Robert Staines has the trepanner used at the tunnel colliery exactly right, according to my memory (I was 18 when the Tunnel, which was the usual name for Haunchwood Colliery, closed down. The colliery was near, and under, a railway tunnel.)
No doubt there were several types, but the ones I saw were like a half-open pocketknife, the (handle) body dragging itself along the coalface, and the (blade) chainsaw-like cutter undercutting the coal perhaps 2metres deep. The machine operator was also called the Trepanner.
The shotfirer blew the coal, and the 'Strippers' pick-and-shovelled it onto the belts, which took it to the main 'Jig' from the middle of the face where a bigger belt took it to where it was loaded into 'minecars' which are small railway trucks, took it to the 'Pit Bottom' and so up to the 'Pit Bank' or surface. Of course, everthing had to be reset after each 'Stint,' the face belts moved, the main belt lengthened, the face props exchanged for scanty Pack props in the waste space behind the face, which slowly (if you were lucky) closed down. Hard, dangerous, and dirty work.