mortar, grind
碾 centers on crushing or pulverizing something into fine particles using a heavy tool: grinding grain or using a mortar.
碾 combines 石 (stone) with 展, which likely contributes the sound and the idea of spreading or pressing down, suggesting a stone tool used for grinding.
The left side is a stone 石, and the right side 展 suggests spreading out. Picture a heavy stone wheel spreading grain flat as it grinds it into powder.
For テン, imagine grinding with a stone mortar inside a tent: tent -> テン, and the stone crushes the grain.