A guided string acid saw for the strain‐free planar cutting of oriented single crystals is described. A Saran monofilament used as the acid carrying element is guided completely through the cut by a grooved blade serving the three‐fold purpose of guide, pressure device, and follower for a position sensing mechanism which automatically controls the feed. Guiding of the string results in a width of cut to string diameter ratio considerably lower than that of unguided acid saws. Bismuth and copper crystals have been cut with excellent results using this device.