Precision is Planar: How to Hold the Tightest Tolerances in SLS

For a cylindrical part made through selective laser sintering (SLS), how should the part orient within the build?

For a cylindrical part made through selective laser sintering (SLS) additive manufacturing, how should the part orient within the build: lying down or pointing up?

Answer: If the roundness of the cylinder is important (as it probably is), then the answer is pointing up. The precision of SLS occurs in the X-Y plane. So let this plane produce every circular cross-section of the part, all the way up.

The set of cylindrical parts seen on in the images on this page illustrate the potential problem. The axial length of the locking features protruding at one end of one of the parts is also a critical dimension. Pointing the part up puts this dimension, the length of the feature along the axis of the part, fully parallel to Z and therefore fully removed from the X-Y plane.

Here is the answer that worked for this part: Size the key length in increments of layer height. In SLS, the layer height is the Z motion, and while this height might represent a coarse increment, it is tightly repeatable from layer to layer.

This part is a real production case produced by Lifestyle Additive, a specialist in SLS. Nate Stevens of Lifestyle Additive and I have been working on a series of videos about designing to make full use of SLS’s special capabilities. The latest video (discussing this part and others) is about how to design for SLS to fully realize its tight precision: