DeWalt High Density Flap Disc - Type 27

Why this flap disc has become a regular in my grinder kit

On any given week I’m blending welds, knocking back mill scale, and prepping edges on mild steel and stainless. I’ve been running DeWalt’s high-density Type 27 flap disc as my go-to for flat grinding and blending, and it has been a steady, predictable performer with fewer surprises than most of the discs I’ve cycled through.

This disc uses a ceramic/zirconia-alumina abrasive on a high-density flap stack. In practice, that combination hits two big targets: it holds a fast cut under real pressure and it lasts appreciably longer than standard zirconia-only discs. I ran it primarily in 4-1/2 and 5-inch sizes on angle grinders rated 10,000–12,000 RPM, and I also tested a 7/8-inch arbor version and a 5/8-11 threaded hub for quick swaps.

Setup and compatibility

• Type: 27 (depressed center), intended for flat grinding and shallow angles.
• Sizes tested: 4-1/2 and 5 inch. The line also includes 6 and 7 inch, with a 13,300 RPM max across the family.
• Arbor: I like the 5/8-11 threaded hub for convenience; the 7/8-inch bore works fine with a standard flange.
• Grits used: 40 and 60 for removal; 80 for finishing passes. The series also goes to 120 if you need a finer scratch.

If you’re used to Type 29 (conical) discs for aggressive stock removal at a steeper angle, note that this Type 27 runs flatter and rewards a 0–15 degree approach. For flush weld blending on plate and tube, it’s the right geometry.

Cutting performance

I benchmark flap discs by timing a few common jobs:

• Flattening a 3/16-inch fillet weld on mild steel angle, then blending the toe into base metal.
• Removing heavy scale from hot-rolled flat bar.
• Chamfering 1/8-inch edges for weld prep.
• Smoothing TIG welds on 304 stainless without over-bluing the surrounding area.

With a 40-grit disc and moderate-to-firm pressure, this one takes the crown off a MIG bead quickly and stays cutting without the “skating” feeling you get when an abrasive dulls. It doesn’t quite match a hard grinding wheel for raw aggression on a big, proud weld, but it’s closer than most flap discs I’ve used—close enough that I rarely feel the need to switch to a wheel unless I’m hogging out a heavy section or needing a deep notch.

Where it shines is control. With the grinder nearly flat, I can feather into the parent metal without digging gouges. The scratch pattern is consistent and easy to chase with 60 or 80 grit. Blend lines are minimal, and I can go directly to a conditioning disc or a flap wheel if I’m aiming for a brushed cosmetic finish.

On stainless, 60 and 80 grits cut briskly and run relatively cool for a ceramic/zirconia disc as long as I keep the pressure steady and avoid lingering in one spot. Light pressure can cause ceramic grains to “glaze” on some discs; this one responds better when you lean into it a bit, which helps the ceramic grain micro-fracture and self-sharpen. If I back off too much, removal slows.

Finish quality and heat control

Compared to a fiber disc, the finish is similar but more controlled around edges and radii. I see a uniform scratch that’s easy to clean up. The disc does throw a healthy stream of sparks—about what you’d expect for a ceramic/zirconia product—and heat tint on stainless stays manageable with a steady pass. As with any flap disc, you can still overheat thin sections if you park the wheel; keep it moving.

One nice trait: the high-density pack helps the disc “float” slightly over uneven surfaces. That makes it forgiving when feathering thin stock or blending across a weld crown into base metal.

Life and wear pattern

High-density flap discs carry more abrasive, and the payoff here is obvious. In back-to-back jobs, I consistently got roughly double the working life compared to mid-grade zirconia flaps I keep on hand. After a long weld-blending session, flaps remained intact with no premature shedding. The disc wears evenly, and the cut stays predictable deep into the disc’s lifespan.

If you’re price-sensitive, the upfront cost is higher than a standard flap disc. However, the throughput per disc—plus fewer swaps mid-job—balances that out for me. On labor-heavy tasks, it’s worth it.

Ergonomics and feel

• Balance: Runs true with minimal chatter. Even at high RPM, it stays smooth.
• Vibration: Low. The dense pack damps some vibration versus thinner discs.
• Control: Excellent for flat work and edge chamfering. The depressed center helps keep the grinder’s hardware off the work for flush blending.
• Noise: Typical for a flap disc; less “harsh” than a hard wheel.

If you’ve ever fought a flappy, unbalanced disc that chatters and leaves scallops, this is the opposite experience—confident, steady, and predictable.

Where it excels

• Weld blending on plate and tube where a flush finish is the goal.
• Removing weld slag and heavy scale without swapping to a hard wheel.
• Edge blending and breaking sharp corners ahead of paint or powder.
• Stainless work where you want a quick cut and a manageable heat-affected zone.

For shop productivity, the fact that it can run near grinding-wheel removal rates but leave a fiber-disc-like finish means fewer tool changes and faster progress to your next finishing step.

Limitations and considerations

• Tight spaces: The high-density pack is thick. In tight corners, inside fillets, or around obstructions, it can feel bulky. A thinner disc or a smaller diameter may be better there.
• Geometry: Type 27 prefers a flatter approach. If you like grinding at a steep angle or need aggressive edge work, a Type 29 may suit you better.
• Nonferrous metals: Like most ceramic/zirconia flaps without a dedicated grinding aid, it can load on aluminum and softer alloys. If you must use it there, keep it clean and consider a wax stick, but I’d reach for a disc formulated for nonferrous instead.
• Pressure matters: The ceramic really wakes up under firm pressure. Too light and the cut slows. That’s normal, but worth noting if you’re used to “floating” a standard zirconia.

Grit and technique tips

• 40 grit: Fast stock removal, weld knockdown, heavy scale. Maintain 5–10 degrees on steel; keep it moving.
• 60 grit: Blend after the 40, or run it as your first step if the weld is already close to flush.
• 80–120 grit: Refining passes, prep for coatings, light cosmetic blending. On stainless, alternate pass directions to even out the scratch.
• Pressure: Moderate to firm keeps the ceramic sharp. If you feel the disc skating, add a touch more pressure.
• Speed: Stay within the disc’s 13,300 RPM max. Most 4-1/2 and 5-inch grinders are fine; don’t overspeed larger diameters.
• Safety: Use a guard, gloves, eye and ear protection, and watch your grinding angle to avoid kick or edge-catch.

Durability, value, and availability

Between the long-lasting high-density pack and the consistent cut, the disc makes a strong case on cost-per-use. I also like that it’s available in the common diameters with both 7/8-inch and 5/8-11 hubs, so outfitting multiple grinders is straightforward. Pack quantities vary, but boxes of five are a good sweet spot for general shop work without tying up too much shelf space.

Who it’s for

• Fabricators and welders who prioritize clean, flat blends on steel and stainless.
• Maintenance crews that want one disc that can remove material fast and still leave a finish that’s easy to coat.
• DIYers who’d rather buy fewer, better discs than churn through low-cost flaps mid-project.

If your work leans heavily into inside corners, tight jigs, or nonferrous, supplement with thinner discs or non-loading formulations. Otherwise, this flap disc will cover most of your grinding and blending needs.

Recommendation

I recommend this DeWalt flap disc for anyone doing regular weld blending, surface prep, and edge work on steel and stainless. It cuts fast under real pressure, leaves a controllable and consistent finish, and, importantly, it lasts—often two times longer than standard zirconia flaps in my tasks. The Type 27 geometry makes flush blending straightforward, and the balance and feel reduce chatter and rework. Factor in fewer changeovers and cleaner blends, and it’s a solid value for both shop and field use.