Upgrade your arms! Have you been having issues with your MakerBot Replicator HBP arms warp and sag? The Replicator is a Revolutionary 3D printer pushing the limits of small scale 3D printing. As people reach new advances in desktop 3D printing, stability and consistency are critical. The original HBP arms are made of ABS plastic. Unfortunately, when the plastic arms are exposed to the heat generated by the HBP, they warp, sag, and otherwise move. This warping and sagging make it incredibly difficult to have a consistently level HBP. As a result, constant tweaks and adjustments are required. Another issue with the arms is the low mass. During high speed printing, the original, low mass arms, lightly vibrate. These vibrations contribute to further distort the object being printed. Virtually eliminate these issues by upgrading to custom CNC milled aluminum HBP arms. These replacement arms are made out of a single solid piece of 6061 aluminum. I printed these out at 120mm/sec (Thanks to Sailfish!). ABS Plastic 15% Infill/Octagon Pattern. .27mm layer height. I printed with full support, but with NO raft. I've added a revised STL for all arms shipped 3/18/13 and later that are being installed in a Replicator 1. The older arms used different lower bearing retainers.