Reduced manufacturing costs are frequently the primary objective in CNC processing, whether you want to build a single prototype or prepare for mass production. Fortunately, as a designer, your selection will have a significant impact on the final cost. You may produce optimized components while minimizing costs and meeting design criteria by using the “Design for Machinability” approach described in this article.

What factors influence the price of CNC parts?

The cost of CNC machined parts is determined by the following factors:
Processing time: The longer it takes to process parts, the higher the price. The biggest cost driver in CNC is often processing time.

Start-up expenses are substantial for small-batch manufacturing since they are tied to CAD file preparation and process design. This cost is constant, however, there is a chance to lower the unit price by utilizing “economies of scale.”

Material cost: the cost of materials and the complexity of processing materials have a significant influence on total cost. By optimizing the design while taking some material concerns into account, the price may be considerably decreased.
Other manufacturing expenses: When designing parts with unique criteria (for example, when defining rigorous tolerances or designing thin walls), additional tools, stricter quality control, and more processing steps may be required (at a lower processing speed). Naturally, this will have an effect on the whole production time (and price).

Now that we know where the CNC cost is coming from, let’s look at how we can optimize the design to reduce it.

13 Strategies For Reducing The Cost Of CNC Components

Tip 1: Give the inner vertical edge a radius.
When cutting the cavity’s edge, all CNC milling tools have a cylindrical form and generate a radius.

A tool with a smaller diameter can be used to lower the corner radius. This implies that several tool paths must be performed at a slower speed – smaller tools cannot remove materials in a single tool path as rapidly as large tools – increasing processing time and expense. Add a radius equal to at least one-third of the cavity depth (the larger the better).

The same radius should be used on all interior edges.

At the cavity’s bottom, specify a tiny radius (0.5 or 1 mm) or no radius at all.

The corner radius should ideally be somewhat more than the tool radius used to manufacture the cavity. This reduces the stress on the tool and hence lowers production costs. For example, if your design includes a 12 mm deep cavity, give the corner a 5 mm (or bigger) radius. This allows the 8mm tool (with a radius of 4mm) to cut them more quickly.

Tip 2: Keep the cavity depth to a minimum.
Instead of lowering the radius of the inner edge, use a form with undercuts if you require an inner edge with sharp corners (for example, when a rectangular item needs to fit into a hollow).

Machining deep holes increase the cost of CNC components because a considerable quantity of material must be removed, which takes a long time.

Remember that CNC tools have restricted cutting lengths: in general, they perform best when the cutting depth approaches 2-3 times their diameter. A 12 milling cutter, for example, may securely cut holes up to 25 mm deep.

Deeper cavities can be cut (up to four times or more the diameter of the tool), however, this raises expenses due to the requirement for special tools or multi-axis CNC systems.

Furthermore, the tool must be angled to the correct cutting depth when cutting the cavity. Enough room is required for a smooth entry.

Reduce costs by limiting the depth of any cavities to four times their length (i.e. the maximum dimension on the XY plane).

Tip 3: Make the narrow wall thicker.
Unless weight is the most important consideration, thick solid portions are more stable (have a cheaper manufacturing cost) and should be favored.

When machining thin walls, several tool paths at low cutting depths are required to minimize distortion or breakage. Because thin features are prone to vibration, precisely machining them is difficult and can greatly increase processing time.

Reduce costs: For metal parts, the design wall thickness should be more than 0.8mm (the thicker, the better).

The minimum wall thickness for plastic items must be more than 1.5mm.

Metal has a minimum wall thickness of 0.5 mm while plastic has a minimum wall thickness of 1.0 mm. However, the machinability of these traits must be assessed on an individual basis.

Tip 4: Keep the thread length to a minimum.
Because extra equipment may be needed, selecting threads that are longer than necessary may raise the cost of CNC components.

Keep in mind that threads that are longer than 0.5 times the diameter of the hole do not enhance the connection strength.

Reduce costs by designing threads that are no longer than three times the diameter of the hole.

When threading blind holes, provide at least 1/2 diameter unthreaded length at the bottom of the hole.

Tip 5: Create standard-sized holes.
The conventional drill bit may be used with CNC to make holes fast and precisely. End mills must be used to machine holes with non-standard dimensions, which may raise expenses.

Furthermore, limit the depth of all holes to four times their diameter. Deeper holes (up to ten times the diameter) can be drilled, although they may be more expensive to process.

Reduce costs by increasing the diameter of the designed hole by 0.1 mm for holes with a diameter of 10 mm or less and greater than 0.5 mm.

Please utilize the typical inch fraction or refer to the fractional inch drill size chart when designing in inches.

Design length up to four times the diameter of the hole.

Tip 6: Only define severe limits when absolutely required.
Strict tolerances raise the cost of CNC because they increase production time and need a manual inspection. Tolerances should only be properly defined when absolutely necessary.

If no specific tolerance is specified on the technical design, the item will be machined with standard tolerance ( 0.125 mm or greater), which is enough for the majority of noncritical features.

Internal feature tolerances are very challenging to obtain. When cutting cross holes or cavities, for example, tiny flaws (called burrs) may emerge at the margins owing to material deformation. Parts having such characteristics must be examined and deburred, which are both manual (and time-consuming), raising costs.

Reduce costs by specifying finer tolerances only when absolutely essential.

As a reference for all toleranced dimensions, define a single datum (such as a cross section of two edges).

Because they usually define loose tolerances, the use of geometric dimensioning and tolerance dimensioning (GD&T) in technical drawings (such as flatness, straightness, roundness, and real position) can reduce the cost of NC processing, but they require advanced design knowledge to be effectively applied.

Tip 7: Limit the amount of machine settings.
Because it is normally done by hand, rotating or repositioning an item raises production costs. Furthermore, for complicated geometry, specialized fixtures may be necessary, which raises prices even further. Particularly intricate geometries may necessitate multi-axis CNC equipment, raising expenses even more.

Consider dividing the pieces into geometric forms that can be produced by CNC in a single setting and then joining them with bolts or welding. This is also true for pieces with extremely deep voids.

Reduce costs by designing pieces that can only be machined in a single setting.

Please break the geometry into components for subsequent assembly if this is not possible.

Tip 8: Stay away from tiny features with a high aspect ratio.
Small features with a high width to aspect ratio are prone to vibration, making precise processing difficult.

They should be joined to thicker walls or strengthened with support ribs to increase rigidity (preferably four: one on each side).

Reduce costs by designing elements with an aspect ratio of less than 4. To increase the rigidity of the walls, add bracing or attach minor features.

Tip 9: Remove any text and writing.
Because extra and time-consuming processing procedures are necessary, adding text to the surfaces of CNC-machined objects can dramatically raise prices.

Surface finishing techniques such as silk screen printing or painting are less expensive ways to add text to the surface of CNC machined items.

Reduce costs by removing all words and letters from CNC machined items.

If you need words, you should carve them rather than emboss them because the latter requires more material to be removed.

Tip 10: Consider material machinability.
The ease with which materials may be cut is referred to as machinability. The greater the machinability, the faster the CNC can process materials, lowering costs.

Each material’s machinability is determined by its physical qualities. In general, the simpler it is to mill a metal alloy, the softer (and more ductile) it is.

Reduce costs: If you have the option, use materials that are easier to machine (especially for large batch orders).

Tip 11: Consider the cost of bulk supplies.
Another element that can significantly impact the price of CNC machined components is the cost of materials.

Aluminum 6061 is clearly the most cost-effective material for producing metal prototypes, since it combines cheap cost with excellent processability.

Reduce costs by selecting materials with low batch costs (especially small batch orders).

Tip 12: Avoid (many) surface treatments.
Surface treatment enhances the look and resistance of CNC machined items to severe environments, but it also raises their price.

Multiple surface treatments on the same part will raise the price even more since extra procedures are necessary.

Reduce costs by selecting the surface finish after machining.

Only when absolutely essential do several surface treatments become necessary.

Tip 13: Consider the blank size.
The entire cost may be affected by the size of the blank. Some materials must be removed from all corners of the component to ensure precision. This will have a substantial influence on material costs (especially for large orders). As a general guideline, the blank should be at least 3 mm bigger than the end.

Reduce costs by designing parts that are 3 mm smaller than the conventional blank size.

For reference, use a standard blank size chart or a major material supplier catalog.