Shimming Coffee Grinder Burrs: What Burr Shims Do and When Alignment Work Makes Sense
Shimming is the use of very thin material beneath selected points of a grinder burr or burr carrier to correct an alignment error. The technique is most often associated with improving burr-face parallelism, but it should be treated as a targeted mechanical correction rather than routine grinder maintenance.
What a shim changes
A shim slightly raises one area of a burr or carrier. By changing that local height, the burr face can be tilted by a very small amount relative to the opposing burr. Thin foil or purpose-made shim stock is commonly used because the required correction may be only a fraction of a millimeter.
Why burr alignment matters
If opposing burr faces are significantly non-parallel, the burr gap can vary around the circumference. That can change contact at mechanical zero and may affect particle distribution. However, grinders have manufacturing tolerances, and perfect theoretical contact is not required for every grinder to produce excellent coffee.
Before adding shims
- Confirm the burrs and mounting surfaces are clean.
- Make sure burr screws are tightened evenly.
- Rule out debris beneath a burr.
- Check for damaged carriers, bent parts, or excessive runout.
- Use a repeatable alignment test rather than judging from one brief sound.
Marker tests and limitations
A marker wipe test can show relative contact around a burr face, but the result depends on how lightly the burrs touch and how the test is performed. It does not directly measure grind quality. If a grinder is producing consistent, good-tasting coffee, alignment work may offer little benefit and introduces a risk of making the setup worse.
After shimming
Recheck alignment, verify the burrs rotate safely, and recalibrate the grinder's zero point. Never allow burrs to run hard against each other.
Browse home coffee grinders and read more terminology in the Coffee, Espresso & Brewing Equipment Glossary.
