bench grinder vs bur

bench grinder

noun
  • A grinder, typically with a pair of grinding wheels (one at each end of the motor shaft) that is designed to be permanently mounted on a workbench. 

bur

noun
  • A rotary cutting implement having a selection of variously shaped heads. 

  • Any of several plants having such husks. 

  • A rough, prickly husk around the seeds or fruit of some plants. 

How often have the words bench grinder and bur occurred in a corpus of books? (source: Google Ngram Viewer )