Electro-chemical discharge machining (ECDM) is a recent technique used to machine insulating materials like glass and ceramics. This paper presents the results of the combined effects of tool feed-rate and tool shape on the micro-machining of a quartz substrate using an ECDM process. The investigations show that a tool with a spherical tip provides a profile with a reduced entrance diameter and the overcut can be considerably reduced by controlling the tool feed-rate. © 2015 IEEE.