A method of forming a gate valve for use in a high vacuum environment of an electron gun by machining a core of non-magnetic nickel-chromium-molybdenum-iron-tungsten-silicon-carbon alloy that is weldable with nickel alloys and has a tensile strength of about 750 megapascals, machining a cladding of nickel-iron, welding the core to the cladding to form the gate valve, and machining the gate valve so as to remove any dimensional differences at an interface between the core and the cladding. In this manner, because the final mechanical tolerance is controlled by machining instead of part assembling, extremely high alignment accuracy is obtained. The final part provides field shielding as provided by the nickel alloy shell, low stray field provided by the non-magnetic alloy, good vacuum performance, and tight mechanical tolerance control. Also, because the alloy has the advantage of a low oxidation rate in comparison to stainless steel and titanium, there is less contamination buildup due to conditions such as electron beam bombardment.