**Processing Ultra-Precision, Low-Roughness Parts with a Conventional Grinder**
Source: Bearing Network | Time: March 7, 2014
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In many large engineering machinery manufacturing plants, components with surface roughness as low as Ra 0.02–0.04 μm and dimensional accuracy of H4–H5 are typically processed using high-precision grinding machines. However, most construction machinery repair workshops do not have access to such expensive equipment. This makes it challenging to achieve ultra-precision and low-roughness finishes on journal parts.
To address this challenge, we conducted extensive experiments on the existing M131W cylindrical grinder. Through necessary testing, scraping, and adjustment, we were able to achieve excellent results by dressing and fine balancing the grinding wheel. This process allows for the formation of numerous contour micro-blades on the abrasive grains, enabling the production of ultra-precision parts with accuracy ranging from H4 to h6 and surface roughness between Ra 0.02 and 0.04 μm. The method is simple, efficient, and yields impressive results.
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### **Ultra-Precision Grinding Mechanism**
Super-fine grinding is achieved by creating multiple equal-sized abrasive micro-blades on the surface of the grinding wheel. These micro-blades cut away thin layers from the workpiece surface, effectively removing minor defects, trace shapes, and dimensional errors. When the grinding amount is appropriate, the resulting surface exhibits extremely fine cutting marks, leading to very low surface roughness.
Additionally, during non-flame light grinding, friction, sliding, polishing, and calendering effects further reduce the surface roughness, enhancing the finish quality.
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### **Inspection of the Ordinary Grinding Machine**
To achieve surface roughness of Ra 0.02–0.04 μm on a modified grinding machine, several key components must be inspected and adjusted:
1. **Bed Guide Inspection**
- V-shaped guide rail straightness in the vertical plane should not exceed 0.01 mm per meter.
- In the horizontal plane, the straightness should also not exceed 0.01 mm per meter.
- The sliding saddle rail's straightness over 250 mm must not exceed 0.02 mm, with a touch point density of 12–14 points per 25×25 mm area.
2. **Sliding Saddle Rail Inspection**
- V-shaped guide rail straightness should not exceed 0.01 mm per meter.
- Flat guide rail non-parallelism must be within 0.02/1000 mm across the entire length.
- Touch point density requirement is 10–12 points per 25×25 mm area.
3. **Grinding Wheel Spindle and Bearing Adjustment**
- Adjust the gap between the grinding wheel spindle and bearing bush to 0.0025–0.005 mm.
- Scrape the bearing surface to achieve 12–14 touch points per 25×25 mm area.
4. **Balancing the Grinding Wheel Spindle Motor**
- The motor must be balanced to minimize vibration.
- The grinding wheel should be balanced twice—once after diamond dressing and again after oil stone or rough grinding.
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### **Two-Step Dressing of the Grinding Wheel**
To achieve Ra 0.02–0.04 μm surface roughness, two-step dressing is essential:
1. **Diamond Pen Refinement**
- Use a diamond pen to refine the wheel, followed by a fine wheel for finishing.
- After finishing, use a TL60#ZR1-ZR2 grinding wheel (φ100mm) for additional dressing.
- Mount the wheel on a mandrel, finish its outer circle on a lathe, then dress it on the grinding machine.
- Adjust the head frame speed to 80–100 r/min, feed rate to 0.002 mm, and reciprocating speed to less than 0.3 m/min.
- Ensure coolant is full to wash away debris and prevent contamination.
2. **Fine Stone Repair**
- Finish with a sharp single-grain diamond pen.
- Use an oil stone to further refine the wheel, ensuring more contour micro-blades are formed.
- During dressing, maintain uniform sound and check for any irregularities.
- After dressing, brush off any floating debris and ensure coolant is clean and filtered before grinding.
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### **Grinding Parameters**
| Parameter | Value |
|----------------------------------|---------------------------|
| Wheel Speed (m/min) | 4–10 |
| Worktable Longitudinal Feed (mm/min) | 50–100 |
| Grinding Depth (mm) | 0.0025–0.005 |
| Number of Lateral Feeds | 1–2 |
| Worktable Reciprocation (times) | 4–6 |
| Radial Grinding Allowance (mm) | 0.003–0.006 |
| Achievable Surface Roughness | Ra 0.02–0.04 μm |
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### **Precautions and Common Issues**
1. **Workpiece and Wheel Contact**
- Listen for a "cymbal-like" sound when the workpiece touches the wheel.
- Use coolant with slightly higher concentration than saponification solution, and ensure it is filtered before use.
- Feed at 0.005 mm per double stroke until no sparks appear.
2. **Avoid Thermal Expansion**
- During summer, avoid excessive heat from lighting, which can cause workpiece expansion.
3. **Coolant Quality**
- Ensure coolant is clean; if contaminated, filter or brush off floating sand.
4. **Burn Marks**
- Avoid burns by maintaining sufficient coolant flow and avoiding excessive feed rates.
5. **Surface Ripples**
- Fine ripples may result from loose spindles or motor vibrations. Adjust accordingly based on specific conditions.
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**Related Bearings Knowledge:**
- Five Principles of Normal Bearing Operation
- How to Carry Out Bearing and Shaft Cooperation Detection
- Rolling Bearing Fundamental Knowledge
- Bearing View Method
- INA Bearing Common Faults and Solutions
This article was originally published on China Bearing Network.
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