Last reviewed 30 July 2026
Unbalance correction methods: welding, drilling or weights?
In shortCorrection mass is fixed in one of three ways: welding steel plates on (steel and cast-iron rotors), removing metal by drilling or milling (high-speed rotors, armatures, spindles), or bolted removable weights. Fit half the calculated mass first and add the rest only if vibration drops without the phase flipping.
When this applies
- Physically applying a calculated correction mass
- Choosing a fixing method for the rotor design
- Steel rotors, high-speed rotors or frequent re-balancing
When it doesn’t
- Never drill blades or thin-walled casing parts
- Avoid drilling near bearing seats or splines
- Removable weights need thread-lock against loosening
Once the vibration analyser has calculated the required correction mass and the angle at which it should be fitted, the most critical practical stage begins — physically correcting the unbalance. The choice of method depends on the rotor design, the operating conditions and the accuracy required.
Recommendation from field practice: don't fit the whole calculated mass in one go. Fit half of it first (a third, on a rotor that's already close to balanced), then start the machine and check how it responds. Real machines are non-linear, and the full mass often overcorrects — the vibration stays about the same while the phase flips by roughly 180°. If the phase hasn't flipped and the vibration has dropped after fitting half, add the rest.
Method 1: welding weights on (the most reliable)
This is the most widely used and most reliable method for the majority of industrial rotors (fans, crushers, agricultural machinery).
When to use it:
- On steel and cast-iron rotors.
- When maximum fixing reliability is required.
- Under conditions of high temperatures, shock loads or abrasive wear.
How to weld correctly:
- Surface preparation: carefully clean the weld area down to bare metal.
- Choosing the weight: use steel plates of the appropriate mass.
- Tack it first: we recommend tacking the weight in place with 3–4 welds around 1 cm long — enough for a check start. Weld it in fully only once the result is confirmed, then run one more check: the weld itself adds mass (about 30–100 g, or up to 300–400 g for a heavy weld), which shifts the balance.
- Welding: weld all the way round the plate. The weld must be continuous and of good quality.
Dangerous: a correction weight that breaks off at 3000 rpm becomes a projectile. Never cut corners on weld quality!
Method 2: removing mass (drilling, milling)
This method is used where fitting additional weights is undesirable or impossible.
When to use it:
- On rotors where protruding parts are not permissible (high-speed rotors).
- On motor armatures, turbine rotors and spindles.
- When very precise correction is required.
Where you can drill:
- Purpose-made bosses on the rotor.
- The faces of discs (away from stress-concentration zones).
- Stiffening ribs (if the design allows).
It is strictly forbidden to drill:
- Impeller blades.
- Thin-walled parts of the rotor casing.
- Zones near the bearing seats or splined joints.
Method 3: fitting removable weights (bolts, clamps)
This method is convenient for quick correction and where welding is not permissible.
When to use it:
- On rotors that have dedicated threaded holes for balancing bolts.
- On car wheel rims (balancing clip-on weights).
- When frequent re-balancing is needed.
Important points:
- Use high-strength fasteners (grade 8.8 and above).
- Always use washers or thread-locking compound (such as Loctite) to prevent the fastener from working loose under vibration.
Work safety
Working with correction weights demands strict adherence to safety procedures.
- All work to fit and remove weights is carried out only on equipment that is fully stopped and isolated (the LOTO procedure).
- When welding, observe all fire-prevention precautions.
- After fitting a weight, make sure it does not catch on any stationary parts of the casing.
Professional balancing
Our specialists will choose the optimum correction method for your equipment.
Quick checklist
- Weld steel plates fully round on steel/cast-iron rotors
- Clean weld areas down to bare metal
- Drill only bosses, disc faces or ribs
- Use grade 8.8+ fasteners with thread-lock for bolts
- Work only on stopped, isolated equipment (LOTO)
- Check fitted weight clears stationary casing parts