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Calculating the Cost of CNC Machining Custom Parts

CNC machining is the most common technology for creating complex parts out of both metal and engineering plastics. When deciding to machine a part this way, the first questions that often come up are, “How much will it cost?” and “What can be done to reduce the overall cost?” This article will break down all the common cost factors that come into play when CNC machining a part and help elucidate how CNC machining cost estimates are determined.

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1. Material

The material used to create a part is often a driving factor behind the cost. Obviously, the raw material costs money, but that’s not the end of its story. The specific material also dictates what type of tooling you’ll need and the speed at which those tools can run. Both of these factors can have sizable effects on part cost. The overall cost of unnecessarily choosing an expensive superalloy can quickly compound due to specialized tooling requirements.

2. Part Complexity

It is important to follow general DFM (Design for manufacturing) principles when designing parts for CNC machining. Complex shapes and difficult-to-machine features can cause the cost to CNC a part to skyrocket. This is because complex parts may need multiple setups to machine all the features. Each time the part is set up the operators’ cost and the machine downtime must be accounted for. For highly complex parts, 5-axis machines may be needed, and running these machines is more expensive than running 3-axis machines in terms of the skills needed to operate them and the higher upfront cost of the machine itself. Although, the cost is also lesser due to the reduced downtime of processing with a 5-axis machine. In addition to this, the cost of programming the part needs to be taken into account; more complex parts require additional programming hours. 

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CNC Machining Industry
CNC Machining Industry
CNC Machining Industry

Complex machining is required for aircraft engines

3. Tolerancing

Modern CNC machines are capable of reaching incredible accuracy and repeatability. However, specifying extreme tolerances for every feature, be it critical or noncritical, can significantly increase the cost to CNC a part. This is because different tooling setups may be required and machine times need to be extended to achieve high accuracy. Only specify tight tolerances on critical features. On top of the machining time, each toleranced feature will need to be inspected, adding additional labor time.

FREE CNC Machining Design Guide

4. Surface Finish

CNC machined parts often have visible machining lines that get created while material is getting removed, but which do not affect the dimensional accuracy of the part. In most cases, the surface can be left as is. However, a mirror-like finish is sometimes requested for aesthetic reasons. Specifying such finishes across all surfaces can impact the final cost to CNC machine a part. More often than not, the part will need to be moved to grinding & polishing machines to achieve especially tight surface requirements. If surface finishing is done on a CNC machine, specialized tooling and longer machining times are required which will further increase the cost.  

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CNC machine at work
CNC machine at work
CNC machine at work

Tight tolerances can increase cost

5. Part Quantity

The total quantity of the parts required will also affect the overall cost to CNC a part. Manufacturing a one-off part will always be more expensive per unit when compared to doing multiples of the same design. This is because the part only needs to be programmed once. Plus, bulk material orders can include discounts, multiple parts can be set up at once, and the cost of designing the fixturing is also shared between all the parts. The higher the volume, the lower the unit cost will be.

Calculating the Cost of a CNC Part

Calculating the cost to CNC a part is a combination of all the above-mentioned factors. The weighting of these factors also varies with each application, so there’s no satisfactory rule of thumb for calculating the cost to CNC machine a part. However, Xometry offers free and instant online quotes on CNC machined parts that will give you a free cost estimate via the Xometry Instant Quoting Engine. This feature-based cost estimation allows for an accurate estimate for any part and takes all the guesswork out of the process. Each of the parameters can be tweaked so that their individual effects on cost can be determined and optimized. Visit Xometry’s website for your part cost-estimation needs!