DEERFIELD — A Massachusetts man who police say left a bomb at his workplace has pleaded not guilty.Nelson LaCaprucia, of Easthampton, entered his plea Thursday on a charge of manufacturing an explosive, incendiary or destructive device.The 46-year-old worked at Trew Stone Inc., a stone products supplier in Deerfield. Police say LaCaprucia made the device at work while off the clock.Authorities found the device Wednesday and evacuated the building.