In this paper, the technical characteristics of text/graphics segmentation of engineering drawings, its critical steps and basic processing framework are analyzed. The SegChar, a practical tool for automatic text/graphics segmentation developed by the authors, is presented. The emphasis is put on two technical respects: (1) the automatic text size threshold method, which makes the processing procedure automatic and intelligent; (2) the probing strategy for extraction of text strings of arbitrary direction and length, which can extract Chinese/Western character strings integrally, and enhances its performance in processing speed, space complexity by introducing the concepts of accurate HOUGH space requirements, collinear relaxation and the string based HOUGH field refreshing method. The performance evaluation of SegChar is given finally.