⚙️ What Are the Uses of Shims in Shaft Alignment?
In rotating machinery, shaft alignment is one of the most critical tasks for ensuring reliability, reducing vibration, and extending equipment life. A key tool in this process is the shim—a thin, flat piece of material used to adjust the vertical position of a machine. Proper use of shims ensures that the movable machine aligns perfectly with the stationary or reference machine, preventing premature wear and costly breakdowns.
🔹 Role of Shims in Shaft Alignment
- Vertical Adjustment: Shims are placed under machine feet to raise or lower the driver (e.g., motor or pump) during alignment.
- Precision Correction: They help achieve exact alignment tolerances, reducing misalignment that causes vibration and bearing damage.
- Soft Foot Correction: When angular soft foot (uneven contact between machine feet and base) is present, a shim can be cut to fill the void.
- Shims must always be clean, flat, and properly sized to ensure accurate alignment.
🔹 Types of Shims Used
- Shim Stock: Sheets of material cut to size during alignment.
- Precut Shims: Ready‑made shims, often made of 304 stainless steel, with thickness etched for easy identification.
- Custom Shims: Cut to correct angular soft foot, but only one shim should be cut—never stacked in a stair‑step fashion, which makes repositioning difficult.
🔹 Best Practices for Using Shims
1. Install Base Plate First: Shimming should only be done after the base plate installation and piping connection are finalized.
2. Limit Shim Count: Use five or fewer shims under each machine foot. A large stack of thin shims can induce soft foot.
3. Consolidate Shims: Combine thicknesses to minimize the number of shims used.
4. Material Selection: Stainless steel precut shims are preferred for durability and corrosion resistance.
5. Avoid Stair‑Step Cutting: Always cut a single shim to fill angular soft foot voids.
🔹 Why Proper Shimming Matters
- Improves Reliability: Correct alignment reduces vibration and extends bearing and seal life.
- Prevents Soft Foot: Minimizes distortion of machine frames and bases.
- Enhances Efficiency: Proper alignment lowers energy losses and improves machine performance.
- Reduces Maintenance Costs: Prevents premature failures and unplanned downtime.
🔹 Key Takeaways
- Shims are essential for vertical correction in shaft alignment.
- Use clean, flat, stainless steel shims for accuracy and durability.
- Limit shim stacks to five or fewer to avoid soft foot.
- Proper shimming ensures longer equipment life, reduced vibration, and improved reliability.