Although there are other conceivable options, the most obvious way to get the IDs within tolerance is milling. By using either a CNC toolpath on an end mill, or a boring bar on a conventional mill, it should be very easy to get well within .006" of nominal dimensions on both areas of the part. However, the issue of fixturing is nontrivial. I designed this part with T-splines, and its outer surfaces aren't orthogonal at all. As a result, we'll need custom tooling to hold the parts in a milling vise.

As an aside: Anyone who says that additive manufacturing eliminates the need for custom tooling has no idea what they're talking about.

In order to securely fixture this part, Rob is machining its negative into a set of aluminum blocks, which can then be clamped securely into a milling machine vise. This technique (which I'll refer to here as "soft jaws," although technically what we're making is more of a coped fixturing block) is used extensively in subtractive manufacturing to hold irregularly shaped parts.

The process of making soft jaws is relatively straightforward, but designing them for this part is somewhat complicated by the dimensional variation that EBM produces. Put simply, feature sizes in EBM parts tend to deviate from the design in the X and Y axes, but stay relatively true to size in the Z. That's because the Z axis is at least partly controlled by the Z stage drive system; the powder bed is lowered a predictable amount with each new layer, keeping features in the Z close to their designed dimensions. But in the X and Y, deviations in feature size are partly driven by the electron beam diameter, and partly driven by the distance that the feature is from the center of the build platform.

As a result, my part has grown anisotropically, and Rob will need (to some extent or another; soft jaws tend to be somewhat forgiving) to compensate for the as-printed dimensions differently in the XY plane than he does in the Z.