Crimping machines comprising a stuffing chamber with a rectangular cross section and two rollers, between whose generated surfaces there is a narrow roller gap for delivering a bundle of synthetic threads, are widely used. Generally, the stuffing chamber is surrounded by smooth fixed delimitation surfaces. In operation, heat is generated as a result of the friction between the delimitation surfaces and the clump of threads located in the stuffing chamber. The novel crimping machines can operate at very high speeds without melting occurring as a result of heating caused by friction. The first roller (1) is provided at its front ends with flanged wheels (4, 5) which enclose the other roller (2) with slight play. The stuffing chamber is located in the annular duct between the flanged wheels (4, 5) such that their inner faces form two opposite delimitation surfaces over the entire length of the stuffing chamber (60) from the roller gap (3) to its mouth (61). Preferably, the mouth (61) of the stuffing chamber (60) is disposed at a spacing from the plane (62) of the roller gap (3), namely on the side on which the first roller (1) is located. The two rollers (1, 2) are equipped with motors (19, 22) which are designed for a peripheral speed of the rollers (1, 2) of up to at least 1000 m/min.