Type 27 vs. Type 29 Flap Discs: Differences, Uses & Grinding Angles
Type 27 and Type 29 flap discs use the same basic idea—overlapping abrasive flaps on a backing plate—but their shapes create different contact patterns on the workpiece. A Type 27 flap disc is flat. A Type 29 flap disc is conical. That difference changes the working angle, pressure concentration and tasks each shape handles best.
This guide compares Type 27 vs. Type 29 flap discs for weld grinding, blending, deburring, edges and surface preparation, then helps you choose the right zirconia disc and grit.
Quick decision
Choose Type 27 for flatter work, broad contact, controlled blending and a shallower grinder angle.
Choose Type 29 when a steeper working angle and concentrated contact are useful for stock removal, welds, edges, contours or bevel work.
Type 27 vs. Type 29 flap discs at a glance
| Feature | Type 27 | Type 29 |
|---|---|---|
| Profile | Flat | Conical or angled |
| Recommended working angle | Approximately 0–15° | Approximately 15–25° |
| Contact pattern | Broader contact at a shallow angle | More concentrated contact at a steeper angle |
| Best starting point | Flat surfaces, blending, finishing and controlled weld cleanup | Faster stock removal, weld grinding, contours, edges and beveling |
| Operator feel | More forgiving when kept shallow | Responds well to purposeful pressure and angle |
| Common mistake | Using it perfectly flat or raising the angle too far | Using it too shallow, on the edge, or jamming it into a tight corner |
3M identifies Type 27 as the flat form and Type 29 as the conical form. Norton recommends working Type 27 flap discs at about 0–15° and Type 29 discs at about 15–25°. Always follow the angle, RPM and safety information printed on the specific disc and supplied by its manufacturer. See the official 3M flap-disc overview and Norton flap-disc safety guidance.
What makes Type 27 different?
The flat Type 27 profile brings more of the flap surface into contact when the grinder is held at a shallow angle. That makes it a practical choice when the goal is to blend a weld into a broad flat panel without concentrating all the pressure into a narrow band.
Good Type 27 starting applications
- Weld blending on flat plate
- Surface preparation before coating
- Removing mill scale or oxidation from broad areas
- Smoothing scratches and previous grinding marks
- Controlled finishing where gouging must be minimized
Type 27 watch-outs
- Do not run it on the thin edge of the disc
- Do not assume “flat” means zero angle in every situation
- A steep angle concentrates wear on a small flap area
- Too little effective pressure can generate heat and cause loading
What makes Type 29 different?
The conical Type 29 profile is designed to work at a steeper angle. Its geometry places a more concentrated area of abrasive against the work, which can improve control during heavier weld removal, edge preparation and contour work.
Good Type 29 starting applications
- Removing raised weld beads
- Stock removal on steel and stainless steel
- Bevel preparation
- Deburring edges
- Working on curved or contoured surfaces
Type 29 watch-outs
- It is not automatically better for every weld
- Excess pressure can remove more material than intended
- A shallow angle may prevent the conical profile from working correctly
- Jabbing the disc into a tight corner can damage the flaps
Which flap disc should you use for common jobs?
| Job | Recommended starting shape | Why |
|---|---|---|
| Blend a weld flush on flat sheet | Type 27 | Broad contact helps smooth the transition across the panel |
| Remove a heavy raised weld | Type 29 | Conical profile concentrates the working area at a steeper angle |
| Prepare a bevel | Type 29 | Steeper geometry is easier to direct along the edge |
| General surface preparation | Type 27 | Controlled contact over flatter areas |
| Deburr a cut edge | Type 29, with control | Concentrated contact can reach the edge without laying the grinder flat |
| Blend a curved or contoured part | Type 29 or a more conformable finishing abrasive | Shape can follow the contour more naturally, but the material and finish target matter |
| Fine cosmetic finishing | Type 27 with finer grit | Broader contact and finer grit reduce deep scratch concentration |
If both shapes can perform the job, base the decision on the finish requirement and how the operator naturally holds the grinder. A Type 29 disc used too shallow or a Type 27 disc used too steeply can wear prematurely and produce inconsistent results.
Flap-disc grit selection
Shape and grit solve different problems. Shape determines contact geometry; grit determines the aggressiveness of each abrasive flap.
| Grit | Practical starting use | Finish expectation |
|---|---|---|
| 36 grit | Heavy weld and stock removal | Fast cut with deep scratch pattern |
| 40 grit | General heavy grinding and weld cleanup | Aggressive but slightly more controlled than 36 |
| 60 grit | General-purpose grinding and blending | Balanced removal and finish |
| 80 grit | Blending, deburring and surface preparation | Finer and easier to refine |
| 120 grit | Light finishing and scratch refinement | Fine finish with limited stock removal |
A common shop sequence is to remove the weld with a coarse disc and then step to a finer grit only when the finish requires it. Skipping too many grit steps can leave coarse scratches visible beneath the final finish.
Standard vs. premium zirconia flap discs
Zirconia abrasive is a strong choice for steel and stainless-steel fabrication because the grain fractures during use and exposes new cutting edges. Disc construction, flap density, backing rigidity and abrasive quality still affect how consistently that self-sharpening action occurs.
- Standard zirconia Type 27: a value-focused choice for general grinding, weld blending and surface preparation.
- Premium zirconia Type 27: suited to production grinding where a flat profile and more demanding duty are required.
- Premium zirconia Type 29: built for the conical contact pattern used in higher-pressure stock removal and weld grinding.
Recommended flap discs
Standard Zirconia Type 27
Flat 4-1/2 × 7/8 in flap discs for general steel and stainless-steel grinding, blending and preparation.
View Standard Type 27 →
Premium Zirconia Type 27
A flat premium option for production weld blending and broad surface preparation.
View Premium Type 27 →
Premium Zirconia Type 29
Conical construction for steeper-angle grinding, concentrated contact and efficient stock removal.
View Premium Type 29 →Flap-disc safety checklist
Flap discs are high-speed abrasives. Shape selection does not replace safe mounting and operation.
- Use the grinder guard and side handle supplied for the tool.
- Wear appropriate eye, face, hearing, hand, body and respiratory protection for the material.
- Disconnect power before installing or changing the disc.
- Confirm the disc diameter and arbor match the grinder.
- Never exceed the maximum RPM printed on the disc.
- Inspect the backing and flaps before use; discard a dropped or damaged disc.
- Keep bystanders and flammable materials clear of the debris and spark path.
- Do not use a flap disc on its edge or jam it into a tight location.
- Follow the abrasive and grinder manufacturers' instructions and applicable workplace procedures.
Norton notes that incorrect angle or surface use can damage the backing or cause flap separation, and that guards are required on machines designed to use them. Review the full flap-disc safety refresher before operation.
Type 27 vs. Type 29 FAQ
Is Type 29 always more aggressive than Type 27?
No. The conical profile concentrates contact and is often selected for heavier removal, but actual cut rate depends on grit, abrasive grain, backing, pressure, grinder speed and material.
Can Type 27 remove welds?
Yes. Type 27 is especially useful when the weld must be blended into a flat surrounding surface. Type 29 is often preferred when the first priority is concentrated stock removal.
Can I use a Type 29 disc flat?
No. Use the working-angle range stated by the manufacturer. Norton recommends approximately 15–25° for Type 29 flap discs.
Which grit is best for weld removal?
Start with 36 or 40 grit for heavier removal, then use 60 or 80 when more control or a finer blended finish is required. Test on scrap when finish requirements are critical.
Can the same flap disc be used on steel and stainless steel?
Only when the disc is specified for both materials. Avoid cross-contaminating stainless steel with a disc previously used on carbon steel when corrosion resistance or appearance matters.
Not sure which flap disc fits the job?
Send the metal, weld or edge condition, grinder size, desired finish, current grit and expected usage. The recommendation form sends the details to our CRM for review.
For more technical product-selection articles, visit the Machinist's Vault Education hub or browse the latest blog and news guides.
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Reviewed By
This guide is reviewed by Kartar Chalotra, who leads sales and operations at Rise Tek Machinery.