Hi from a Lancashire ex-miner and trepanner operator. The trepanner was the last word in mining machinery in the UK in the late 50's -early 60's. It had a circular cutting head at each end almost the same diameter as the face was high and was pulled up and down the face on top of the conveyer so that (in theory) the coal fell directly onto the conveyer. "Stables" were created by conventional methods at each end of the face so the trepanner could start it's run back straight down the face again after being jacked over into the stable.
Hi Birch Coppice-I once worked at the Smokeless Fuel Pilot Plant at Birch Coppice-remember that-or was it before your time?