Machining is a unique substrative manufacturing technique that allows you to make a wide range of plastic or metal parts.
However, you can achieve this through manual machining or more advanced and automated systems called CNC machining.
From a machinist point of view, the two processes have unique strengths and weaknesses. However, you can only choose the right process by comparing the vital facts about each machining technique.
What is CNC Machining?
CNC machining is a modern machining approach that utilizes computer software to guide the machining process. CNC refers to Computer Numerical Control. The desired outcome of the workpiece is designed digitally via software, usually CAD (Computer Aided Design). It is then fed to the machine which performs the desired operations to achieve the design accurately.
What is Manual Machining?
With manual machining, you operate the machining tools manually without any assistance from computer systems. The outcome is highly dependent on the skill of the operator. There are various implements you utilize in the manual control of the machine such as levers, hand wheels or pedals. These allow you to determine the desired depth if cutting, feed rate and even tool position.
Difference between CNC Machining and Manual Machining
Here are some differences between the two primary machining approaches:
· Working Principle
Manual Machining:
An operator guides the machining tools typically by using controls like levers, pedals or hand wheels. They position the workpiece and guide the tool in maneuvers to determine the desired outcome. The result is highly dependent on the capabilities of the operator.
CNC Machining:
A computerized program dictates machine direction and output. After inputting a CAD design into a computer, it is converted into a digital program executable by the machine. The machine converts the program into the ideal movements automatically. It is capable of precisely capturing elements like speed, cutting depth, feed and tool path.
· Level of Automation (Programming)
Manual Machining:
Characterized by lack of programmed movements instead relying on the operator. Adjustments and determination of process parameters like feed rate, tool movement and speed are solely made by the operator.
CNC Machining:
Can be fully or semi-automated. The machine interprets the design program and executes it independently. For semi-automatic machines, human involvement can be required in instances like positioning the workpiece and changing the tool. Nonetheless, the machining process such as cutting or threading is guided by the program. Usually, these programs are in form of G-codes and M-codes.
· Skill Required for Machining Process
Manual Machining:
For higher accuracy and precise outcomes, the operator has to be highly skilled. It requires an adeptness and dexterity especially with hand-eye coordination. While mistakes can happen, experience also positively influences outcome.
CNC Machining:
Since the machining processes are directly undertaken by the machine, the skill requirements from an operator are emphasized less. However, developing the design using CAD software requires high knowledge and skill levels.
· Accuracy and Tolerance
Manual Machining:
The operator will determine the accuracy of the machining process in a typically directly proportional relationship. Additionally, accuracy and tolerance will depend on factors like state of the machine and tools. For instance, you’ll achieve lower accuracy and higher tolerance margins using a blunt cutting tool.
CNC Machining:
The accuracy using a CNC machine is dictated by the instructions and the machine’s precision level. You achieve much tighter tolerances with CNC machines. Furthermore, when working on multiple parts, you expect the same result every time.
However, the tolerance varies depending on the CNC machining process for example:
- Standard CNC machining tolerance is about ±0.13 mm
- Bilaterial tolerance is ±0.05 mm
- Unilateral tolerance is +0.02
It is also important to note that machining technique, properties of material and part complexity also determine tolerance in CNC machining.
· Repeatability
Manual Machining:
It is an uphill task to manage the same outcome when using manual machining especially when making multiple parts. Since the accuracy and tolerance are heavily influenced by the operator, repeatability will be subject to their dexterity.
CNC Machining:
You only need a single program to run multiple operations with a CNC machine leading to higher repeatability. With a CNC set-up, you can make multiple parts that are highly identical.
- Part Complexity
Manual Machining:
This approach is best suited for simple machining operations to achieve less complex shapes and forms such as cutting and drilling. More challenging operations and geometries while achievable, pose great difficulty.
CNC Machining:
Best placed for producing highly complex geometries especially those with multi-axis features. Parts with complex contours and intricate cavities challenging to execute with manual machining can be accurately replicated by CNC machining.
· Machine Setup Time
Manual Machining:
Depends with the task at hand. For simple operations and thus parts, the setup time for manual machining is short. However, when intending to perform more complex operations using manual machining, setup times will be much longer.
CNC Machining:
Generally, setup times are longer with CNC machining especially those using multiple tools. You first have to feed the programme before calibrating the machine.
· Part Machining Cost
Manual Machining:
When making simple parts in small quantities, the costs associated with manual machining are relatively low. However, these costs can rocket when working on more complex parts required in large quantities. Reason is, you will require highly skilled operator(s) which will ideally attract higher labor costs.
CNC Machining:
Using CNC machining for simple but small part volumes will result in higher part costs thanks to the programming needs. However, it is highly economical when working on large volumes of complex parts owing to higher accuracy and faster production.
· Maintenance Cost
Manual Machining:
Maintenance is generally less demanding since the machines used are simple with insignificant electronic components. Additionally, no expensive software is required with constant efforts of cleaning and lubrication sufficient.
CNC Machining:
Owing to the complexity of operations, maintenance costs are much higher. Extra care is a requirement for the multiple electronic components including sensors and motors. The computer system needs consistent updating and downtime requires specialized personnel.
· Machining Speed/Rate
Manual Machining:
Since it is dependent on the operator, typically lower speeds and feed rates are ideal. This helps in maintaining operation control through more cautionary measures.
CNC Machining:
Since the operation is automated, the machining processes are faster thanks to program optimization. There is no danger of mistakes or inaccuracies as outcome is dictated by design.
Which a better Option – CNC Machining or Manual Machining
It depends on part complexity and production volumes. The high accuracy and repeatability of CNC machining makes it ideal for parts with complex geometries required in high volumes. Contrarily, where you desire a few simple parts, manual machining is the more convenient option.
Conclusion
The most suitable operation between CNC and manual machining will depend on your project requirements. As mentioned, for low count simple parts, manual machining is ideal. However, complex parts especially when required in large numbers are better achieved with CNC machining.
FAQs
1. How does CNC vs manual machining cost compare?
Considering setup costs, manual machining compares favorably against CNC machining. However, when working on multiple parts, the latter offers you lower cost per part.
2. What are the advantages of manual machining?
- Lower initial costs
- Straightforward for simple parts and single job orders
- Demands less maintenance needs
3. What are the limitations of CNC machining processes?
- High acquisition cost
- Setup is complex
- Flexibility is limited for small job orders
- Programming and maintenance requires decent skill levels and costs
4. When is manual machining better than CNC machining process?
- When working on simple parts
- Where job orders are small and not complex
- Where you have budget limitations
