**Processing Ultra-Precision, Low-Roughness Parts with a Conventional Grinder**
Source: Bearing Network | Date: March 7, 2014
In the manufacturing of large engineering machinery, achieving surface roughness as low as Ra 0.02–0.04 μm and dimensional accuracy of h4–h5 typically requires high-precision grinding machines. However, many repair workshops and smaller facilities do not have access to such advanced equipment. Despite this limitation, it is still possible to achieve ultra-precision and low-roughness finishes using standard cylindrical grinders.
Through extensive experimentation on an existing M131W cylindrical grinder, we were able to improve its performance by conducting necessary testing, scraping, and adjustments. By dressing and finely balancing the grinding wheel, we created more contour micro-blades on the abrasive grains. This allowed us to achieve precision levels from H4 to h6 and surface roughness as low as Ra 0.02–0.04 μm. The method proved simple, efficient, and highly effective.
### Ultra-Precision Grinding Mechanism
Ultra-precision grinding is achieved through the ability of the grinding wheel to generate numerous equal-sized abrasive micro-blades on its surface. These tiny cutting edges can remove minimal material from the workpiece, effectively eliminating small defects, irregularities, and dimensional errors. When the grinding amount is properly controlled, 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.
### Inspection of the Conventional Grinder
To achieve the desired surface finish (Ra 0.02–0.04 μm), the modified machine must meet strict accuracy requirements. Key inspection points include:
1. **Bed Guide Rail Inspection**
- V-shaped guide rail straightness: within 0.01 mm over 1 m.
- Plane flatness: within 0.02 mm over 1 m.
- Contact points: 12–14 points per 25 × 25 mm area.
2. **Sliding Saddle Rail Inspection**
- V-shaped guide rail straightness: within 0.01 mm over 1 m.
- Flat guide rail parallelism: within 0.02/1000 mm.
- Contact points: 10–12 points per 25 × 25 mm area.
3. **Grinding Wheel Spindle and Bearing Adjustment**
- The gap between the spindle and bearing bush should be adjusted to 0.0025–0.005 mm.
- The bearing surface should be scraped to achieve 12–14 contact points per 25 × 25 mm area.
4. **Balancing the Grinding Wheel and Motor**
- The motor must be balanced to minimize vibration.
- The grinding wheel should be balanced twice: once after rough grinding with a diamond pen, and again after fine grinding with an oil stone or rough car.
### Fine Dressing of the Grinding Wheel
To achieve the desired surface roughness (Ra 0.02–0.04 μm), the grinding wheel must be dressed twice—once with a diamond pen and then with a fine stone. This process creates more uniform micro-blades on the abrasive grains, enhancing the cutting efficiency and surface finish.
During the first dressing, the wheel is mounted on a mandrel and finished on a lathe to eliminate runout. Then, it is dressed on the grinding machine using a slow rotation speed (80–100 rpm) and a fine feed rate (0.002 mm). The worktable should move at a low speed (<0.3 m/min), and the dressing wheel should rotate in the same direction as the grinding wheel. Coolant must be used continuously to wash away debris and prevent contamination.
After the initial dressing, the wheel surface is cleaned with a brush, and the coolant is filtered before use. During grinding, sufficient coolant must be applied to avoid burning the workpiece surface.
### Grinding Parameters
When using the M131W conventional grinder for ultra-precision grinding, the following parameters are recommended:
- Wheel speed: 4–10 m/min
- Worktable longitudinal feed: 50–100 mm/min
- Grinding depth: 0.0025–0.005 mm
- Number of lateral feeds: 1–2
- Worktable reciprocations: 4–6 times (without sparking)
- Radial grinding allowance: 0.003–0.006 mm
- Achievable surface roughness: Ra 0.02–0.04 μm
### Precautions and Common Issues
1. **Workpiece and Wheel Contact**: When the workpiece touches the grinding wheel, a distinct sound is heard, and a weak spark appears. Coolant concentration should be slightly higher than saponification solution, and it must be filtered before use. Feed should be limited to 0.005 mm per double stroke.
2. **Summer Grinding**: Avoid overheating by keeping the machine illumination away from the workpiece to prevent thermal expansion.
3. **Coolant Quality**: Ensure the coolant is clean. If floating sand appears on the wheel, it should be removed with a brush.
4. **Burn Marks**: These may occur due to insufficient coolant, excessive feed, or a dull grinding wheel.
5. **Surface Ripples**: These may result from a loose spindle or motor vibration. Adjustments should be made based on specific conditions.
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**Related Bearing Knowledge**
- Five principles of normal bearing operation
- How to perform bearing and shaft cooperation detection
- Rolling bearing fundamental knowledge
- INA bearing common faults and solutions
This article is sourced from China Bearing Network. For more information, visit [http://www.bearingnetwork.com](http://www.bearingnetwork.com).
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