Grinding

Grinding removes small amounts of material with an abrasive wheel to achieve very tight tolerances, fine finishes, and accurate geometry on hard materials.

Overview

Grinding is a precision machining process that uses abrasive wheels to size and finish parts. Common sub-processes include surface grinding for flats, OD/ID grinding for external/internal diameters, and centerless grinding for high-throughput cylindrical parts without centers.

Choose grinding when dimensions, roundness/flatness, or surface finish are function-critical—especially after heat treat. It’s often the last operation to hit final size on hardened steels, tool steels, and wear alloys.

Tradeoffs: grinding is slower per cubic inch removed than cutting processes and typically isn’t economical for heavy stock removal or nonfunctional surfaces. Wheel selection, dressing, and workholding drive results; poor thermal control can cause burns, microcracks, or distortion. Expect higher cost when tolerances are tight, parts are thin/heat-sensitive, or inspection requirements are rigorous.

Common Materials

  • 4140 steel
  • D2 tool steel
  • 52100 bearing steel
  • 17-4 PH stainless
  • Inconel 718
  • Aluminum 6061

Tolerances

±0.0002" to ±0.001"

Applications

  • Bearing journals and races
  • Hardened gearbox shafts
  • Valve spools and hydraulic pistons
  • Precision ground gauge blocks and parallels
  • Die and mold shutoff surfaces
  • Centerless-ground dowel pins

When to Choose Grinding

Pick grinding for features that must hold tight size, form, and finish—typically critical flats and precision diameters. It fits low to medium volumes for high-accuracy parts and high volumes for centerless cylindrical work. It’s a strong choice when parts are hardened or when final geometry needs correction after heat treat.

vs Milling

Choose grinding when flatness/parallelism and surface finish are function-critical, or when the material is hardened and milling tool wear becomes a problem. Grinding is often the go-to for final sizing after milling leaves a small stock allowance.

vs Turning

Choose grinding when OD/ID diameters need better size control, roundness, or finish than a turned surface can reliably hold—especially on hardened shafts and bores. Grinding also helps correct slight distortion after heat treat that turning may simply follow.

vs Drilling

Choose grinding when hole geometry and finish requirements exceed drilled capability, such as tight ID size, taper control, or fine finish in hardened material. ID grinding is typically used after a hole is roughed (drilled/boring/reamed) to reach final size and form.

vs Electrical Discharge Machining (EDM)

Choose grinding when you need superior surface finish, better throughput on accessible surfaces, or when recast layers are not acceptable. Grinding also works well for long, straight flats and diameters where wheel access is simple and repeatability is key.

vs Broaching

Choose grinding for low-to-medium volumes, hardened parts, or when you need flexible geometry changes without dedicated tooling. Grinding is better suited for finishing critical surfaces around formed features after broaching or heat treat.

Design Considerations

  • Specify the functional surfaces to grind and leave other faces as-machined to avoid unnecessary time and cost
  • Leave a realistic grind stock allowance (commonly 0.0005–0.010 in depending on size and heat treat distortion risk) and call it out on the drawing
  • Avoid thin walls and interrupted grinding where possible; they increase chatter, burn risk, and cycle time
  • Provide clear datums and inspection requirements for form (flatness, roundness, cylindricity) so the shop can plan setups and gaging
  • Add reliefs/undercuts near shoulders on ground diameters to give wheel clearance and prevent corner rub
  • Call out surface finish only where needed; very low Ra requirements drive wheel choice, dressing frequency, and cost