A method of making a three-dimensional object by additive manufacturing from a blended resin (e.g., a blended dual cure resin), the blended resin including (i) at least one light polymerizable first component and, (ii) optionally but preferably, at least one, or a plurality of, second solidifiable components that are different from said first component, the method including one or more of the steps of: (a) providing a first resin and a second resin, where the resins produce three-dimensional objects having different mechanical properties from one another when all are produced under the same process conditions; (b) mixing the first and second resins with one another to produce the blended resin, the blended resin producing a three-dimensional object having mechanical properties intermediate between that of objects produced by the first and second resins when all are produced under the same process conditions; and (c) dispensing the blended resin to the build region of an additive manufacturing apparatus; and then (d) optionally but preferably producing a three-dimensional object from the blended resin in the apparatus.