Abstract: An automatic grinding machine adapted to cut and relieve spiral drill flutes and perform analogous form-relieving operations requiring helical advance of the work, wherein a linearly-moving carriage travels a rotary spindle and its work chuck relative to a grinding wheel in programmed duty cycles under control of logic circuitry with optional manual override control. Separate electric motors for the carriage and spindle are activated at adjustable speed ratios by digitally set binary drive pulses enabling instant change of helix angle or lead ratios and other working parameters by adjustment of digital switches at a simple control panel. A reversible tool head affords automatic cross-cutting capabilities; and a system of pulse-controlled indexing of the work is provided to increase the production rate of the machine by a method which effects the indexing as a function of the otherwise idle return travel of the carriage for restarting in successive work excursions.