Matrix engraving by electron beams

In an apparatus for producing engraved printing forms via an electron beam device which is located in a vacuum chamber having an open side facing a peripheral surface of a printing form cylinder and defining therewith an air gap, and an arrangement for effecting relative movement of said vacuum chamber and printing form cylinder while maintaining said air gap, the improvment comprising:

• an annular member having an outer circumferential surface of a diameter corresponding to the outer diameter of said printing form cylinder, said printing form cylinder having a trunnion;
• cooperating annular bevelled contact faces provided on respective axial ends of said annular member and printing form cylinder, and
• a mounting device for said annular member secured on said trunnion and mounting said annular member for displacement axially of said printing form cylinder,
• so that, when said contact faces are coaxial and urged into abutment with one another, said outer circumferential surface constitutes an extension of said peripheral surface.