Worden Mk3 - 4-Facet Drill Grinding Jig

Compared with conventional cone ground drills, 4 facetted drills require a marked reduction in drill pressure and show a reduced tendency for even long drills to wander.

This recent design from Jim Whetren will accommodate drills from Ø3/32" to Ø1/2" (standard, countersink or flat bottomed). The clearance angles chosen for the 2 cutting lips are those used by the late Professor Chaddock, namely 30° for the first grinding then 10° for the second and final grind.