CNC machining is a powerful manufacturing technology for creating intricate and accurate parts. However, transforming that initial concept into reality can be a complex journey. The design is the first critical step in ensuring the best possible outcome for your project.
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Creating the 3D model of your part using CAD software needs to factor in the capabilities and limitations of the CNC machining process, as well as material properties and tolerances.
To ensure the highest quality of your CNC machined parts, we made this guide to give you tips and best practices to improve your design. These tips can lead to lower costs, an improved manufacturing process, and better parts.
CNC Machining Explained
CNC machining is a computer-controlled manufacturing method where programmed software controls complex machinery based on pre-determined movements. The wide range of machinery controlled by the software includes mills, turns, drills, and more.
Our CNC machining services offer rapid turnaround for prototypes and production parts, ensuring high quality and precision.
Our CNC machining capabilities extend to:
Machining complex geometries and shapes with high precision.
Handling both small and large parts.
Working with various materials, including metals, plastics, and composites.
Achieving smooth surface finishes and maintaining tight tolerances.
General Design Rules for CNC Machining
1. Whenever possible, design to lower the cost of labor. Optimizing designs can save time and reduce costs. For example, a chamfered edge –the transitional edge typically at a 45-degree angle – is more manufacturable than a rounded filleted edge.
Different types of edges for CNC machining
2. Make things as easy as possible for the manufacturing personnel working on your parts. One way to do that is to avoid generalized statements on drawings. Otherwise, it may be difficult for manufacturing personnel to interpret what you mean. Some of the vague comments we’ve seen include:
- “Polish this surface.”
- “Corners must be square.”
- “Tool marks not permitted.”
- “Assemblies must exhibit good workmanship.”
Notes must be more specific than this!
3. Don’t show dimensions from points in space in your designs. Instead, show dimensions from specific surfaces or points on the parts. This helps with fixture and gauge making. Importantly, this avoids potential tooling, gauge, and measurement errors.
Furthermore, dimensions should all be from one datum line rather than various points to simplify tooling and gauging and avoid overlap of tolerances.
4. The most important aspect of the design is to fulfill all functional requirements of the part. However, you can focus on making your part lighter once you achieve that.
Why focus on lightness? Fewer materials mean lower costs. Furthermore, lighter parts typically leads lower labor and tooling costs. Designers should always strive for the smallest initial raw material that fulfills strength and stiffness requirements. However, look for the raw materials on online shops to ensure they are available in the size you need.
5. Design all the functional geometries on your parts. Add functional geometries to your part, starting from your raw material dimensions and geometry. You should do this because all material extraction results in extra costs. If the part needs to be lighter, use simple geometries like cylinders and blocks and avoid free forms.
6. To further reduce costs, avoid using hardened or difficult-to-machine materials unless their unique functional properties are essential for the part. If you need to search for materials based on mechanical properties like tensile strength, hardness, or chemical composition, use this tool.
7. The MakerVerse supply chain has an extensive collection of standard, general-purpose, and special toolings. Whenever possible, design with general-purpose toolings in mind to reduce costs. Some of those more expensive special toolings include:
- Form cutters
- Countersinks other than 90°, 120° and 60°
Unless you’re dealing with high-volume productions where scale amortizes the labor and material costs of special tooling, it’s best to become familiar with all the general-purpose and standard toolings available. There are many tool catalogs (here’s one example) where you can see if the needed geometry is possible.
8. During the design phase, try to make it so that as many manufacturing operations as possible can be performed without needing to reposition the part. Doing this reduces the required handling and ensures accuracy.
9. Use international standards. Define your cutting geometry, norm parts, and processes following international standards (ISO) to ensure they can be understood and produced globally.
Furthermore, tolerate dimensions so they can be measured with standard measuring tools. Manufacturing precise tolerances requires constant dimensional checking, so design your part to be measured with micrometers, calipers, gauges, and other standard measurement tools.
10. Use stock dimensions and geometries whenever it eliminates a machining operation or the need for an extra surface.
Generally, designers consider the milled part a block where you cut the necessary functional geometries. Turning parts are seen as a cylinder where you remove the required material to create functional features.
11. Avoid interrupted cuts in single-point machining operations, as they shorten tool levels and prevent using faster carbide or ceramic tools.
12. Design your part to be rigid enough to withstand the forces of clamping and machining without suffering distortion. The forces exerted by a cutter can be severe. Same with the clamping forces needed to hold the workpiece securely. Parts with thin walls and webs, deep pockets, and deep holes requiring machining can be challenging.
Also, be sure to design the part so that a rigid cutter can be employed while permitting access to the surface.
13. Avoid complex contours as much as possible in favor of rectangular shapes for milled parts and cylindrical shapes for turning parts. Make sure that your parts can be fixed on the most standard fixtures.
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14. Design the part for easy fixturing and secure holding during machining operations. To do this, provide a large, solid mounting surface with parallel clamping surfaces to ensure a secure setup with a minimum of 12 mm high for turning machines.
15. Reduce the number and the size of shoulders, as they usually require extra operational steps and material.
16. When designing thin, flat pieces that require surface machining, allow sufficient stock for rough and finished machining. In some cases, stress relieving between rough and finished cuts is also advisable. Rough and finish machining on both sides is sometimes necessary. Allow about 0.4 mm stock for finish machining.
17. To reduce the amount of required operations, it’s best to put machined surfaces in the same plane or, if cylindrical, with the same diameter. When surfaces cannot be in the same plane, design them so they can all be machined from one side or the same setup.
18. Provide access room for cutters, bushings, and fixture elements. Design parts so that standard cutters can be used, rather than cutters needing to be ground to a particular form.
19. Avoid projections, shoulders, etc., which interfere with the overrun of a cutter. Instead, provide clearance space at the end of the cut. The space can be cast or formed to minimize machining. This will also provide a noncritical space for burrs.
20. A burr is an unwanted material caused by the CNC machining process. You should expect burrs, provide relief spaces for them, and always design to make it easy to remove them.
21. Shorten the length of your tolerances when possible. All CNC machines have a natural axial deviation defined by the producer. Going beyond that deviations requires extra setup.
22. Avoid thin and long walls, as these tend to deform. If the part is long and thin, you should design with this deformation in mind.
23. Many design for manufacturability (DFM) solutions involve splitting the part. Splitting the part generally leads to less complexity, which can unlock the benefits from many tips in this guide.
Designing for On-Demand Manufacturing
The perfect design is a crucial step in the CNC machining process, and choosing the right CNC machining services is equally important. The other important step is choosing the right place to turn your design into a finished part. MakerVerse offers a comprehensive CNC machining service that caters to rapid prototyping and high-volume production needs. MakerVerse gives you a one-stop shop platform for advanced manufacturing technologies, including CNC machining and additive manufacturing.
Using the MakerVerse platform, you can leverage the full range of technologies without investing in your machines.
Upload your design, choose your manufacturing technology and material, and receive your quote with the expected lead time. Our engineering and operations experts can personally assist you with your project.
Computer numerical control (CNC) machines, like mills and lathes, have become a fundamental part of modern manufacturing, and they don’t need much human intervention, saving companies both time and money. They’re designed to make parts automatically using a range of materials like metal, plastic, and wood, so understandably, they’re incredibly useful. Let’s have a look at the inner workings of a CNC machine to better understand how exactly it works.
CNC machines are made up of several complex components that all work together to make the machines function and quickly produce precise parts. You’ll find descriptions of each of them below.
This is basically the way CNC programs are loaded into the machine. It could be as simple as a keyboard (to directly input G-code commands), a USB flash drive with the completed program already on it, or some form of wireless communication if you want to download the program from another computer.
2. Machine Control Unit (MCU)
This component refers to a collection of software and hardware that’s responsible for reading the G-code that comes in from the input device and translating it into actual instructions for the machine and all its tools to follow. Safe to say, the MCU is one of the most important components of the entire machine as it forces the servo motors to get to work along the various axes. It also makes sure that the tools are where they should be after the movement is completed and controls the tool changers and the activation of the coolant. This is what a typical control unit looks like:
Obviously, this is generic, but it essentially refers to any tools being used in the machine, the most popular of which are usually cutting tools. Different CNC machines will tackle this differently. For example, CNC lathes keep their tools stationary and move the spinning workpiece into the machine to make the cuts. CNC mills do the opposite, moving the spinning tools toward the stationary workpiece. But, some more complex 5-axis machines will move both the tools and the part. These tools are typically kept in a part of the machine called the tool library. When a tool is needed, the machine will automatically take it from the library and start using it, before putting it back and taking anything else it might need. This is what a traditional tool might look like:
4. Driving System
This refers to the collective motors that move the tools around. In a traditional CNC mill, the bed moves horizontally (along the x- and y-axes), and the tool goes up and down (z-axis). In a CNC lathe, the tool moves in the same direction as the rotating workpiece, and goes to the outer edge as it rotates instead of across the part. Servo motors, ball screws, and linear guides keep everything moving and in sync.
5. Feedback System
This system works kind of like a backup. The driving system is incredibly accurate, but this closed-loop control system is a way to verify whether parts move to where they should. If they’re slightly off, it will adjust them with encoders, sensors that measure each component’s position. Probes also play a role; they measure the actual workpiece and ensure everything is going as planned. If any adjustments need to be made, the machine will simply make them automatically. This is what a probing tool usually looks like:
8. Headstock
The headstock is found on the left side of a CNC lathe. It houses the main drive, bearings, and gears that spin the chuck. It’s enclosed, but it can be accessed by removing some inspection panels.
9. Tailstock
This is the part of a lathe that supports one end of a long, cylindrical workpiece, while the chuck holds and spins the other end. It’s an important part of the machine that stops the material from bending during the process. It can move up and down the z-axis to accommodate different material lengths and comes in especially handy for things like shafts or screws.
10. Tailstock Quill
The quill is inside the tailstock and is a cone-shaped structure that’s aligned with the spindle and chuck. It rotates freely and keeps the material centered. For long parts, a blind hole is usually drilled into the end of the piece so that the quill can fit inside it for some support. After the tailstock is in place—close to the workpiece—the quill is pushed in by pneumatic or hydraulic pressure.
These pedals are typically only found on lathes because they activate and deactivate the chuck and tailstock quill. They basically allow the operator to load blanks into the machine and unload completed parts. CNC mills don’t usually need pedals or footswitches because the parts are already supported on the bed, and the operators don’t need to have both hands free when loading and unloading.
12. Chuck
Something we’ve mentioned a few times already, the chuck is specific to lathes and is used to grip the workpiece while it’s being worked on. The spindle keeps it rotating at a rather high speed. Generally speaking, a chuck will have three or four pneumatically or hydraulically actuated grips. Chucks that have three jaws are self-centering, which means that all the grips move evenly together. Those with four jaws are typically adjustable, with each grip able to move on its own. They’ll also have more features than chucks with fewer jaws. For instance, they’re more precise, allowing for eccentric or off-center cutting, and they’re better at handling inconsistencies with the material. This is what a traditional three-jaw chuck looks like:
13. Control Panel
This is basically the brain of the machine. It houses the input device, the display unit, the keyboard, and other control buttons. It’s typically attached to the machine but on an extendable arm so you can pull it toward you or position it where you need it.
What Is a CNC Machine?
A CNC (computer numerical control) machine is a computer-controlled automated tool that can be used to shape various materials like metals, plastic, or wood based on a set of instructions generated through CAM (computer-aided manufacturing) software. There are two commonly used CNC machines: CNC lathes and CNC mills.
What Are the Advantages of Using a CNC Machine?
CNC machines are widely used in the manufacturing industry due to their many advantages. CNC machines can work without constant operator interaction. They can also, theoretically, operate 24/7 when coupled with robotic systems to load and unload the machines. CNC machines have repeatable accuracy, which means that thousands of parts can be produced with minimal dimensional deviation from part to part. CNC machines can also produce parts with complex features that would not be possible with manual machines.
What Are the Disadvantages of Using a CNC Machine?
Like almost everything, unfortunately, yes, starting with the fact they can be crazy expensive. But in the long run (especially for large volume productions), they tend to balance out in cost compared to manual machines. Hiring people to operate the machine also isn’t cheap, because it’s quite a specialized skill set. So if you’re only planning on machining a few simple parts, you’re better off going with a manual machine.
How Does a CNC Machine Work?
A CNC machine works by automatically cutting raw material based on a set of operator-supplied instructions called G-code. This G-code contains the coordinates of the specific part features, the required tool to use, and the optimal speeds and feeds, as well as commands for when to turn the coolant on or off. The MCU (machine control unit) converts this G-code into instructions for the various servo motors and spindles in order to produce the desired part.
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