How to Choose the Right Grit for Aluminum Oxide Lapping Discs

By Supergrit Abrasives | Published: 2026-10-23

Category: How-to Guides

Learn how to select the right grit for aluminum oxide lapping discs, from coarse to fine, for precision lapping and smooth finishes.

Quick Answer

Choose a finer grit like 12 MIC for finishing and polishing, while coarser grits are better for rapid stock removal. Match the grit to your surface finish and material removal needs.

Understand Grit Numbers vs. Micron Ratings

Lapping discs use either conventional grit numbers (e.g., 120, 400) or micron ratings (e.g., 12 MIC). Micron ratings indicate the average particle size in micrometers, with smaller numbers meaning finer abrasives. For precision lapping, micron-rated discs often provide more consistent finishes than grit-numbered equivalents.

Match Grit to Material and Finish

Softer metals like aluminum may require coarser grits to avoid clogging, while harder steels benefit from finer grits for a mirror finish. Always consider the surface roughness you need: coarser grits remove material faster but leave deeper scratches, while finer grits refine the surface but are slower.

Consider the Lapping Process

Lapping is a controlled abrasive process that flattens surfaces and achieves tight tolerances. The grit choice affects not only the finish but also the flatness and dimensional accuracy. For multi-step lapping, start with a coarser grit to establish flatness, then progress to finer grits to refine the surface.

Step-by-Step Grit Selection Guide

Assess Your Surface Finish Requirements: Determine the desired surface roughness (Ra) for your workpiece. For a mirror finish, choose a finer grit like 12 MIC; for a matte finish, a coarser grit may suffice. Check your specifications for the required Ra value before selecting a grit.
Evaluate Material Removal Needs: If you need to remove significant material or correct flatness, start with a coarser grit (e.g., 60-120) to speed up the process. For light stock removal and finishing, skip to finer grits. Avoid starting with too fine a grit if you have deep scratches or uneven surfaces.
Consider the Workpiece Material: Softer materials like aluminum may load the abrasive quickly; use a coarser grit or a stearated disc to reduce clogging. Harder materials like steel require finer grits for efficient polishing. Test on a scrap piece to see how the disc behaves on your specific material.
Plan a Multi-Step Lapping Sequence: For best results, use a progression: start with a coarse grit to establish flatness, then move to medium (e.g., 30-60 MIC) and finally a fine grit like 12 MIC for the final finish. Always clean the workpiece between grit steps to avoid contamination.
Check Disc Compatibility and Size: Ensure the disc size (e.g., 9") matches your lapping machine or backup pad. Also verify the backing (solid plain back) is suitable for your process. Confirm the disc's dimensions and backing type before purchasing.

Product Facts

SOLID PLAIN BACK 3M YELLOW (IMPERIAL FILM) AO LAPPING DISCS: These 3M Yellow (Imperial Film) AO lapping discs are solid plain-back discs in 12 MIC grit, available in 9" dimensions. The 12 MIC grit is ideal for final finishing and polishing steps in precision lapping, delivering a smooth, consistent surface.
SOLID PLAIN BACK 3M YELLOW (IMPERIAL FILM) AO LAPPING DISCS