ID Grinding

ID grinding finishes internal diameters with abrasive wheels to achieve tight size, roundness, and surface finish on hardened or precision bores.

Overview

ID grinding (internal grinding) is a precision abrasive process for sizing and finishing bores. A grinding wheel runs inside the hole while the part rotates (or the wheel rotates around a stationary part), removing small amounts of material to hit final ID, roundness, and fine surface finish.

Choose ID grinding when a bore is tolerance-critical, needs excellent cylindricity, or is too hard for conventional boring/reaming. Common triggers are post-heat-treat sizing, bearing fits, hydraulic sealing surfaces, and concentricity to an OD or face.

Tradeoffs: it’s slower than cutting processes and needs rigid workholding, accurate datum control, and enough ID for wheel access. Deep bores, interrupted cuts, thin walls, and blind features raise risk of chatter, taper, and burn. Expect higher setup/inspection time, but predictable capability on challenging materials and tight geometry.

Common Materials

  • 4140 steel
  • 52100 steel
  • D2 tool steel
  • 17-4 PH stainless
  • Inconel 718
  • Aluminum 7075

Tolerances

±0.0002"

Applications

  • Bearing races and bearing housings
  • Hydraulic cylinder bores and gland bores
  • Gear bores and spline pilot bores
  • Precision bushings and sleeves
  • Tooling sleeves and hardened fixture bores
  • Valve bodies with critical internal seats

When to Choose ID Grinding

ID grinding fits low to medium volumes when a bore drives function and must meet tight size, roundness, and finish—especially after heat treat or coating. It’s a strong choice for parts needing controlled coaxiality between ID and OD with minimal material removal at final size.

vs Surface Grinding

Choose ID grinding when the critical feature is an internal diameter requiring roundness/cylindricity control. Surface grinding targets flatness and parallel faces; it won’t correct bore geometry beyond what the bore process already established.

vs OD Grinding

Choose ID grinding when the functional fit is inside the part (bearing seat, seal bore, bushing ID) or when the ID must be concentric to an existing datum. OD grinding controls external diameters well but does not directly improve internal geometry.

vs Centerless Grinding

Choose ID grinding when you need precision on an internal feature or tight relationship between an internal bore and datums. Centerless grinding is efficient for high-throughput external diameters on cylindrical parts, but it doesn’t address the bore and can’t establish ID-to-OD coaxiality by itself.

Design Considerations

  • Specify the functional datums (OD, face, pilot) that the ID must run true to, and call out TIR/cylindricity requirements explicitly
  • Provide adequate bore diameter and relief for wheel access; avoid sharp internal shoulders without a grind relief
  • Limit bore depth-to-diameter ratio when possible; deep, small IDs drive chatter risk, taper, and cycle time
  • Avoid interrupted bores (cross holes, keyways) in the grind zone or flag them early for wheel/parameter selection
  • Control wall thickness around the bore; thin sections distort under chucking and heat, hurting size and roundness
  • Define surface finish and any burn-sensitive requirements (hardness, microcrack limits) so the shop can plan feeds, coolant, and inspection