Abstract— Chemical machining has a considerable value in the solution of machining problems that are constantly arising due to introduction of new materials and requirement for high surface finish and dimensional accuracy, complicated shape and special size which cannot be achieved by the conventional machining processes. The present work is aimed at studying the effect of machining temperature, machining time, and previous cold working on the metal removal rate and the surface finish of chemically machined samples of stainless steel 420 using a mixture of acids (H2O + HCl + HNO3 + HF + HCOOH) as an etchant. Alloy samples of (44.5×44.5×3mm) dimensions and cold rolled alloy samples with the same dimensions were chemically machined. Four machining temperatures (45, 50, 55, and 58oC) for each of which five machining times (2, 4, 6, 8, and 10min) were used as machining conditions. The results show that machining time, machining temperature and previous cold working have significant effect on chemical machining products, among these variables machining temperature has the largest effect. Surface roughness increases with the machining temperature and machining time, while it decreases with the previous cold working. Metal removal rate increases with machining temperature and decreases with previous cold working. Stainless steel 420 rolled samples can be chemically machined in [H2O + HCl + HNO3 + HF + HCOOH] etchants in optimum conditions at 40?C for 6 min, while at 40 ?C for 6 min for the samples without cold working. An assessment of CHM was achieved by empirical modelsfor selecting the appropriate machining conditions for the required surface roughness and metal removal rate. The models were designed basing on multiple regression method via Mtb14 software.