in less direct ways. These influencers also vary from service to service, so it may be worth discussing with your prototyping partner to understand their specific pricing model.

  1. Type of CNC machining
type of cnc machining

Though this is a topic for another blog article, there are many variations of CNC machining, some of which are more advanced or more costly than others. For instance, there are 3-axis and multi-axis CNC machines, as well as milling and turning machines. Each of these falls somewhere different on the price spectrum. For example, a 3-axis CNC turning machine is typically cheaper to operate than a 3-axis milling machine. Multi-axis machines, which are capable of more complex geometries, cost more to run.

Typically, CNC prototyping services will offer many CNC machining options. At RapidDirect, we offer 200 sets of 3, 4 and 5-axis CNC machines, as well as a wide range of auxiliary equipment. If you aren’t sure which CNC machine is the right choice for your prototype, don’t hesitate to reach out. We can help you choose the right machine for your application and budget.

2. Order size

cnc machining order qty

This one may seem obvious: the more parts you order the more you will pay. But it’s actually more complex since the economy of scale comes into play. This means that the cost of ordering one part may not necessarily increase relative to how many parts you order. Rather, the larger the volume of parts, the cheaper the cost per part will become.

The economies of scale are not just applicable to injection molding, where the high cost of tooling is absorbed the more parts are made. It also comes into play for CNC prototyping. This is largely because once a service has done the work to prepare and manufacture a part, the process can be replicated without the same degree of preparation each time. It may not influence material costs, but it can reduce costs associated with labor and time.

3. Labor

cnc machining labor

Last but not least is the question of labor. The cost of CNC machining is not only made up of material and machine costs: CNC machining providers also have to pay a highly skilled team of operators, as well as design engineers and other support staff. The cost of labor is therefore built into the quote you receive from your CNC service.

The cost of labor is, however, directly tied to many other elements mentioned in this article. For instance, a prototype with a complex geometry that will take longer to manufacture will require more labor. This leads to a higher cost than a simple part that requires less time to machine and thus less labor. Labor costs are also driven before the manufacturing stage. If your design requires digitization or optimization for production, the costs of a design engineer will be factored into your production costs.

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