By the mid 15th century the workings were so deep that drainage was once again a problem. In an area where few deep valleys cut the productive deposits, deeper free drainage could only be achieved by the use of long crosscutting adits. A problem aggravated by the increased cost and scarcity of labour brought about by a prolonged period of population decline. In the 1470's, with interest apparently centred on a possible source of rich ore north of Lockridge Hill, mechanisation using water powered suction lift pumps was introduced in an attempt to overcome the problems of drainage. That is only 50 years after suction lift pumps were first attested to in Italian documents and only two decades after their first use in the mines of central Europe.

With no system of power transmission available it was necessary to bring the power source, water, into the mine at the shaft head. That entailed a leat, or watercourse, 16 kilometres long tapping tributaries of the River Lumburn at Millhill west of Tavistock and careful surveying was required to bring the water over a shallow saddle in the ridge, between the Tavy and Tamar rivers, near Higher Gawton. The line of that leat can be traced over much of its route particularly on the steep west bank of the Tavy where it has been cut through solid rock. A unique physical link with the introduction of innovative technology in the late medieval period.

The preparation, smelting and refining required to process the silver-bearing ores were an integrated part of Crown operations at Bere Ferrers. During the first few years of operations in the late 13th century production was based on the wood fired, wind blown 'bole' smelting technique brought from the lead mining areas of northern England. However the bole was not capable of efficiently smelting all the ore mined and was soon augmented by charcoal fired, bellows blown furnaces developed through a period of experimentation. Transport by horse and by river played an important part in the processing operations. Ore was moved from the mines to washing sites where waste was removed by simple gravitational separation. From there it was taken to one of a number of smelting sites. Bole smelting sites were located as far afield as Milton to the east of the Tavy. Residues from smelting were removed for crushing and washing to separate the waste. Those parts still rich in lead and silver were then re-smelted in the furnace.

Until 1301 the lead produced was refined at a mill near Martinstowe (Maristow), on the Tavy estuary.4 Refining, furnace smelting and most of the bole smelting operations were then moved to Calstock, on the Cornish bank of the Tamar. Remaining there until circa 1318 when they were returned to Martinstowe. The smelting / refining operations consumed large amounts of fuel drawn from woods at Warleigh, Bickham, Halsere (in Bere Ferrers) and Morwellham. When the mines were granted wood from the manor of Calstock it was easier to move the ore to the fuel and centre activity around the church there.

Working during the early modern period appears to have been concentrated at Buttspill, on the crosscourse north of the medieval workings, where a 'silver mine' was active in the 1690s. However, much of the ground worked during the medieval period was re-examined during the late 18th and 19th centuries when, with the advent of powerful steam pumping engines, workers were able to get to new ground below the medieval workings. A testament to the drainage skills of the earlier miners. As a consequence later activity was concentrated on certain deep shafts leaving much of the old surface workings untouched.