偏芯[henshin] eccentricity (in mechanics, electronics, etc.)
燈芯[toushin] (lamp) wick
帯芯[obishin] thick obi sash
摘芯[tekishin] thinning (buds and branches)
芯地[shinji] padding

替え芯[kaeshin] spare lead
鉛筆の芯[enpitsunoshin] lead of a pencil
硬の芯[kounoshin] hard pencil lead
林檎の芯[ringonoshin] core of an apple

研鑽[kensan] diligent study
鑽り火[kiribi] striking sparks with flint and steel or by rubbing sticks together (usu. to start a fire)
鑽孔機[sankouki] boring machine
鑽り出す[kiridasu] to quarry

鑽孔[sankou] boring
鑽る[kiru] to start a fire (with wood-wood friction or by striking metal against stone)
自己研鑽[jikokensan] self-improvement
火鑽り[hikiri] hand drilling (to start a fire)