JS Precision

A CNC machining centre is machining a smudge-resistant, durable 304 stainless steel food equipment can, its body with only an even matte finish. The next moment, through a series of exquisite operations, it converts the case of a 316L stainless steel watch to mirror finish.

This jump from "robust and practical" to "ultimate refinement" is not wizardry, but the end result of merging stainless steel CNC milling technology with mirror-finish finishing processes.

This CNC machining guide, which is authored based on decades of experience in CNC machining by JS Precision, will guide you through step by step in attaining the secret of mirror-finish stainless steel CNC milling parts from tool selection to parameter adjustment without all the possible pitfalls and allowing you to produce mirror-finish parts you need.

Summary of Key Answer

Comparison Dimensions	Standard CNC Milling Surface	Mirror-Grade CNC Milling Surface
Surface Roughness (Ra)	Ra 3.2 ~ Ra 0.8 μm.	Ra ≤ 0.1 μm, even Ra 0.025 μm.
Core Objectives	Meet functional dimensions, control costs.	Obtain ultimate aesthetics, reduce adhesion, improve corrosion resistance.
Process Requirements	Basic tools, nominal parameters.	Special diamond tools, highly precise parameter control, multi-step polishing process.
Cost Considerations	Lower cost, higher efficiency.	Substantially higher cost, longer processing time, very stringent requirements on equipment and experience.
Typical Applications	Internal and mechanical structural parts.	High-end luxury goods components, medical implants, high-end consumer electronics, optical instruments.

Why Is It Plausible? JS Precision's Trial-And-Error Technique Involving Stainless Steel Mirror Finishing

In stainless steel mirror finishing, only experience gained through immense practical experience is of true worth.

Over the past 10 years, JS Precision has manufactured over 6,000 mirror finish orders of stainless steel CNC machined components for four primary industries: medical, sanitary ware, luxury products, and aerospace. All of the most popular stainless steel grades, including 304, 316, 420, 17-4PH, and 18 10 stainless steel, have been machined by them.

For example, we resolved the problem of unbalanced mirror finish on 316L deep-hole components for a world's leading medical enterprise. We achieved 25 changes in tool material and spindle speed parameters to ultimately stabilize the surface roughness at Ra 0.06 μm.

We also machined 1810 stainless steel decorative parts for a luxury brand in Europe, overcoming the challenge of easily scratched edges due to polishing sharp corners, with edges of the parts maintaining uniform mirror finish with flat surfaces.

These very trial-and-error experiences in actual life have helped us understand the processing tendencies of different stainless steels and suitable situations for different processes.

This manual is not theory, it is the essence of experience from thousands of failures and successes. Each suggestion can help you avoid failures, so you can completely trust its professionalism.

JS Precision has extensive hands-on experience in stainless steel CNC milling parts mirror finishing, so we can take great care in handling various machining problems. If you have needs, provide us with your part drawings and specifications, and we will quickly develop a solution and begin service.".

What Is CNC Milling? The Foundation Of Precision Parts

To do a good job in mirror processing, first clarify what is milling - milling is essentially a machining method that removes material through rotating cutting tools, while CNC milling is a precision process that combines computer control on this basis.

Simple Definition:

CNC milling is a computer numerical control system-controlled manufacturing operation where a rotating multi-bladed cutter is used to remove material from the workpiece. The entire operation is under precise program control, with minimal human intervention.

Mastering what is milling is a prerequisite for understanding the advantages of CNC milling, as it can help us have a clearer understanding of the logic of the subsequent machining process.

Core Abilities:

It is able to manufacture CNC milling parts from as uncomplicated planar surfaces to highly complex three-dimensional shapes. From components with interconnected deep grooves to precision components with precision of 0.001mm, it can make precise production, thereby becoming the core tool to manufacture high-precision CNC machining parts.

JS Precision understands the need for mirror finishes through CNC milling and possesses 20 state-of-the-art multi-axis CNC milling machines, 10 of which are five-axis CNC machines. It enables single-setup multi-face machining of parts, eradicating clamping errors and creating a stable dimensional foundation for mirror finishes.

Choosing the Right Stainless Steel for Your CNC Milling Parts

Choosing the right stainless steel is the first step to getting a good mirror finish on CNC milling parts. Material properties will directly influence ease or hardness of subsequent machining and, ultimately, surface effect obtained.

Selection Principles: Surface finish and machinability are directly affected by the corrosion resistance, hardness, and microstructure of the material. Excess hardness can lead to tool damage and burrs, and poor corrosion resistance readily leads to rust and mirror-finish damage.

Comparison of Common Stainless Steel Grades:

Stainless Steel Grade	Core Characteristics	Applicable Scenarios	Mirror Finish
304/304L	All-purpose, good corrosion resistance, moderate cost.	Decorative parts, household appliances, general industrial parts.	Good, simple to form homogenous surface.
316/316L	Molybdenum addition, highly acid, alkali, and seawater corrosion resistant.	Surgical equipment, marine environment components, chemical equipment.	Excellent, improved mirror finish life.
420	Martensitic stainless steel, can be hardened by heat treatment.	Wear-resistant parts such as knives, valves, and bearings.	Good, must be controlled with high precision in heat treatment conditions.
17-4PH	Precipitation hardening stainless steel, high strength and hardness.	Structural components subjected to high stress, aerospace components.	Medium, must be strictly controlled in machining allowance.

Special Focus: 18 10 Stainless Steel

It is essentially a stainless steel containing 18% chromium and 10% nickel, normally grade 304 or 316 stainless steel meeting the composition specification.

Its austenitic structure being uniformed provides for consistent removal of the material when milling and polishing to produce an excellent mirror finish ability. It is generally used on CNC machining parts that have high aesthetic requirements.

Figure 1: Grade 304 is the most adaptable and frequently used stainless steel grade in machining tools.

Key Considerations Before Starting Your Stainless Steel CNC Milling Project

Before undertaking a stainless steel CNC milling project, deliberate initial thoughts can prevent subsequent rework. In CNC milling parts where the mirror finish is required, meticulous attention upfront makes a big difference.

Key Considerations during the Design Stage

1. Geometric Complexity: Excessive grooves and complex internal cavities increase polishing cost and complexity. Excessive grooves have limited space, making it hard for tools to be deep and leaving areas unpolished.

2. Sharp Corners and Rounded Corners: Use rounded corners to avert stress concentration as well as simplify polishing. The sharp corners are easily ground flat and crack.

3. Surface Quality Specifications: Clearly state the ultimate required Ra value to avoid over- and under-specifying. Over-specifying is expensive, and under-specifying is suboptimal.

Material and Post-Processing Factors

1. Material Consistency: Supply batch-to-batch material consistency for a uniform mirror finish. Batch inconsistency will affect the surface roughness after polishing.

2. Post-processing: Check whether PVD coating, electroplating, etc., are required. Mirror-finish substrate is a basic prerequisite of higher-order surface treatment, an uneven substrate will render subsequent processing worthless.

Figure 2: Internal cavity machining of engine housing for fine and uniform surface finish.

The CNC Milling Process: From Rough Stock To Mirror Finish

The CNC milling process is a gradual process, and the reasonable selection of types of milling (such as end milling, perimeter milling, etc.) will directly affect the processing efficiency and surface quality.

To obtain CNC milling parts with mirror effect, it is necessary to combine appropriate types of milling and gradually advance from rough machining to mirror finishing.

1. Roughing: Remove rapidly most of the unwanted material with a high depth of cut and feed rate, and utilize a nominal allowance of 2-5mm.At this stage, efficient types of milling, such as weekly milling, are often used to quickly remove redundant materials.

2. Semi-finishing: Improve size and shape tolerance by reducing depth of cut and feed rate, keeping error at 0.1mm, approaching final shape.

3. Finishing: Employ sharp cutting tools, low depth of cut, high speed, and moderate feed rate to produce a base surface with roughness of the order Ra 0.4 μm, a key prerequisite for mirror processing.

4. Mirror Finish: Off-line grinding or on a CNC grinder, selecting operations such as electro-mechanical/electrolytic polishing to reduce the surface roughness to below Ra 0.1 μm.

JS Precision is expert in the entire CNC milling process, from roughing up to mirror finish, keeping quality control throughout. We only need you to give us part specifications and we shall organize an experienced team to complete every stage in the process of machining so that desired results are achieved.

How To Achieve A Perfect Mirror Finish On CNC Milling Parts?

In order to achieve a perfect mirror finish on CNC milling parts, it is necessary to combine the correct polishing methods and processes. From substrate preparation to follow-up polishing, every step has stringent requirements.

Higher Quality Finished Surface

Without a surface roughness substrate (Ra 0.4 μm or less), future polish will be less effective. Tool marks or substrate irregularity will be more costly and affect accuracy.

Mechanical Polishing Path

• Oilstone/File Polish: Eliminates tool marks and micro-irregularities. Erase marks initially with an oilstone coarse, followed by a fine oilstone to sharpen.
• Progressive Sandpaper Smoothing: Gradually from 400# coarse to 1500# and finer sandpaper, eliminating previous scratches when changing.
• Diamond Paste Smoothing: The use of diamond grinding paste and soft wheels is crucial for optical mirrors. It can remove extremely fine non-evenness with a surface roughness (Ra 0.025 μm or less).

Sophisticated/Niche Processes

• Electropolishing: Removes very small peaks electrochemically, suitable for complex parts, with easy access for hard-to-reach areas and improved corrosion resistance.
• Magnetorheological Polishing: For precision parts with no fine angles, magnetorheological fluid polishing up to Ra 0.01 μm surface finish.

What Surface Roughness Can You Expect From CNC Milling Parts?

Every process has a corresponding surface roughness in CNC milling parts. It is easier to establish your needs and shun the useless effort of high-difficulty machining by using the numerical range.

Following is a clear Ra value range:

Surface Type	Ra Value Range	Appearance and Touch	Applicable Scenarios
Traditional Machining	Ra 3.2 ~ Ra 0.8 μm	Tool marks are visible, rough to touch.	Low surface requirement parts.
Good Finishing	Ra 0.8 ~ Ra 0.2 μm	No deep tool marks, smooth to touch.	Most precision parts, no need to create mirror effect.
High Gloss Surface	Ra 0.2 ~ Ra 0.1 μm	Diffuse reflection gloss, fuzzy reflections visible.	Some parts with certain appearance requirements.
Mirror Finish	Ra ≤ 0.1 μm	Begins reflecting images out of focus, touchy.	Most surfaces requiring mirror finish.
Optical Mirror Finish	Ra ≤ 0.025 μm	Resistant to reflection, no deformation, briliance.	High quality optical components, high grade medical instrument components.

Decoding The Quote: How Are CNC Milling Services Priced?

Being aware of how much CNC milling services cost can help you better control costs and avoid price disputes when collaborating. Pricing is greatly influenced by the following cost drivers:

• Material Cost: Raw material cost varies with grade. For example, 18 10 Stainless Steel will be 15%-20% more expensive than standard 304 stainless steel, and that is very specifically included in the quote.
• Processing Time: Including programming time and machine tool run time, that is the biggest variable. More complex parts have longer programming time and polishing time and contribute to cost.
• Complexity of Process: Post-processing such as mirror polishing is one of the major cost drivers for escalation, on a per person-hour basis. Electrolytic polishing is 30%-50% more expensive than mechanical polishing.
• Equipments and Losses: Depreciation on cost of five-axis machine tools, diamond tools, etc., with procurement cost and loss distributed proportionally.
• Quality Management: In-process quality inspection costs, with a number of tests to ensure effectiveness, these are included in the quotation.

JS Precision value proposition: We offer open pricing, pricing out material costs, processing time, and processes in quotes so we have clear pricing and no surprises.

JS Precision provides open CNC milling services quotes with all of the costs. After you provide part drawings and requirements, we will provide a quote within 24 hours so you have a good idea of where each expense is going.

Troubleshooting Common Issues In The CNC Milling Process

There is no means of evading difficulty in CNC milling process, especially when milling stainless steel and achieving a mirror finish. Misuse can directly affect the end quality. These are common issues and expert remedies provided by JS Precision:

• Work hardening can increase hardness, damage the tool, and crack the surface. Solution: Use sharp tools, proper feed rates, control cutting speed to prevent high temperatures from promoting hardening.
• Tool chip adhesion creates scratches. Solution: Optimize cooling parameters, use coated (e.g., TiAlN) sharp-coated tools, and keep flushing coolant away from chips.
• Irregular mirror surface affects appearance. Solution: Keep the substrate uniform, keep polishing pressure and temperature to prevent orange peel texture.
• Edge burrs affect assembly. Solution: Use JS Precision's skilled processes (chemical/thermal/manual) to deburr.

Figure 3: Burrs are actually deformed materials that remain at the edges of the workpiece in the form of thin films, which are very sharp and must be removed.

How To Select A Professional CNC Machining Parts Supplier?

Choosing a reliable CNC machining parts supplier is critical in the guarantee of the mirror finish quality of CNC milling parts and the project flow. Here is a checklist at the top level to evaluate suppliers:

• Technical Competence: Does the supplier have compatible machines (5-axis CNC, grinding machine, etc.)? Up-to-date equipment requires precision and mirror finish.
• Material Knowledge: Does the supplier understand material properties and provide suggestions? Experienced suppliers can provide cost-effective materials.
• Quality System: Does the company have an ISO 9001/13485 system and test labs? A complete system ensures compliance.
• Experience and Case Studies: Does the company have relevant industry case studies? Experienced suppliers understand needs and avoid pitfalls.
• Communication and Service: Are the engineers quick to respond and provide DFM (Design for Manufacturing) suggestions? Proper communication avoids issues and reduces cost.

JS Precision has 20 five-axis CNC machines and 15 polishing machines. It is ISO compliant, has undergone extensive industry case studies, and its engineers offer 24-hour response, making it the best supplier of CNC machining parts.

TechBullion has previously focused on JS Precision's pursuit of intelligent manufacturing platforms and optimization of supply chain efficiency. These benefits support our mirror finishing services with more efficient assistance.

JS Precision is a seasoned CNC machining parts supplier who has complete technical capabilities and a solid quality system. If you are interested in a reliable cooperation partner, please do not hesitate to get in touch with us. We will introduce relevant case studies and qualifications to ensure smooth collaboration.

Case Study: Mirror Finishing Of Stainless Steel Water Nozzles For High-End Smart Toilets

Client Requirements

A world's top bathroom brands needed stainless steel water nozzles for its newest smart toilet to be manufactured. The parts were to be manufactured out of 316L stainless steel, with complex internal flow passages and a minimum diameter of only 3mm. The exterior required mirror finishing (Ra ≤ 0.1 μm).

The greatest challenge was that the inner channels would not be polishable with common machines, and the entire nozzle needs to be corrosion-proof for human body washing liquid so as not to rust and damage the mirror-like finish when in use.

JS Precision Solution

1. Material Selection:

316L medical-grade stainless steel bars were recommended and used. The material contains molybdenum, high corrosion resistance, and superior biocompatibility and meets the hygienic requirements of the bathroom product as well as serves as the foundation for subsequent mirror polishing and corrosion resistance.

2. Accurate CNC Milling:

A five-axis CNC machining center (VMX600 model) was utilized to carry out the accurate machining of the complex internal flow passages and external geometry in one operation.

During machining, a low depth of cut (0.1mm) and high rotation speed (8000rpm) are utilized to impart the surface of the internal flow channel a Ra 0.4 μm, thus making it suitable for subsequent electropolishing.

3. Mirror Finish:

Electropolishing as the main process is employed. The components are placed in a proprietary electropolishing solution in which electrochemical action selectively removes small protrusions from the surface.

This not only treats all surfaces (including inaccessible inner walls) uniformly but also forms a dense passivation film on the part surface. Lastly, a uniform Ra 0.08 μm mirror finish is achieved internally and externally, and corrosion resistance is greatly enhanced.

Results and Value

A flawlessly finished water nozzle with extremely high hygiene standards was given to the customer with a very good appearance. In experiments, the nozzle was stable in human body cleaning solution for 1000 hours without any signs of rust.

JS Precision's integration of "CNC precision manufacturing + electropolishing" overcame the weakness of traditional mechanical polishing in handling complex internal flow channels, and won a long-term order from the customer, who subsequently also ordered more production for 5000 units.

JS Precision specializes in delivering complex mirror-finish machining solutions to CNC machining parts, such as top-end bathroom fixtures and medical equipment. If you are in need of such complex part solutions, please forward us your drawings, and we will design a customized solution and execute it to perfection.

Figure 4: CNC intelligent toilet stainless steel water outlet nozzle.

FAQs

Q1: Are mirror-finished CNC milling parts truly absolutely perfect?

While no visual imperfections are probable in macroscopic as well as conventional microscopic conditions, textures will become evident when looked at under high magnification microscopy. We ensure a "perfect" visual and tactile effect through rigorous visual inspection.

Q2: Is passivation of 18/10 stainless steel necessary after mirror finishing?

We strongly recommend doing it. Mirror finishing depletes the passivation film on the material's surface. Secondary passivation forms a thicker passivation film, significantly improving rust resistance and maintaining a hard mirror finish.

Q3: Will mirror finishing compromise the dimensional integrity of stainless steel components?

Precision mirror finishing removes very little material in micrometers. We have precise allowances and closely control the process so that the finished size fully meets the drawing specifications and not sacrifice accuracy.

Q4: What size of CNC milling part can you mirror finish?

We have from small lathes to large gantry milling machines to machine parts from millimeter to meter size. Consult with our engineers for capability details, they will recommend equipment for your part size.

Q5: Can mirror polish deep holes or narrow slots in my design?

Deep holes and slots are hard to come by, but we employ specialized equipment or electropolishing processes such that the mirror finish on these deep holes and narrow slots is identical to the other surface areas.

Q6: Besides stainless steel, what other materials is JS capable of mirror finishing?

We also have expertise in long-term experience mirror finishing titanium alloys, aluminum alloys, brass, and other metals. We tailor our processes according to the characteristics of different materials in order to provide the highest quality surface.

Q7: How do I get a complete CNC milling services quote for my project?

You simply need to provide a 3D part model (STEP/IGES), 2D plans (PDF), and the material, quantity, and surface requirements. We will generate a concise and thorough quote within a short span of time.

Q8: Will mirror finishing significantly increase cost and lead time?

Yes, since it entails more precision tools, multiple polishing processes, and rigorous quality control. It demands high skill and manpower levels. We will transparently decompose in the quotation to ensure that you get value for your money.

Summary

Stainless steel mirror finishing is an art that combines the chill of metal with the fervor of contemporary manufacturing. It's not aesthetics alone, but the quest for perfection of performance, purity, and quality. Having a partner who shares your vision is critical to your project's success.

JS Precision, as your reliable CNC machining parts supplier, has the overall capacity of bringing your designs to life—from precise CNC milling operations to high-quality mirror polishing.

Act now! Upload your design files into the JS Precision platform. We will quickly develop a solution, provide an open quote, and maintain quality throughout to make sure all CNC milling parts are of your expectation. Let us help your products dominate the market.