A depressed center grinding wheel has an offset mounting area that provides clearance around the flange and locking nut during compatible angle-grinding operations. Often called a raised-hub wheel or a depressed centre grinding disc, it is commonly used for weld removal, deburring, beveling and metal stock removal. Type 27 describes a common wheel shape; the label and manufacturer instructions determine the permitted application.
This guide explains the design, compares grinding and cutting wheel types, and helps you choose diameter, thickness, abrasive, grit and bond grade. FUJI has manufactured industrial abrasives since 1953, with different series serving everyday steel fabrication, stainless steel work and demanding foundry grinding.
The central mounting area sits below the surrounding face when viewed from the recessed side. This offset helps keep the mounting hardware clear of the workpiece when the wheel is used in its intended orientation. It does not automatically make every depressed-center disc suitable for side grinding, nor does it guarantee that the nut will be flush with every wheel and flange combination.
For grain, bond and pore structure, see our grinding wheel structure and marking guide.
Shape and permitted use must be checked together. In particular, a depressed-center cutting disc remains a cutting disc: a recessed center is not permission to apply side pressure.
| Wheel type | Typical form and task | Selection check |
|---|---|---|
| Type 27 grinding wheel | Depressed center; weld grinding, beveling and stock removal. | Use the working surface and angle specified for the actual wheel. |
| Type 29 grinding wheel | Angled grinding section on suitable bonded wheels, often for blending and controlled contact. | Check tool, guard and application compatibility. Type 29 also appears in flap-disc naming; the constructions differ. |
| Type 41 cutting wheel | Flat cutting wheel for cutting through the workpiece. | Do not side-grind with a cutting-only wheel. |
| Type 42 cutting wheel | Depressed-center cutting wheel. | The offset center does not make it a general-purpose grinding wheel. |
Some catalogues use Type 27/42 terminology for depressed-center cut-off products. Read the actual grinding/cutting designation, rather than relying on a shape number alone. Combination wheels must be explicitly approved for both tasks.
A bonded grinding wheel is a practical choice when substantial metal must be removed. A coated abrasive may be preferable when the surface finish or blending step matters more. Premium coated abrasives can also remove metal rapidly, so compare the complete task rather than assuming one construction always lasts longer or costs less.
| Abrasive tool | Typical reason to choose it | What to check |
|---|---|---|
| Depressed-center grinding wheel | Weld reduction, beveling and sustained stock removal. | Material compatibility, grade, heat control and remaining finishing work. |
| Flap disc | Blending grinding marks and combining removal with a more controlled finish. | Grit, abrasive material, disc shape and required finish. |
| Fiber disc | Stock removal or surface preparation with an approved backing pad. | Correct backing pad, speed rating and abrasive specification. |
Compare removal per minute, abrasive consumption, rework and operator time. The lowest purchase price does not necessarily give the lowest cost per finished component.
FUJI offers grinding wheels across the 100–180mm range, with availability depending on the series. Compact 100/105mm and 115mm wheels suit smaller equipment and restricted access. A 125mm wheel provides a useful middle option; 150mm and 180mm equipment may suit larger contact areas and heavier work. These sizes are not interchangeable: confirm the grinder's approved diameter, guard, bore, mounting arrangement and maximum speed.
For general steel grinding, 6mm wheels are a common choice, while selected products also offer 7mm. Special-purpose thinner grinding wheels can improve access and control on suitable applications, but a thin cutting disc is not a substitute. Confirm that the exact product is designed for grinding. Thickness alone does not determine service life or prevent heat damage.
Grit size describes abrasive grain size; the grade letter describes how strongly the bond retains those grains. It does not describe the hardness of the abrasive mineral. A lower grit number indicates a coarser abrasive within the applicable grading system.
For example, 24S is coarser and has a harder wheel grade than 36P. A harder grade holds grains more strongly, but is not automatically better: the material, contact area, tool power and grinding pressure affect grain release and self-sharpening. Select by a controlled trial, not the grade letter alone.
| Application priority | FUJI series to consider |
|---|---|
| Economical everyday steel grinding, weld cleanup and deburring | 100mm Super F2 for compact equipment; 180mm Super F2 for suitable larger grinders. |
| Demanding foundry work and heavy material removal | Super Z zirconia grinding wheels. |
| Dedicated stainless steel fabrication | Super W stainless steel grinding wheels. |
| Premium compact grinding with attention to productivity and control | JITAN 105mm and 125mm wheels; select thickness for the task. |
| Semi-flexible grinding and surface conformity | Green Star or FUJI Ace Semi-Flex, according to material and finish requirements. |
| Blending and surface finishing after initial grinding | FUJI flap discs. |
These are selection routes, not interchangeable specifications. Confirm the exact wheel label and approved application. Browse the FUJI grinding wheels and discs range or our product catalogue for available options.
FUJI's Japanese warm-press process, also described as hot pressing, uses controlled forming temperatures selected for the product. Formulation and process control support consistent wheel performance; neither the manufacturing method nor the depressed-center shape alone establishes a universal service-life advantage. Manufacturing location varies by series and should be confirmed on the selected product.
Use visual, label, damage and installation checks for these resin-bonded grinding discs. Do not use a ring test to judge their condition. The clear-ringing test associated with suitable vitrified-bonded wheels is not the inspection method for the FUJI resin grinding discs discussed here.
See the grinding wheel safety standards guide. For the distinction in inspection methods, see Norton's ring-test guidance, which explains its primary applicability to vitrified-bonded wheels.
| Symptom | Checks before changing the process |
|---|---|
| Glazing or poor removal | Check material suitability, wheel grade, contact area and grinder performance. Do not compensate simply by pressing harder. |
| Excessive heat or discoloration | Check dwell time, contact pressure, abrasive choice and grinding sequence. Thin workpieces need particular care. |
| Rapid wheel wear | Check grade, working angle, contact geometry and whether the wheel is being forced or used on an unsuitable material. |
| Gouges or uneven finish | Check contact control and process sequence; a suitable flap disc may be preferable for the blending stage. |
| Unusual vibration | Stop and isolate the tool. Inspect the disc, flanges and grinder before further use; do not attempt to wear an abnormal vibration away. |
Only if that exact wheel is explicitly approved for cutting. A grinding-only wheel is not a cut-off disc, and a cutting-only wheel must not be side-loaded for grinding. Check the label and instructions rather than the center shape.
Follow the angle range specified for the particular wheel and grinder. There is no single angle that covers all rigid, semi-flexible, specialty and combination products.
Do not assume so. Select an abrasive and formulation approved for the workpiece. Aluminum needs a suitable non-ferrous grinding product, and stainless steel work may require contamination controls and dedicated abrasives.
No. Grain retention must suit the job. If dull grains remain in the wheel too long, removal can slow and heat can rise. Compare both abrasive wear and metal removal under the same operating conditions.
Keep them protected from moisture, excessive heat, impact and deformation, using the packaging and storage arrangement recommended by the manufacturer. Observe the marked use-by information and inspect before mounting.
Do not apply bench-grinder dressing practices to these discs unless their manufacturer explicitly authorizes the procedure. If performance deteriorates, check application suitability and condition, then replace the disc when necessary.
Send your workpiece material, weld or casting condition, grinder model and required finish. FUJI can help narrow the wheel series and specification for a practical trial, whether the priority is economical steel grinding, heavier stock removal or controlled finishing.
