Coal seam test drill guide sleeve - has ball bearing mount with fin projecting each side to engage inside of hole

摘要

The drill for making test bores in coal seams has a rod (1) with a spiral cutting blade (2) around it, which is interrupted for attachment of a guide sleeve (4). This sleeve consists a thick walled lower half (5) onto which is bolted a thin walled upper half (6), both of a smaller dia. than that of the spiral blade. Each half has a radial blade (8, 9) along it, with a pointed tip which can dig into the sides of the bored hole. Both ends are supported by ball bearings (11) running in tracks (12) around the spindle inside, to allow the spindle to rotate. An alternative device houses a direction indicator such as a magnetic compass, or a spirit level.