Rapid manufacturing processes have been used in multiple aerospace applications, including ductwork [5] [6] and a capacitor housing on the International Space Station [9]. These applications used selective  laser sintered nylon parts, which established a basis for rapid manufacturing as a viable method for  producing parts. Structural brackets [3], a shrouded cryogenic impeller [3] [10], and brackets for the Juno  spacecraft [7] have also been manufactured in titanium using rapid manufacturing processes. While most parts built thus far have been structural members (brackets, etc.) or non-structural assemblies (ductwork  and housings), in our work we use additive manufacturing to create monolithic mechanisms for aerospace  applications. As part of that effort, it is desirable to know what to expect when printing slender geometries, and maximum allowable stresses in EBM-produced titanium parts. Material Considerations Porosity of EBM produced parts EBM produced parts can achieve full density [11]. Wooten and Dennies claim that the fully dense region  occurs in bulk parts about 1.25 mm (0.05 in) below the surface [3], but give no explanation of how this figure was arrived at. This depth is more than the thickness of many printed flexures. While the region  near the surface may not be fully dense, Murr et al, mention that such micropores have no effect on shortterm tensile properties [12]. However, surface roughness and micro-cracks contribute to reduced fatigue  life. Because of the slender geometry, machining of flexures is often impractical, so surface porosity is difficult to eliminate and must be accounted for in the design. This surface porosity constitutes a major obstacle to high cycle fatigue life. Hot isostatic pressing (HIP) improves the fatigue life of EBM produced  parts [13]. If HIP treatment is impractical, property data obtained from raw (not treated with HIP or finish machined) tensile samples are available [14].   Thickness Correction Factor Early design work for a two-degree-of-freedom (2 DOF) pointing mechanism [15] required testing the  fabrication and performance of cross-axis flexural pivots. These flexures have a number of good characteristics, including good stability and load carrying capacity [16]. The flexure was modeled in  ANSYS to predict its torsional stiffness, which was compared to analytical solutions. Finally, the flexures were produced using EBM, and an example is shown in Figure 2, along with the pointing mechanism.  The torque and deflection characteristics of three printed flexures were found. The FE model significantly  over-predicted (~30%) the stiffness of the printed. Because of high surface roughness, it was thought that  perhaps not all of the thickness of the flexure contributes to its bending stiffness. Applying a correction factor of 0.83 to the thickness resulted in good agreement between the FEA and measured stiffness of  the flexures. Later this correction factor was used to predict the overall stiffness of the pointing mechanism, again resulting in good agreement. Therefore, when using thin flexures, a thickness correction factor of 0.83 is recommended to accurately predict the torsional stiffness of printed flexures.  Figure 2. Cross-axis flexural pivot and 2 DOF pointing mechanism used to compare FEA and  analytical models to measured stiffness. 170