I built an iteration 2 prusa and love it. There are a few well known problems with the design and I've solved most of them. One solution that proved particularly valuable to me, was supports for the ends of the Z threaded rods, taking the weight off the coupling bits and Z motors. I've been printing for over a month without the need to adjust the Z end-stop or level the bed.
My models are linked below. Warning, you will need a 3D modeler and some experience at modifying models. The dimensions will need to be tweaked to meet your machines needs. There's a video among the photos, it explains things visually.
Kevin.
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www.thingiverse.com]
