Metal vs resin bond: which wheel for which station

The bond decides how the wheel wears, not how fast it cuts. A station-by-station comparison for rough, fine and polish positions on glass edgers.

The bond controls wear, not cutting speed

Buyers usually compare bonds on how fast the wheel cuts. That is the wrong axis. On a glass edger both bonds cut at a similar rate when they are fresh — the difference is what happens over the next forty hours. Metal bond holds its shape and keeps the edge geometry; resin bond keeps renewing its own cutting face and leaves a shallower scratch. Choose by what the next station has to remove, not by the first metre.

What the two bonds actually are

Metal bond is diamond held in a sintered metal powder matrix. The matrix is hard, so it wears slowly and the diamond is used up before it falls out. That is why a metal-bond wheel holds diameter and profile through a long run — and why it glazes instead of self-sharpening when the coolant is weak.

Resin bond is diamond held in phenolic resin on an aluminium or bakelite body. The resin wears back steadily and releases dull diamond before the heat builds up. The trade is life: a resin wheel gives up diameter faster, and it will not survive a dry pass.

Station by station

Station	Bond	Typical grit	If you fit the wrong one
Rough / stock removal	Metal, sintered	#46 – #100	Resin heats, smears and rubs instead of cutting
Medium	Metal, or resin on thin glass	#100 – #180	Too coarse here leaves damage the fine station cannot clear
Fine grinding	Resin	#180 – #400	Metal scratches; polishing then has to remove scratches, not haze
Polishing	Polyurethane or felt with cerium oxide	—	Not a diamond-bond question

Why the rough station is almost always metal

Rough grinding removes the most material of any station, and it has to hold a straight profile while doing it. Resin at this station does not fail dramatically — it starts cutting, heats up, the resin smears and the wheel begins to rub. The operator sees a grey, shiny edge, adds pressure, and makes it worse. If a resin wheel is on station one, that is usually the whole problem.

Why fine grinding is almost always resin

Fine grinding is not about removing material. It is about removing the subsurface damage the rough station left. A resin bond with #180–#400 diamond cuts shallow, cool and consistently, which is what the polishing station needs to finish from. A metal wheel at this station can hit the tolerance and still leave scratches that only appear after polishing.

Three signs the bond is wrong for the station

The wheel glazes in the middle of a shift and needs dressing more than once a week.
The edge reads grey after polishing while the wheel still has layer left.
Amp draw climbs steadily through the shift on a machine that used to hold flat.

None of these proves a bond problem on its own. Together they usually do.

The rule we give customers

Rough: metal. Fine: resin. Polish: polyurethane, not diamond. The middle stations are where judgement is needed — glass thickness, removal per pass and spindle rpm decide whether a finer metal wheel or a resin wheel fits better.

Where the rule bends

On 2–4 mm solar and technical glass the removal per pass is small, and a fine metal wheel can hold tolerance through a long run where resin would wear out of spec. On 19 mm laminated glass the interlayer loads the wheel differently, and the rough station usually steps one grit coarser (#60–#80) rather than changing bond. Both cases are still metal at rough, resin at fine.

What to tell us

Machine brand and model, spindle count, the wheel you run now (outer diameter, bore, work layer), glass thickness, and the finish you need. With those five we can name the bond and grit sequence per station instead of guessing.