chaffer

A chaffer is the upper sieve deck in the cleaning shoe assembly of a combine harvester. Its job is straightforward: it removes the bulk of chaff, broken straw, and light debris from the grain stream before it reaches the lower sieve. The chaffer sits directly below the grain pan that receives material from the threshing drum, positioned to catch and reject everything lighter than whole grain.

The chaffer consists of a flat or slightly curved screen made from woven wire or perforated steel, typically with openings between 3/8 inch and 5/8 inch depending on the crop and machine model. As the shoe vibrates, properly sized grain falls through the chaffer openings and drops to the lower sieve, while chaff and small debris bounce and travel backward, eventually exiting the machine through the chaffer outlet. The angle of the chaffer bed and the frequency of vibration both control how aggressively material is processed.

Chaffers wear and clog easily. The screen becomes plugged with fines and small particles, reducing airflow and separating efficiency; combine operators typically clean or replace chaffers during the season depending on conditions. A worn chaffer with enlarged openings allows grain to escape with the chaff, while one that is too restrictive causes buildup and reduces capacity. Different crops and moisture levels require different chaffer configurations, so operators may swap screens between jobs.

The term itself follows the old English word chaff, the dry husks and plant material separated during threshing. The chaffer does the work of chaffing, making it the tool that performs the action. It sits in a wider cleaning system: grain falls through the chaffer, then through the lower sieve (which removes finer material), while air currents from the fan carry away the lightest waste. A properly tuned cleaning shoe depends on all three components working together.