A sample preparation apparatus and method of preparing a rock sample using such an apparatus, as useful in connection with the digital numerical simulation of properties of the rock. The disclosed apparatus includes a fixably mounted diamond wire cutter. Three linear translation stages are coupled to a specimen holder. One of the translation stages moves the specimen in a direction parallel to the plane of the cutting wire. The other two translation stages move the specimen in different directions from one another, and when actuated together, advance the specimen into the wire for short distances in a direction out of the plane of the cutting wire. Short piecewise linear cuts are made in the specimen, to provide a sample of the desired shape with a small cross-section.