Resin bond holds grit mechanically at low temperature; metal bond holds it by sintering or brazing at high temperature. That single difference changes which crystal you buy, whether you coat it, and what size you can use. Specifying one diamond for both bond systems is the most common reason a wheel underperforms.
What Each Bond Does To The Grit
A resin bond is a polymer matrix cured at roughly 150 to 200 degrees Celsius. It grips the particle by shrinkage and adhesion. It cannot withstand high cutting temperature, so the wheel is used wet or at low pressure, and the grit is expected to dull and be released rather than to survive extreme heat.
A metal bond is a sintered or brazed matrix. It is formed at temperatures where diamond can oxidise, and it holds the particle far more rigidly. The grit is expected to stay in place and to take real mechanical load.
The consequences run in opposite directions. Resin needs a grit that cuts freely and releases predictably; metal needs a grit that survives heat and impact.
Resin Bond: What To Specify
Resin bond wheels cover carbide tool grinding, glass edge grinding, ceramic finishing and PCD/PCBN tool work. The useful size band is broad, from 40 mesh for rough stock removal down to 4000 mesh for fine finishing, and most production sits in the 100 to 400 range for grinding and 500 to 4000 for finishing.
For resin, the priorities are:
- Sharp, free-cutting crystal. A blocky high-toughness grit glazes in resin because the bond cannot refresh it.
- Tight particle-size distribution. Resin releases grit gradually; a wide distribution means some particles cut deep while others polish, and the wheel behaves inconsistently.
- Nickel coating where retention is the problem. A light nickel coating gives the resin a mechanical grip and reduces pull-out. It is the standard fix for wheels that shed grit before it has done any work.
Suitable base grades are HDY and HDG at the fine end, and crushed grit such as HDYR in the 80/100 to 325/400 band.
Metal Bond: What To Specify
Metal bond covers saw segments, core drills, grinding cups and CMP pad conditioners. Here the grit is sintered into the matrix, sometimes at over 800 degrees Celsius, and then loaded in a way that fractures weak particles quickly.
For metal, the priorities invert:
- High toughness. The grit must survive clamping and impact. This is where MBD and SMD-class material earns its price.
- Controlled oxidation. A titanium coating at 0.1% to 0.3% by weight protects the particle surface during sintering and improves heat transfer in the cut.
- Coarser sizes. Metal bond tools normally run 30/35 to 60/70 mesh, because each particle has to remove a meaningful chip.
Side By Side
| Resin bond | Metal bond | |
|---|---|---|
| Forming temperature | About 150 – 200 C | Sintered or brazed, much higher |
| Grit retention | Mechanical, by shrinkage and adhesion | Rigid, by matrix clamping |
| Dominant failure | Grit pull-out, glazing | Grit fracture, matrix wear |
| Preferred crystal | Sharp, free-cutting | Tough, blocky |
| Typical size | 80 – 4000 mesh, and W series | 30/35 – 60/70 mesh |
| Coating | Nickel, light to medium | Titanium, thin |
| Typical grades | HDY, HDG, HDYR, HDGR | MBD, MBDS, SMD class |
Where It Gets Confusing
Two cases cause most of the mismatch:
Vitrified bond is not resin. Vitrified wheels are fired at over 1000 degrees Celsius, closer to metal in thermal terms, but they hold grit in a glass matrix that behaves more like resin in the cut. They usually want a free-cutting grit with a titanium coating if firing temperature is high, not a nickel one.
Electroplated tools are neither. A single layer of nickel holds the grit, so retention comes from plating adhesion rather than from the matrix. The correct choice there is a clean, sharp, low-ash crushed grit, often nickel pre-coated so the plating bonds to the coating.
Common Mistakes
- Using coated grit everywhere. Coating is a targeted fix. Putting a 56% nickel coating into a resin wheel changes the particle size and the cost without addressing the real failure.
- Buying toughness you cannot use. A high-TI grit in a resin bond glazes because the bond cannot wear away fast enough to expose new edges.
- Ignoring concentration. Bond performance depends on grit concentration in the matrix as much as on grit type. Changing diamond without checking concentration usually produces an inconclusive trial.
How To Verify
Run the trial in the bond you actually produce. Free-abrasive tests tell you nothing about retention, and metal-bond results do not transfer to resin. Ask for a lot with a documented PSD and, for coated material, the weight gain figure. Then measure wheel life and surface finish over a full dressing cycle rather than on the first part.
Next Step
Resin and vitrified side: resin and vitrified bond wheels. Metal side: saw blades and core drills. Single-layer plating: electroplated tools.
Coating detail is covered in nickel versus titanium coating.