Repair of splined joints

Repair of Keyways and Splines

Malfunctions of keyways and splines can manifest as wear and deformation of their surfaces, or chipping of metal on working surfaces.

When repairing worn key joints, the damaged key is replaced with a new one of normal or increased size.

Therefore, the repair of keyways on a shaft is recommended to be carried out by:

• widening the worn keyway (by 10-15%) for an oversized key;
• milling a keyway for a normal-sized key in another location, shifted by 90 or 120° from the damaged keyway;
• surfacing the walls of worn keyways with subsequent milling to their normal size.

Worn shaft splines can be restored by:

• upsetting the splines;
• surfacing the worn side surfaces of the spline teeth;
• continuous surfacing of spline roots and tooth surfaces.

Repair of Splined Connections

Splines of small shafts are usually not repaired; parts with worn splines are mostly replaced with new ones. However, for parts that are labor-intensive to manufacture, splines are often repaired. This is done by welding metal with subsequent machining in precise accordance with the dimensions and location of the splines on the part.

Regardless of the repair method, the final spline size is obtained by machining to nominal or oversized dimensions, which allows for compensating for spline wear in the mating bore.

Stages of Spline Repair at MB Master Car Service

• When repairing splines by upsetting, they are annealed. Upsetting is performed manually or on presses using special tools – chisels and mallets. For this, one longitudinal scratch is applied along the splines, then grooves are cut along the scratches with a chisel, which are then upset with a chasing hammer.
• Spline upsetting can be performed using lathes or planing machines. For this, a mandrel with a rotating conical roller is clamped in the tool holder of the machine, and the shaft is installed in the centers of the lathe or clamped on the table of the planing machine. The machine’s carriage advances the roller, presses it into the tooth body, and makes several passes along one groove. As a result, the width of the splines increases by 0.5-1 mm.
• Depending on the amount of wear, spline upsetting is performed along the edge of the worn surface or along both edges of the tooth.
• The grooves formed on the splines are filled by electric welding and cleaned, and the splines themselves are fitted to the mating part by machining.
• After surfacing, the shaft is turned to the specified size, the overlays are trimmed from the end, and a chamfer is made.
• Splines are machined on gear hobbing machines with hob cutters or on horizontal milling machines with disc or form cutters.

Shaft splines can be repaired by upsetting the teeth when the spline connection is centered on the inner diameter.

Repair of Keyed Connections

Keyed connections serve to transmit torque from a shaft to the hub of a transmission element (gear, pulley, half-coupling, etc.) or vice versa, from the hub to the shaft. In addition to torque transmission, keys can fix hubs mounted on the shaft in the axial direction.

When assembling and repairing keyed connections, keys must be precisely scraped to the dimensions of the keyways. Installing keys with sharp corners (without chamfers) is unacceptable. Chamfers should be 0.5-1 mm larger than the radius of the fillet in the keyway. The absence of fillets in keyways sharply reduces the fatigue strength of the shaft, and the absence of chamfers on keys can cause jamming in the corners of the keyways, preventing the key from seating properly.