Grinding

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

Overview

Grinding is a precision machining process that uses bonded abrasive wheels to remove very small amounts of material. It excels at holding tight tolerances, producing flat or round geometry, and achieving fine surface finishes, especially on hardened steels and difficult-to-machine alloys. Common sub-processes include surface grinding for flats, ID/OD grinding for bores and shafts, and centerless grinding for high-throughput cylindrical parts.

Use grinding when you need high dimensional accuracy, controlled geometry, and low Ra finishes after heat treat or prior machining. It is ideal for bearing fits, sealing surfaces, tooling, and gages where runout, roundness, and flatness really matter. Tradeoffs: slower material removal, higher part cost than rough machining, and tighter setup constraints. It works best as a finishing step on pre-machined parts, not as a stock-removal method from raw bar or plate.

Common Materials

  • Hardened tool steel
  • Stainless steel 17-4
  • Stainless steel 440C
  • Carbide
  • Inconel 718
  • Aluminum 6061

Tolerances

±0.0002" to ±0.0005"

Applications

  • Shaft journals and bearing seats
  • Hydraulic spools and valve components
  • Precision punches, dies, and molds
  • Flat tooling plates and parallels
  • Gage blocks and precision spacers
  • Hardened bushings and ID bearing bores

When to Choose Grinding

Choose grinding when you need very tight tolerances, controlled flatness/roundness, or fine surface finish, especially on hardened or heat-treated parts. It fits best as a finishing operation on pre-machined components at low to medium volumes. Use it where functional fits, sealing surfaces, or gaging surfaces drive performance or assembly yield.

vs Milling

Pick grinding instead of milling when tolerance, flatness, or surface finish requirements exceed what a typical CNC mill can hold economically, especially after heat treat. Use grinding to clean up distortion, improve parallelism, and hit precision fits on critical faces or slots.

vs Turning

Choose grinding over turning when cylindrical parts need extremely tight OD/ID tolerances, low runout, or fine finishes on hardened shafts and bores. Grinding is ideal once the part is heat-treated and turned near-net, then finished to final size and geometry.

vs Drilling

Use grinding rather than drilling when hole size, roundness, or surface finish need refinement beyond what standard drills and reamers can achieve. ID grinding is suited for hardened bores, bearing fits, and tight clearance holes that must stay accurate after heat treatment.

vs Electrical Discharge Machining (EDM)

Select grinding over EDM when the geometry is simple (flats, rounds) and you want higher throughput, lower cost per part, and no recast layer. Grinding is better for cleaning up EDM’d surfaces to improve finish and tolerance on sealing or sliding interfaces.

vs Broaching

Choose grinding instead of broaching for lower volumes, frequent design changes, or when features need tighter size control or finish than a standard broach provides. It avoids custom tooling costs and can fine-tune critical faces or diameters after broaching if needed.

Design Considerations

  • Leave a consistent grinding allowance, typically 0.003"–0.010" per surface, so the shop can clean up distortion and tool marks without chasing size
  • Clearly identify datum surfaces and which faces or diameters require grinding versus standard machining to avoid unnecessary cost
  • Specify surface finish and tight tolerances only on functional areas; relax non-critical surfaces to keep cycle times and prices down
  • Avoid very deep, narrow slots or sharp internal corners where grinding wheel access is limited; include realistic corner radii that match standard wheel shapes
  • Call out roundness, flatness, and runout requirements where functionally needed so the grinder can fixture and inspect correctly
  • Select materials and heat treatments compatible with grinding to reduce wheel loading and burning, and share hardness targets on the print