Case

Case Highlights

A European power tool brand supplying professional angle grinders and rotary hammers was seeing tooth breakage and high gear noise in heavy-duty use. Warranty returns on key models were higher than target, especially in construction and metal fabrication sites.

DD Gear redesigned the spur and helical gear train inside the gearhead using carburized alloy steels (20CrMnTi / 40Cr) and tighter ISO accuracy control. Similar materials and CNC processes are widely used for power-tool gears to ensure high strength and durability. After validation, the OEM recorded a clear drop in tooth-failure claims and perceived noise reduction at the operator’s ear, while keeping tool size and weight unchanged.

Customer Background & Project Scope

• Customer industry: EU manufacturer of professional-grade electric angle grinders, rotary hammers, and heavy-duty drills.

• Application: Gearsets in compact gearheads (typically spiral bevel + spur/helical combinations) transmitting high torque from a high-speed motor to the spindle. Spiral bevel and helical gears are common in angle grinders to handle high speed and improve smoothness.

• Project goals:

  • Increase tooth strength and fatigue life under abusive loads (binding discs, impact on rebar, etc.).

  • Reduce gear noise and vibration felt at the handle.

  • Maintain existing housing, spindle layout, and user ergonomics.

The OEM’s existing gears were sourced from a general machine supplier, using medium-carbon steel and conventional hardening. As the brand pushed for more power in the same housing, gear durability became the bottleneck.

Challenges

• Tooth breakage under overload

  • Field tools sent back from construction sites showed root cracks and broken teeth on pinions and bevel gears.

  • Failures often occurred after jam events (cut-off wheel stuck, hammer drilling in hard aggregate).

• Noise and vibration at the operator’s hand

  • At rated speed, tools produced noticeable gear whine and vibration, increasing fatigue during long shifts.

  • Spur stages and less precise machining contributed to impact and noise; spur gears are known to be noisier than helical gears because teeth engage suddenly.

• Volume & cost constraints

  • Any solution had to fit into a compact cast gearhead and remain competitive in cost, given high annual volumes.

DD Gear Solution

1. Gear Train Optimization

• Spiral bevel + helical/semi-helical layout

  • For angle grinders, DD Gear designed spiral bevel gears at the right-angle stage and helical or semi-helical gears in the parallel stage, similar to other high-performance grinder gearsets.

  • Helical teeth provide higher contact ratio and smoother engagement, which is widely recognized to reduce noise and vibration versus straight spur teeth.

• Tooth profile & root strength

  • Increased fillet radius and refined tooth thickness in critical gears to reduce stress concentration at the root.

  • Applied micro-geometry corrections (profile and lead modifications) so load is distributed more evenly along the tooth face, an approach commonly used to improve durability and lower noise.

2. Materials & Heat Treatment

• Carburizing alloy steels for key gears

  • Selected 20CrMnTi and 40Cr-class steels for pinions and high-loaded gears. These low-carbon alloy steels are widely used for gears because carburizing and quenching create a hard wear-resistant case with a tough core.

  • Case depth around 0.6–0.8 mm, tuned to module and load.

• Heat treatment & finishing

  • Carburizing + quenching + tempering, then gear shaving or grinding to reach the required flank accuracy and surface finish. Grinding is standard for high-precision hardened gears to control profile and avoid early failures.

  • Typical surface hardness HRC 58–60, with core toughness to absorb impact.

3. Manufacturing & Quality Control

• Small-module precision

  • Modules typically in the m 0.8–1.8 range, where tool wear and distortion must be closely controlled.

• Accuracy grade

  • Critical gears controlled to ISO 1328 Grade 6–7, aligning with typical accuracy requirements for compact industrial and tool gears.

• Process checks

  • CNC gear measuring machine used to sample tooth profile and lead deviations.

  • Periodic teardown of assembled gearheads to check contact pattern and backlash, based in part on existing best practices for small power-tool gearsets.

Results

After two rounds of prototypes and lab/field validation:

• Durability & claims

  • Warranty claims related to tooth breakage dropped noticeably on affected models after switch to DD Gear sets (internal data from the OEM’s service team).

  • In abuse tests (disc jam, heavy grinding on rebar), gears showed plastic deformation marks but no catastrophic tooth loss within the test window.

• Noise & vibration

  • Test operators reported less gear whine and smoother running, especially at no-load and partial-load speeds where customers are most sensitive.

  • This aligns with general findings that helical and spiral bevel gears, with gradual tooth engagement, reduce impact and noise compared with spur-only designs.

• Integration & cost

  • All improvements were achieved without enlarging the gearhead or changing the tool’s external form factor.

  • The OEM could keep existing housings and assembly lines, adjusting only gear suppliers and inspection plans.

Typical Technical Specifications

Representative values for a professional 125–150 mm angle grinder / rotary hammer platform.

Case Summary

By applying carburized alloy steels, optimized tooth geometry, and ISO-controlled accuracy, DD Gear helped this power-tool OEM:

• Reduce tooth breakage and warranty returns on high-torque tools.

• Improve noise and vibration behavior at the operator’s hand.

• Keep the same compact housing and external design, simplifying rollout.

This solution fits other professional electric tools such as cut-off saws, large drills, and demolition hammers that demand compact but tough gearsets.

Upgrading gears on your next angle grinder or rotary hammer platform?

Contact DD Gear’s engineers to co-develop hardened small-module gears tailored to your torque and NVH targets.