Choosing the correct shim profile depends on two main factors: the size of the machine foot and the diameter of the anchor bolt. The shim must provide adequate coverage of the foot while allowing the bolt to pass through the slot without interference.
As a general rule, the shim should cover at least 80% of the machine foot contact area. This ensures even load distribution and prevents localised stress concentrations that could lead to soft foot conditions.
Profile Selection Table
| Profile | Dimensions | Slot Width | Typical Bolt Size | Suitable For |
|---|---|---|---|---|
| Profile A | 50 × 50mm | 13mm | M12 to M14 | Small motors, fractional HP pumps |
| Profile B | 75 × 75mm | 21mm | M18 to M20 | Medium motors, standard pumps |
| Profile C | 100 × 100mm | 32mm | M24 to M27 | Large motors, process pumps |
| Profile D | 125 × 125mm | 45mm | M36 to M42 | Heavy industrial equipment |
| Profile E | 200 × 200mm | 55mm | M48 and above | Large turbines, heavy compressors |
Bolt Clearance Requirements
The shim slot should exceed the bolt diameter by no more than 3mm. If the gap between bolt and slot is too large, the machine foot may bend when the anchor bolt is tightened. This bending creates stress and can contribute to soft foot problems.
When positioning the shim, ensure the slot does not contact the bolt threads. Thread contact can damage the shim material and make future adjustments more difficult.
Selection Example
A motor with 80mm × 80mm feet and M20 anchor bolts would typically use Profile B shims (75 × 75mm with 21mm slot). The 75mm shim covers approximately 88% of the 80mm foot, and the 21mm slot provides adequate clearance for the M20 bolt (20mm nominal diameter).
How Many Shims Per Foot?
Three pre-cut shims should always be enough for proper alignment. In extraordinary situations, four may be needed, but this should be treated as the absolute maximum. Using excessive shims is a leading cause of “squishy foot” problems, where the shim stack compresses under load.
Each air gap between shims can compress when bolts are tightened, creating soft foot conditions after the machine is secured. Where possible, use fewer thicker shims rather than multiple thin ones. Sandwich thin shims between thicker ones for stability.
- Limit shim stacks to 3 pieces; use 4 only in extraordinary situations
- No more than 1 shim shall be less than 0.08mm thickness in any stack
- The sum of the three thinnest shims shall be 0.25mm or greater
- Sandwich thin shims between thicker ones for stability
- Use a micrometer or calliper to verify shim stack thickness before installation
- Insert shim until it touches the bolt, then pull back 2–3mm to prevent bolt threads creating burrs
- Only use shims with integrated finger tabs for safe insertion and removal
- If more shimming is needed, consider machining the baseplate
Available Thicknesses
All five profiles are available in the same ten thicknesses, supplied in packs of 10 pieces. This range allows precise adjustments from fine-tuning (0.05mm) to substantial corrections (3.00mm).
Tip: Starting Point
For new alignment work, consider starting with a 0.25mm or 0.50mm shim under each foot.