Type 27 Flap Disc on Stainless: Grit and Speed Basics

By Supergrit Abrasives | Published: 2026-11-02

Category: How-to Guides

Learn how to run a Type 27 flap disc on stainless steel without heat damage. Covers grit choice, grinder speed, and a step-by-step finishing sequence.

Quick answer

For stainless steel, start with a coarser grit to remove weld or scratches, then finish with 100 grit or finer. Keep your angle grinder at or below the disc's rated RPM and use light pressure to avoid heat tint.

Why stainless steel punishes heat and contamination

Stainless steel work-hardens and discolors when it gets too hot. A flap disc that runs too fast or with too much pressure can leave a blue or brown tint that is difficult to remove. Contamination from carbon steel dust is another risk: keep stainless parts separate from regular steel work and clean the grinder and disc before switching materials.

Match grit to the job, not to the disc color

A flap disc grit for stainless should be chosen by the surface you start with. Use 40–60 grit for heavy weld removal, 80 grit for blending, and 100 grit or finer for finishing. Jumping straight to a fine grit on a rough weld wastes discs and can overheat the surface.

Speed limits and grinder compatibility

Check the maximum RPM printed on the disc and never exceed it. A 7-inch disc needs a grinder rated for that size; using a larger disc on a small grinder can overspeed the disc and is unsafe. For a flat flap disc on an angle grinder, a typical no-load speed of 8,000–11,000 RPM is common, but always follow the disc's rating.

Step-by-step stainless finishing with a Type 27 flap disc

Inspect and clean the surface: Remove all oil, paint, and carbon steel contamination from the stainless part. Use a dedicated stainless wire brush or solvent, and keep the area clean before grinding. Skipping this step can embed contaminants that cause rust later.
Mount the disc and set the guard: Fit the 7-inch flat flap disc on a grinder rated for 7-inch wheels. Adjust the guard to protect you from sparks and debris, and check that the disc spins freely. Never run a 7-inch disc on a smaller grinder; the RPM rating must match.
Start with a coarser grit for stock removal: Use 40–60 grit to remove welds or deep scratches. Hold the grinder at a 5–10 degree angle to the work and use light, steady pressure. Keep the disc moving to avoid heat buildup. A common mistake is pressing hard and dwelling in one spot, which causes heat tint.
Blend with 80 grit: Switch to an 80-grit flap disc to smooth the scratches left by the coarser grit. Overlap your passes by about 50% and maintain the same low angle. Skipping intermediate grits makes the final finish uneven and takes longer.
Finish with 100 grit or finer: For a bright, uniform finish, use a 100-grit disc like the Supergrit Abrasives 7" X 5/8"-11 Type 27 flat flap disc. Reduce pressure further and keep the grinder moving in long, consistent strokes. If you see heat tint, stop and let the part cool; do not try to grind it away with more pressure.
Clean and passivate if needed: After grinding, wipe the surface with a clean cloth and remove all dust. For critical stainless applications, apply a passivating solution according to the manufacturer's instructions. Leaving grinding dust on the surface can lead to contamination and rust spots.

Product facts

7" X 5/8"-11 FLAP DISC TYPE 27 (FLAT) - HD USA 100 GRIT: 7-inch Type 27 (flat) flap disc with 5/8"-11 arbor hole, 100 grit, HD USA. The 100 grit is a finishing choice for stainless steel, and the 7-inch size suits large flat areas where a flat disc maintains contact.
7" X 5/8"-11 FLAP DISC TYPE 27 (FLAT) - HD USA 100 GRIT