How do I know if my grinder burrs are aligned?
Run the marker test: colour the flat face of one burr, run the grinder briefly with no beans at a setting where the burrs just touch, and see where the marker is removed. Even removal all the way around means aligned, removal on one side means misaligned.
Alignment means the two burr faces are parallel to each other as they rotate. When they are not, the gap is narrower on one side than the other, so part of the coffee gets cut finer and part coarser on every rotation. The result is a wide particle distribution regardless of the setting you pick, which is exactly the defect a good grinder is supposed to avoid.
The marker test is the standard diagnostic. Remove the burr carrier, colour the flat cutting surface of one burr with a permanent marker, reinstall it, and with no beans in the grinder bring the setting down until you just hear the burrs chirp against each other. Run for a second, stop, and remove the burr again. Marker removed evenly around the full circumference means the faces are meeting parallel. Marker removed on one arc and untouched on the opposite arc means the burrs are meeting at an angle.
The usual fix is shimming. Thin shims, sold as kits for popular models or improvised from adhesive foil tape, go between the burr and its mounting surface on the low side to tilt the plane back to parallel. It is fiddly and iterative: shim, retest with marker, adjust. Expect several passes. Work in small increments, since a shim that overcorrects simply moves the problem to the other side.
Do this test before you spend money on upgraded burrs. Premium burrs in a misaligned grinder perform worse than stock burrs in an aligned one, because the geometry that makes them good depends on the faces meeting correctly. This is the most common way people waste money on a grinder upgrade.
Two honest limits. Conical grinders are far less sensitive, because the cone self-centres within the ring to a degree, so alignment work on a conical usually has a smaller payoff. And on some machines the misalignment is in the motor shaft or the housing casting rather than the burr seat, in which case shims can only partly compensate and you are looking at a warranty conversation instead of a weekend project.