A grinding wheel doesn't fail all at once — it drifts out of an effective cutting condition gradually, and the first sign is usually in the part, not the machine. Here are five indicators it's time to dress.

1. Surface finish degrades gradually. A slow decline in Ra over a production run, rather than a sudden defect, usually points to a wheel that's loading up with swarf or going glazed rather than a machine or fixturing problem.

2. Grinding sparks change character. A wheel cutting well produces a consistent, fine spark pattern. Sparse, heavy, or intermittent sparking with the same feed and speed settings suggests the abrasive grains have dulled or the wheel has loaded.

3. Part temperature rises. A glazed or loaded wheel rubs more than it cuts, generating more heat for the same material removal rate — a real risk for thermally sensitive parts and one of the reasons a rigid, thermally stable machine bed matters as much as the wheel condition itself.

4. Feed pressure or spindle load creeps up. If the machine is working harder to maintain the same feed rate it held cleanly a shift ago, the wheel's cutting efficiency has dropped.

5. Out-of-round or taper starts appearing. A wheel that's gone out of true transmits that error directly into the part's geometry — often the first hard evidence something upstream needs attention.

None of these signs demand guesswork on a modern CNC grinder: dressing cycles are typically programmable and run in well under a minute, and catching the drift early is far cheaper than the scrapped parts that come from ignoring it.