Centerless Grinding

Centerless grinding finishes external cylindrical surfaces with high throughput, tight diameters, and excellent roundness without using centers or chucks.

Overview

Centerless grinding is a high-precision process for finishing external cylindrical surfaces without holding the part between centers. The workpiece is supported by a work rest blade and ground between a grinding wheel and a regulating wheel. Thru-feed centerless grinding excels at simple, straight cylindrical parts, while infeed (plunge) centerless grinding handles parts with shoulders, steps, and short features.

Use centerless grinding when you need tight diameter control, superior roundness, and smooth surface finishes on pins, shafts, and rods at medium to high volumes. It offers fast cycle times, minimal loading/unloading time, and strong process repeatability. Tradeoffs: it is limited mainly to round external geometries, needs stable blanks with reasonable straightness, and requires some setup development for optimum results. Features too close to shoulders, large interruptions, or complex non-cylindrical geometry may require other grinding or turning methods.

Common Materials

  • Aluminum 6061
  • Stainless Steel 303
  • Stainless Steel 17-4
  • Alloy Steel 4140
  • Tool Steel A2
  • Tungsten Carbide

Tolerances

±0.0002" on diameter, ≤0.0001" roundness

Applications

  • Dowel pins and locating pins
  • Hydraulic and pneumatic shafts
  • Automotive valve stems and piston pins
  • Bearing and bushing outer diameters
  • Medical guidewires and pins
  • Precision pump and motor shafts

When to Choose Centerless Grinding

Choose centerless grinding for straight or shouldered cylindrical parts where diameter, roundness, and surface finish are critical, especially at medium to high production volumes. It is ideal when you can present the part as a simple OD to be ground, with enough length to be supported on a work rest blade. It works best when blanks are reasonably straight and you need stable, repeatable size control across many parts.

vs Surface Grinding

Pick centerless grinding over surface grinding when your critical feature is an external cylindrical diameter rather than a flat. Centerless will hold tighter roundness and size on shafts and pins and run much faster for bar-like parts, while surface grinding is better for flat faces, plates, and prismatic geometry.

vs ID Grinding

Choose centerless grinding instead of ID grinding when the outer diameter is the controlling feature or datum and the part is essentially a solid or tube-like shaft. Centerless offers higher throughput and lower cost for OD control, while ID grinding is reserved for tight-tolerance bores or internal features.

vs OD Grinding

Use centerless grinding instead of between-centers OD grinding when you have many similar cylindrical parts and want faster production without chucking or centers. Centerless generally gives better throughput and can be more stable for small-diameter or slender shafts prone to deflection in traditional OD setups.

vs CNC Turning

Select centerless grinding over CNC turning when you need tighter diameter and roundness than turning normally achieves, or when surface finish and consistency over large quantities are critical. Turning is efficient for creating the initial geometry and features, but centerless grinding is better for final sizing and finishing of critical ODs.

Design Considerations

  • Keep critical centerless-ground sections cylindrical and continuous; avoid deep keyways, large flats, or slots interrupting the grinding zone
  • Maintain adequate distance between shoulders and the ground diameter to allow wheel and work rest access, typically at least one wheel width
  • Specify realistic grind stock (commonly 0.002"–0.010" per side) and ensure incoming blanks are straight enough to clean up
  • Group diameters that will be thru-fed to the same or compatible sizes to reduce setups and tooling changes
  • Call out clear datums, diameter tolerances, and roundness requirements so the shop can choose appropriate infeed or thru-feed setups
  • If chamfers or lead-ins are required on ground diameters, dimension them explicitly and keep them modest so parts can still track properly through the machine