T27 and T29: The Two Flap Disc Shapes
Flap discs are classified by their profile shape, designated by type numbers: T27 (depressed center, flat profile) and T29 (depressed center, conical/convex profile). The shape determines the grinding angle and optimal contact pattern with the workpiece.
T27 Flap Disc: The Flat Profile
What It Looks Like
T27 flap discs have a flat profile with a slight depression at the center where they mount to the grinder. The abrasive flaps lay relatively flat, presenting a 0-15° grinding angle.
Best Applications
- Flat surface grinding: Smoothing and leveling flat metal surfaces
- Blending and finishing: Creating uniform surface finishes
- Working at shallow angles: 0-15° to the workpiece
- Stainless steel finishing: Controlled, flat contact
- General purpose grinding: The most versatile shape
Advantages
- Maximum contact area on flat surfaces
- Smooth, consistent finish
- Versatile for most applications
- Easier to control for beginners
T29 Flap Disc: The Conical Profile
What It Looks Like
T29 flap discs have a conical (angled) profile that flares outward from the center. The abrasive flaps are angled at approximately 15-30° from flat, creating a more aggressive cutting action.
Best Applications
- Aggressive stock removal: Fast material removal
- Edge work and chamfering: Grinding edges and corners
- Weld removal: Getting into corners and tight spaces
- High-angle grinding: 15-30° to the workpiece
- Contoured surfaces: Following curves and profiles
Advantages
- More aggressive cutting action
- Better access to edges and corners
- Flatter grinding angle for increased pressure
- Flaps wear more evenly on angled applications
T27 vs T29 Comparison
| Feature | T27 (Flat) | T29 (Conical) |
|---|---|---|
| Profile angle | 0-15° | 15-30° |
| Grinding angle | Shallow (0-15°) | Steeper (15-30°) |
| Material removal | Moderate | Aggressive |
| Surface finish | Smoother, more consistent | More aggressive texture |
| Edge access | Limited | Excellent |
| Flat surface work | Excellent | Good |
| Best for beginners | Yes | Less forgiving |
When to Use T27
Choose T27 flap discs when:
- Working primarily on flat surfaces
- Finish quality is important
- You're new to flap disc grinding
- Doing blending and surface preparation
- Working on stainless steel (reduces gouging)
When to Use T29
Choose T29 flap discs when:
- Maximum material removal is the priority
- Grinding edges, corners, or chamfers
- Removing welds in tight areas
- Working at higher grinding angles
- Following contoured or curved surfaces
Can You Use Both?
Many professional fabricators keep both T27 and T29 in stock:
- T29 40 grit: Aggressive weld removal and stock removal
- T27 60-80 grit: Blending, smoothing, and finishing
This combination covers the full range of grinding operations.
Conclusion: Match Shape to Application
Use T27 flat flap discs for controlled, smooth grinding on flat surfaces. Use T29 conical flap discs for aggressive stock removal, edge work, and corner access. Both have their place in a well-equipped shop.
At JKINGS Tools, we offer flap discs in both T27 and T29 profiles, across all grit sizes and grain types. Contact us for shape selection guidance.
