Jan. 13, 2025
Construction
In computer numerical control (CNC) machining, whether you want to create a single prototype or go to large-scale production, the main priority is often reducing manufacturing costs. Fortunately, design decisions can help keep pricing down. By simply following certain Design for Machinability (DFM) rules, you can manufacture affordable parts that still comply with functional design requirements.
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This article provides extensive tips to help optimize your design. We begin by examining what drives costs up in CNC machining. We then present comprehensive guidelines, offering proven design tips to reduce the cost of your project.
A quote for CNC-machined parts is determined by the following factors:
Machining time: The longer it takes to machine a part, the more expensive it is. Machining time is often the main cost driver in CNC, especially for large-scale productions where simple design mistakes can hurt economies of scale.
Start-up costs: Related to computer-aided design (CAD) file preparation and process planning, start-up costs are significant for smaller volumes. Fortunately, they are also fixed. If the design and the surface finish are suitable for cost scaling, you can lower the unit price by applying economies of scale principles.
Other manufacturing costs: To define tight tolerances or design parts with features that are difficult to CNC machine (e.g. very thin walls), you may need special tooling, closer quality control, and more processing steps at lower machining speed. This also impacts total manufacturing time and cost.
Material cost: The price of the bulk material and the ease with which that material can be machined greatly affect the overall cost in CNC. Optimizing your design while carefully considering your material can reduce costs.
By understanding what drives the costs of CNC machining, we can optimize design to lower the budget.
All CNC milling tools have a cylindrical shape and create a radius when cutting the edge of a pocket. A corner radius can be reduced by using a tool with a smaller diameter. This requires multiple passes at lower speed because smaller tools cannot remove material as quickly as larger tools in just one pass. This increases machining time and cost.
To minimize cost:
Add a radius of at least one third of the depth of the cavity&#;the larger, the better.
Use the same radius for all internal edges to eliminate the need for tool changes.
On the floor of the cavity, use a smaller radius (.5 or 1mm) or no radius at all.
Good to know: Ideally, the corner radius should be slightly larger than the radius of the tool used to machine the cavity. This reduces the loads on the tool and thus manufacturing cost. For example, if your design has a cavity that is 12mm in depth, add a 5mm (or larger) radius at the corners. This allows a tool with an 8mm diameter to cut at a faster speed.
Pro tip: If you need internal edges with sharp corners (e.g. when a part with a rectangular shape needs to fit in the cavity), instead of reducing the internal edge&#;s radius, use a shape with undercuts like those shown in the image below.
Machining deep cavities affects the cost of CNC parts dramatically because a lot of material must be removed. This is both time-consuming and wasteful.
CNC tools have a limited cutting length. They typically work best when cutting cavities with a depth of up to two to three times their diameter. For example, a milling tool with a 12mm diameter can safely cut cavities up to 25mm in depth. It is possible to cut deeper cavities (up to four times the diameter of the tool or greater), but this drives up cost because special tooling or multi-axis CNC systems are required.
To minimize cost:
Limit the depth of all cavities to four times their length&#;that is, the largest dimension on the XY plane.
Adjust the internal corner radii accordingly. Use the advice in tip number 1 if needed.
Unless weight is a major concern, manufacture thick solid sections because they are more stable and less expensive to machine. To avoid deformation or fractures when machining a thin wall, use multiple passes at low cutting depths. Thin features are also highly prone to vibrations, so machining them accurately is challenging and increases machining time considerably.
To minimize cost:
For metal parts, design walls thicker than 0.8mm&#;the thicker, the better.
For plastic parts, keep the minimum wall thickness above 1.5mm.
Good to know: The minimum wall thickness that can be achieved for metals is 0.5mm. For plastics, it is 1mm. Assess the machinability of such features case by case.
Important: Thin walls are often an issue when placing holes (and threads) very close to a part&#;s edge. Take this into account when designing for CNC machining.
Including threads that are longer than necessary can increase the cost of CNC parts because special tooling may be required. Threads longer than 1.5 times the diameter of the hole do not enhance a connection&#;s strength.
To minimize cost:
Design threads with a maximum length of up to three times the hole diameter.
For threads in blind holes, add at least half of the diameter of the unthreaded length at the bottom of the hole.
Holes can be CNC-machined quickly and to great accuracy using standard drill bits. For non-standard sizes, an extra machining step is required, which drives up cost.
When possible, use through holes instead of blind holes because they are easier to machine.
Limit the depth of holes to four times their diameter. Deeper holes (up to 10 times the diameter) can be manufactured, but they are likely to drive up cost because they require more time to machine.
To minimize cost:
Design holes with a diameter that is an increment of 0.1mm for diameters up to 10mm. For those above 10mm, use an increment of 0.5mm.
When designing in inches, use conventional fractions of an inch or refer to a fractional-inch drill bit sizes table.
As an added bonus for cutting down on lead times, try using standard thread sizes in your CNC designs. This will reduce the time it takes to machine your parts, which will also lower costs.
Defining tight tolerances increases the cost of machining a feature, so it should only be done when absolutely necessary. If a specific tolerance is not defined on the technical drawing, the parts are machined using the standard tolerance (± 0.125mm or better). This is sufficient for most non-critical features.
To minimize cost:
Only define tighter tolerances when it is absolutely necessary.
Define a single datum (e.g. the cross-section of two edges) as a reference for all dimensions with tolerances.
Pro tip: Use Geometric Dimensioning and Tolerancing (GD&T) in technical drawings to reduce the cost of CNC machining. GD&T includes features such as flatness, straightness, circularity, and true position. It often defines a looser tolerance, although it requires advanced design knowledge to apply effectively.
Design parts that can be machined in as few machine setups as possible. Ideally, use only one setup. For example, a part that has blind holes on both sides must be machined in two setups because it needs to be rotated for access to both sides.
Rotating or repositioning a part drives up manufacturing cost, as it usually must be done manually. Moreover, intricate geometries might require a custom fixture, increasing costs. Especially complicated geometries might require a multi-axis CNC system, also increasing cost.
Consider separating the part into multiple geometries that can be CNC-machined in a single setup and that can be bolted or welded together later. This also applies to parts with very deep pockets.
To minimize cost:
Design parts with a simple 2.5D geometry that can be manufactured in a single CNC machine setup.
If this is not possible, separate the part into multiple geometries that can be assembled later.
Small features with a high width-to-height aspect ratio are prone to vibrations and are thus difficult to machine accurately.
To minimize cost:
Design features with a width-to-height aspect ratio of less than four.
Add bracing support around small features or connect them to a wall to improve their stiffness.
Adding text on the surface of a CNC-machined part can significantly drive up cost because it requires additional machining steps, which takes more time. Surface finishing methods, such as silk screening or painting, are a more cost-effective way of adding text on the surface of a CNC-machined part.
To minimize cost:
Remove all text and lettering from your CNC-machined parts.
If text is necessary, choose engraved over embossed lettering.
Use a minimum of size-20 sans serif font (e.g. Arial or Verdana).
Machinability refers to the ease with which a material can be cut. The higher the machinability, the faster a material can be CNC machined, thereby lowering cost. Machinability depends on the physical properties of each material. Typically, the softer and more ductile a metal alloy, the easier it is to machine.
C360 brass is the alloy with the highest machinability, allowing for high speed machining. Aluminum alloys (e.g. and ) can also be machined very easily, though require slightly lower speeds.
Stainless steel has 10 times lower machinability than aluminum and will take at least twice as much time to machine. Different steel grades have different machinability. For example, 304 stainless steel has a machinability index of 45 percent, while 303 stainless steel (an alloy with very similar chemical composition) has an index of 78 percent, making it easier to machine.
The machinability of plastics mainly depends on their thermal properties and stiffness because they are prone to melting and bending during machining.
POM (Derlin) is the easiest plastic to machine, while ABS comes in a close second. PEEK and nylon 6 are common engineering plastics that are more difficult to machine.
To minimize cost:
If you have options, choose the material with better machinability, especially for larger orders.
The price of the bulk material is another factor that can greatly affect the cost of CNC-machined parts.
The table below summarizes the price of metal alloys and plastic materials commonly used in CNC for a sheet with dimensions of 6'' x 6'' x 1'' (or approximately 150 x 150 x 25mm).
Source: McMaster
Aluminum is by far the most cost-effective way of creating metal prototypes because of its low cost and very good machinability.
Metals that offer greater machinability, such as stainless steel 303 and C360 brass, cost more and are thus better suited for larger volume production. In this case, economies of scale come into play because the higher material cost is outweighed by the much shorter machining times.
When it comes to plastics, ABS, nylon, and POM (Derlin) cost approximately the same as aluminum . They are more difficult to machine though, so expect a higher cost. PEEK is very expensive material and should be used only when absolutely necessary.
To minimize cost:
Choose a material with low bulk price, especially for low-volume orders.
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Surface finishes improve the appearance of CNC-machined parts and their resistance to harsh environments, but they also drive up cost. Requesting multiple surfaces finishes on the same part further drives up cost because it requires extra steps (for example, masking the surfaces). An article summarizing the benefits of each surface finish for CNC parts can be found here.
To minimize cost:
Choose the &#;as machined&#; surface finish.
Request multiple surface finishes only when absolutely necessary.
The size of the blank&#;that is, the stock material&#;may impact the overall cost. As a rule of thumb, the blank must be a minimum of 3mm larger than the end part. To ensure accuracy, some material must be removed from all edges of the part.
As an example of how the blank size affects pricing in CNC, consider designing a part that has an envelope of 30 x 30 x 30mm. These dimensions would require a larger blank to be used, which in this case is typically cut from a sheet that is 35mm thick. If the part had an envelope of 27 x 27 x 27mm, however, then a 30mm sheet could be used, saving a lot of material.
To minimize cost:
Design parts that have a dimension 3mm smaller than a standard blank size.
In CNC machining, quantity greatly affects unit price. This is because start-up costs are relatively high and, when quantities are small, they represent a big percentage of the cost. With large quantities, however, the per-unit costs decrease.
In the graph below, we plot the average unit price of 12 different parts machined in stainless steel 304.
The drop in unit price is almost exponential, meaning that even increasing the volume from one to five can cut the unit price in half. Also, ordering very high volumes (> 1,000 parts) reduces the unit price by five to 10 times.
To minimize cost:
Take advantage of economies of scale by ordering higher quantities.
In conclusion, keep your CNC machining simple.
Complexity has a high price in CNC. Geometries that require special tooling or fixtures, multiple machine setups, or special materials cost more.
So to keep costs down, before you submit an order for quoting, ask the following questions:
Is my part optimized using designing for machinability guidelines?
Are all features in my model absolutely necessary? Or can I remove or simplify while retaining the part&#;s full functionality?
Can my design be separated into multiple parts that are easier to CNC machine and assemble later?
Is there a way to modify my design to eliminate the need for multiple machine setups or special tooling?
Is there a material that is less expensive or easier to machine that can fulfill my design requirements?
The capabilities of CNC machining are constantly expanding. For example, recent advances in CNC tooling enable modern CNC systems to thread holes throughout their length, and holes of any diameter can be CNC machined, without a significant effect on the price, by using a plunging CNC tool and using profile interpolation (i.e. a helical tool path).
In this article, we focused on general designing-for-manufacturability tips that have a universal application, no matter what CNC system is used. Interpret these tips as general good practices that can help you design parts more efficiently.
If you found this article useful and want to take it offline, you can download our essential CNC machining cost reduction checklist.
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&#; Factors Affecting CNC Machining
1- Rounded Internal Corners
2- Limit the Use of Tight Tolerances for Cheap CNC Machining
3- Use Less Expensive Material in CNC Milling Machined Parts
4- Avoid Multiple Finishes
5- Order Larger Quantities
6- Avoid Deep Pockets
7- Expand Thin Walls
8- Limit the Length of Threads
9- Optimize Tapped Holes
10- Leverage Standard Drill Sizes
11- Split up Complex Parts
Conclusion
Factors Affecting CNC Machining
The costs of CNC Machining also vary and certain factors may cause high rates of CNC machining components and machines. Some of these factors are:
These are the main factors that can affect the CNC machining process and machine costs. So, it would help if you made the right choice to create CNC machining elements with less costs. It makes CNC machining projects and production more affordable. The use of specific machines like 3-axis or 5-axis CNC machines in cnc process can increase its rate as CNC machines shop charge you hourly for various machines. The price of CNC 5-axis machines is more costly than 3-axis machines. Following are the simple tips by which you can reduce the CNC machining costs and make the CNC machine process cost-effective.
1- Rounded Internal Corners
The rounded internal corners can automatically create the CNC machining part and devices like milling cutters or end mills. If this radius is more expensive, the instrument will require fewer passes of a milling lathe to remove the materials. On the other hand, small instruments are necessary on the lathe axis if the internal radius is narrow. Due to the narrower radius, the tool will need to make more passes to remove material. It may cause the breakage of the tool or may cause deflection- a sign of failure. It will ultimately result in a more CNC machining time, which leads to a high price. To reduce this high expense, you must make sure that the inside corner range of radius of your CNC design part should have a length to diameter in the range of radius 3:1 or less than 3:1. It prevents tool and machine shop breakage, thus fixing the time.
2- Limit the Use of Tight Tolerances for Cheap CNC Machining
Usually, the tolerance of the CNC machining part is +/-0.127mm. In most cases, the tolerance can be +/-0.05mm. The tight tolerance of the CNC machined part design can enhance the machining timing and thus resulting in a high rate of part design. Complex design requires more materials and more rate. Specifying the critical features or the surfaces of the CNC machined part and process with the numerical features can reduce the CNC machining timing and, therefore, can make the CNC machining part cheap.
3- Use Less Expensive Material in CNC Milling Machined Parts
The cost of the machined part is greatly dependent on the materials used in a project. While manufacturing the CNC machining parts, the more complex and costly materials such as , stainless steel, prove more expensive than soft ones aluminum. Material such as aluminum is more easy to cut, so it takes less time to cut material. CAD file preparation and bulk material such as aluminum can increase the manufacturing rate, and high-quality parts need more time so need more time and ultimately increase the budget. On the other hand, you can easily cut the soft material in less time. Thus, less machining time by using the soft material can reduce CNC pricing and make CNC machining parts affordable. Moreover, the high-cost tools require cutting and breaking the more rigid material. In contrast, tools with low price may require breaking the soft material, which can make CNC machining services cost-effective and reduce the CNC machining price.
4- Avoid Multiple Finishes
Usually, the finishing and manufacturing of the CNC machining parts consider vital because they may help improve the appearance of the CNC machined parts. It may also protect against the harmful effects of the harsh surrounding. Multiple finishes take more time to machine, and the price of CNC machines and services can enhance. So avoid multiple finishes and only use them when you essentially require them for your process and CNC machining components, whether they are metal, aluminum pieces, or plastic pieces. It may include the treatments such as anodizing, heat treatments, or specialized coatings to increase the quality of the CNC components. You may consider multiple finishing a good idea, but it increases its rate. So, to reduce the pricing of manufacturing and instrument for your projects and increase the quality of machine components, you must avoid the numerous finishing of your CNC machining components and use cheap materials like aluminum. The use of an as-machining finish instead of multiple finishing can help in reducing the expenditure of metal, plastics, aluminum, steel pieces and materials and increase the quality.
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5- Order Larger Quantities
For the proper running or working of the CNC machining, you can combine the multiple operations. But, instead of combining various operations, CNC machining such as laser cutting still requires adequate setup and programming. The price of the machining components is directly dependent on the number of factors that you order. The production efficiencies may increase by ordering large quantities of the same machining elements. It greatly helps to reduce the price of CNC and components per piece.
6- Avoid Deep Pockets
The deep pockets in machining elements significantly affect its price. The deep pockets in CNC increase the price of the machining parts. You may need to remove a lot of material such as steel, plastics, and stainless steel, aluminum from the parts to achieve deep pockets. So, it is a time-consuming process, thus ultimately increasing the price. Moreover, acquiring a deep pocket in CNC milling may need special instruments such as an end mill because the mechanism may break while getting deep pockets. Some tools commonly used to obtain deep pockets in machining parts are costly, thus increasing mill costs. So, avoiding the deep pockets in machining parts can play a key role to control cost.
7- Expand Thin Walls
The thin walls of the machining parts can increase the price due to its lower tolerance capacity. As we know, the thin walls have lower tolerance capacity, so they may break if a little more force can apply to them during the machining process. Moreover, during the CNC machining process, the shape of the CNC machined parts may change, and CNC machined parts may become distorted. It results in getting the new features that result in an additional price, thus increasing the price of machine service. So to avoid this problem and reduce the price and machining service, you must avoid the use of thin machining parts. Instead of thin-wall parts, you can use thick wall parts that cannot be easily broken or distorted during the machining process; this results in a rate reduction.
8- Limit the Length of Threads
The cost of the stainless steel and aluminum machining parts is also greatly affected by the length of the threads. The deep threads in the machining parts increase the price of the CNC machining parts and also affect their quality. On the other hand, avoiding deep pockets reduces the price. Suppose the length of the thread is more than 1.5 as compared to the diameter of the hole. Then, it results in a weak connection and can lose the connection quickly. If the length of the thread is much longer than the requirement, you may need special instruments in creating them, thus causing the additional rate. To reduce the price of the CNC machine parts in the production, you must design the threads of appropriate length. While you design the part, make sure that the size of the thread should be three times the diameter of the hole. You must make sure that the length of the thread must be an additional half diameter in blind holes. Thus choosing the exact length and limiting the thread length can reduce the price of the CNC machining process and projects.
9- Optimize Tapped Holes
The price of the CNC machining service such as laser cutters and projects can also increase due to the tapped holes in the machining parts. The tap size and the depth of the tapped holes are the main factors that directly affect the price of the milling machine and mill. Like the length of the threads in CNC milling, if the size and depth of the holes are not appropriate and do not match the requirement, it increases the machining parts price. The depth should limit to three times the diameter of the hole. Similarly, you must stick to a standard tap size while designing the machining parts, whether you are designing prototypes, aluminum components, or stainless steel parts. The mill machine requires more time to perform this function. Limiting the depth and sticking to a standard tap size can help significantly reduce the price of the machine and provide you best quality products and prototyping parts.
10- Leverage Standard Drill Sizes
CNC machining projects and parts' price is also affected by the instruments, materials, and sizes of the drills in the machining parts. The larger or smaller sizes of the drills than the required size in the machining parts significantly increase the price of the machining parts. So you must make sure to use a standard drill size to prevent any loss. Make sure not to use instruments such as reamers for finishing the hole sizes because it leads to non-standard dimensions. You must keep the hole sizes to the standard number, letter, or fractional drill sizes.
This standard size, number, and letter can help reduce the machining timing and automatically reduce the CNC machining service and parts price of aluminum and titanium. The price may also affect by the depth of the holes in plastic, stainless steel, aluminum, or metals components. The holes deeper than 10 times the diameter can increase the pricing of CNC machining.
11- Split up Complex Parts
The complex machined parts can increase the price of CNC service to a certain level as more resources are required for this task. As we know, complex and costly materials may require more complicated features, and using more axis-like 5-axis machines, milling machines, or 3D printing, cause more price for your production. The use of complex machined parts requires custom features, time and a 5-axis mill which makes the CNC machining process and service more costly. Less use of material such as metals, plastic, aluminum, titanium can make a big difference. Removal of material from the mill center takes more time for milling and makes delivery late.
Due to the complex milling process and material, there is a need for various CNC machines, which automatically increase and control the pricing of CNC milling and services.
Conclusion
So to make CNC services, custom and rapid prototyping cheap for industrial applications., the complicated CNC machining parts should design using appropriate 3D printing, online capabilities, tools, and cheap materials. Use of a 3-axis machine, request of a quote to estimate budget, and cheap materials is key to a price reduction and rapid delivery for CNC plastic and steel machined part. It is helpful for the custom metal and plastics parts and material that requires additional machining time, such as the custom metals parts with deep pockets, thus reducing the price of these precision parts and making them cheap. But by following the above simple tips, you can save your machining time production price and reduce the rate of CNC machining. It will be better to contact a CNC machine shop to get a free online quote for your projects.
Some CNC machine shops also provide online quotes for CNC machined part, so you can request a free, instant quote for CNC part and get an estimated budget for your CNC prototyping production. The use of more axis machines for CNC part may prove more costly. Worthy Hardware is a certified CNC machining shop and no one can beat us in high-quality part and cheap materials, manufacturing CNC parts. Your satisfaction is our priority for the optimization of your parts and design. Request a free quote and know our capabilities and resources. We have a wide range of materials such as steel, plastics, titanium,wooden and provide full-time support and quote to our customers.
For more information, please visit stainless steel cnc machining parts.
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