Complex sentence: The wooden keys were formed from oak, steam softened and then compressed with hydraulic presses and stored in a drying house; when inserted into the chair, exposure to the wet atmosphere would cause the key to expand, firmly holding the rail.
Split into simpler sentences: The wooden keys were formed from oak, steam softened and then compressed with hydraulic presses and stored in a drying house. When inserted into the chair, exposure to the wet atmosphere caused the key to expand, firmly holding the rail.