Manual machining requires direct control and skill, suitable for unique, low-volume tasks. CNC machining uses computer programs for precise, high-volume production, reaching tolerances up to ±0.0001 inches, reducing errors and material waste.
Control Method
Manual machining is, naturally, carried out manually by the operator physically turning cranks, handwheels, levers, and adjusting various devices using hand and eye. Skilled machinists can “read” the working material and cut, making timely adjustments based on feedback they are getting. They may feel a slight change in resistance of a material while cutting and slowing down or stopping to adjust. If a component is machined well manual machine, may produce lesser vibrations and disturbances than its CNC analog. CNC machining is able to reproduce a piece perfectly each time because software programs of CNC machines drive cutting tools as well as the workpiece.
The computer in CNC machine reads design and executes the cutting following it in movements to create a product that can be precise to 0.0001 inches. Overall, CNC machines make complex designs with much higher precision and speed repeatably. For example, these typically very complex components are made from a single piece of stock, aerospace manufactures may need of them, and each piece in that set must be the same because they all go into the same aircraft, that is impossible with manual machining. Another example could be an automatic transmission valve body that is designed to avoid mistakes between valves, springs, or fluid flow.
Just for instance, the same piston is not made exactly the same with manual machining. The analog of it, CNC machining, “reads” the parameters of the piston and is then able to reproduce it as precise as wanted. That is economical for both time and material. The example of a job shop shows that shift from manual machines to CNC machines increases output by 50 percent. Conversion from a manual to CNC practice creates an artificial demand for machinists who are able to program and maintain these CNC machines, rather than just operating machines as before. CNC machines cost 10 to 30 times than manual machines, however, they pay off in a high-volume production when the lifespan of the machine is calculated.
Precision and Consistency
In manual machining, the precision of parts is defined by the skill and ability of the machinist to replicate those results consistently. Generally, this level of precision is ±0.001 inches, which is sufficient for many applications. However, there are industries where it may be insufficient, such as medical implants or aerospace parts. The latter industry has tolerances around 0.0005 inches, as these parts are generally very large, and such small deviations may still result in catastrophic failure. In other parts of the manufacturing process, the tolerance is already 0.0001 inches. As a result, CNC machining, which is guided by incredibly detailed and precise computer programs, becomes the solution, as the new technology allows for these levels of precision to be met consistently.
The best example of where CNC machining is necessary and beneficial can be when considering the manufacture of smartphone components. In such cases, the parts being produced are not singular, but multiple and sometimes reaching millions of identical parts. They must also fit within the existing parameters of the device in question. Every microphone slot, screw hole, and connector must be exactly the same, as otherwise, the assembly process will be overly difficult, and the final product will be low quality. Mistakes in these parts can make the device not durable, too as outer components will not fit well with each other.
Another reason why this decision is beneficial is the effect of CNC technology on the errors related to human fatigue and interpretation. Manual operations are affected by fatigue, and a manual machinist will not operate considerably differently over the course of an 8-hour workday in ways that they may not even notice. In this way, the dimensions of the final product and its quality will differ. Yet another benefit of CNC machines is the cost reduction that results from the reduced waste. The setup for both types of machining can be expensive, with CNC requiring both the equipment and the training for the operator. However, once the setup is complete, the speed, reduced waste, and other factors all result in savings. A typical CNC setup will reduce waste from cutting material by as much as 20%, as the patterns cut by the more accurate machines are also more efficient.
Complexity and Capability
Manual machining is often best for one-off work or situations where the expected quantity of parts is too low to justify the setup of more complex systems. It shines when each piece can be unique, such as in a custom motorcycle or automotive workshop, when individual components may require specific, bespoke enhancements to fit together. More generally, manual machining allows the machinist to quickly change course as required, without the need to reprogram the system, a major part of CNC work. CNC machining can be seen as a significant expansion of the services offered by a shop. CNC machines usually operate on several axes, most often on 3, 4, or 5 axes, which allows them to produce parts with more complex geometries than manual machines. For example, many aerospace components require the inside of channels and undercuts, impossible to cut as accurately using a 5-axis CNC machine with the same setup.
Perhaps the most important technological innovation enabling the use of CNC is the system’s ability to automatically switch between different tools. This is what enables such machines to carry out many different operations in sequence, which would require multiple setups or tool changes in manual machining. The alternative is to carry out multiple operations without removing the piece from its setup, which leads to tremendous time savings on top of greater precision, as there is no need to ensure the same measurements and angles on multiple workholding setups. For example, CNC is often used in the production of electronic housings, which require precise slots for components and holes for fastening screws, all of which must be done precisely. The holes, in particular, must be smooth and well-positioned, which a typical machinist would be unable to replicate with enough accuracy if they produced hundreds or thousands of housings by hand. However, CNC machines make short work of the task, keeping them exact across the whole production run. CNC machines are also designed to work with a wide variety of materials, from the softest plastics and woods to much harder metals such as titanium and stainless steel. They do so with equal precision and ease by adjusting the cutting speeds and feeds as automatically arranged in the program, allowing for optimal tool life and material use.
Speed and Efficiency
First and foremost, CNC machining far surpasses manual machining in both speed and efficiency. Through the use of advanced technology, CNC machines can expedite production throughput. For instance, CNC machines can run for an extended duration, even 24/7, with little supervision. In comparison, manual machining requires constant human intervention and suffers when the operator becomes too fatigued and has to call it a day. Specifically, the speed of CNC machines is clear when analyzing the production time of complex parts. A CNC machine could produce a complex part with multiple drill holes, cuts, and threads in a matter of minutes. This same part could take hours, if not an entire day, manually because the operator would need to manually change tools, set up the part, and make precise adjustments. For instance, producing a custom gear on a CNC machine may take 30 minutes. Meanwhile, producing the same part may take over three hours of manual work on a lathe, assuming the operator could make the intricate design and cut 10 times slower. Furthermore, CNC machining offers an additional benefit of high repeatability: once a program is verified, multiple parts can be produced without deviation. Repeatability is not possible in manual machining since no two steps require the same exact force or cutsimator. This means that less time would be spent on quality control and adjusting pieces, improving overall efficiency. Finally, CNC machines generally have optimized tool paths that can used the maximum material and the minimum of waste. The benefits include lower costs, decreased prices per unit, and decreased scrap. As an example, the use of CNC machining can increase material utilization by 20% for automotive OEMs. The efficiency results from a better optimized tool path in the CNC programming. Finally, less time is spent in setting up the work. Although CNC machines require some setup due to initial programming, the production of additional parts does not require additional setup. The setup work ends when the program is ready to be executed. In contrast, manual machining often requires a re-calibration, a new setup, or a tool change every part.
Cost
To evaluate the difference in costs between manual and CNC machining, it is necessary to look at both the initial investment and the operational costs. The façade of the CNC machine is higher – while the price of new equipment will depend significantly on the type of the machine, its capabilities, and complexity, a basic 3-axis CNC milling machine will likely cost about $30,000, and a 5-axis machine would cost over $100,000. In contrast, a new manual milling machine would be a more affordable $5,000 to $15,000, which is already too high a price for a workforce tool and explains why there are so many old devices still in use.
At the same time, the operational costs are also very different for the two machining methods. The manual operation requires a worker of very high qualifications, often compensated very well, especially in areas of higher costs of living. In addition, the work is bound to be much slower and less precise; it results not only in the workforce wages being higher due to the time spent but also in many other additional costs. The precision becomes especially important, as the parts may not fit or need to be reworked and cleaned more to ensure this. This leads to waste materials, even more so in the instance when the parts are reworked and then declined and added to the waste anyway, further increasing the expenses, as the waste materials must then be managed.
Even more, to ensure the quality of the product despite these costs, additional quality control measures may be necessary. All these costs are reduced or eliminated by CNC machining. In high-volume production, the CNC machines’ high speed and precision allow for much lower per-part costs, with waste all but nonexistent. The CNC can also work unattended in the lights-out manufacturing, where no workers are present overnight, reducing the workforce prices further. The advantage becomes more straightforward to see when comparing two specific examples.
The automotive industry is one of the areas where CNC machining has provided striking benefits by cutting the parts’ production time. A custom engine part to be tweaked, reworked, and created in especially high tooling quality in a manual workshop out of a metal billet would take around 2 hours of direct labor to create. In a CNC machine, the value of the part’s exact dimensions is created through a design to program the machine, which takes some time to ensure it is accurate; then, the machine itself would operate with mere oversight for the production time, which would likely take around 20 minutes.
It is also important to note that the need to re-calibrate and maintain manual machines and replace them when worn out further increases their cost, meaning that a relatively high lifetime cost of at least $100,000 overall for a CNC machine versus $30,000 for a manual machine is not only justified but also likely much more pronounced in reality, as manual machine would likely wear out much faster.
Skill Requirements
The skill sets required for manual and CNC machining are different in nature and each requires different specializations. Manual machining is heavily reliant on the operator’s experience and actual, physical control over the machine tools. The person needs to have an in-depth understanding of the materials that are worked on, specific tool behavior, and the impact that manual adjustments have on the product. Experienced manual machinists can “feel” the process of cutting and immediately adjust it if necessary. This level of skill is gained through years of experience and is adequately applicable in custom fabrication and repair work, which necessitates a degree of adaptability and requires the machinist to be able to properly work with atypical materials.
CNC machining is more reliant on technical skills more closely related to computer and, sometimes, engineering disciplines. The operator must understand how to read and interpret the outputs of CAD and CAM systems. Additionally, a CNC machinist must have good programming skills and be able to program CNC machines or specifically, write and use G-code to command the machine’s movements. This is important to be able to set them up for a specific, often complex, production run, and any precision or even interpretation mistakes can result in a faulty product emerging from the assembly line.
The training for CNC operators can vary greatly depending on the exact position but it typically includes a degree, at least, of formal education in machining principles and CAD/CAM software, as well as direct hands-on experience with CNC machinery. Training such as these is often provided by specific technical schools and community colleges, who recognize the demand for a tailored education in the field.
Part of training in the field includes the ability to optimize production workflow, which includes not only programming but also the ability to choose the correct combination of tools and materials that will allow the machine to produce more components while being less prone to inefficiency or breakdown. In a realistic scenario, it might make a difference between a CNC machinist being capable of producing a large quantity of tightly specified and potentially complex engine parts needed for a modern vehicle, or not.
