How fast is too fast for a marble machine? Well, check out the video "Marblevator Mini, Loop High Speed Test", at 324,000 marble runs per day, it is indeed the fastest marble machine I've ever designed: https://www.youtube.com/watch?v=mumoRD_TPWQ. And the stress test: https://www.youtube.com/watch?v=-RsX8fvJLVE And the normal test: https://www.youtube.com/watch?v=8Ve0sO8ITDM I had to dust off my physics textbook for this one... "Marblevator Mini, Loop" is not quite as "mini" as my previous Marblevator Mini designs, but is still quite small, and features a 7.5mm radius loop with a tapered auger lift. Using a few relatively simple physics equations, the height of the entrance ramp (H) is determined by the simple equation H = 2.7R (where R is the radius of the loop). My desire to keep the model small determined the loop radius (7.5mm) and ball bearing diameter (8mm). And to add friction compensation, especially for a 3D printed track printed in this orientation, I increased the height of the ramp over the calculated height of (2.7 * 7.5mm) or 20.25mm. In the video "Marblevator Mini, Loop Stress Test", the stress test ran over 29 hours and is still running. The auger rotates at approximately 75rpm which in this test translates to 75 marble runs per minute. At this rate, Marblevator Mini, Loop has executed (29 * 75 * 60) or 130,500 marble runs without loosing a marble. Requiring only three 3D printed parts (base, track and auger),the track part may indeed test the limits of both you and your 3D printer. I've printed the track both with PVA support and without support at .1 and .15mm layer heights and discovered that on my printers with PVA support, no filing or sanding of the track was required. If no support material is used, you most likely will need to file and sand the inside edges of the track until reliable operation is obtained. As usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make mistakes in plenty. Designed using Autodesk Fusion 360, sliced using Cura 3.3.1 and printed in PLA on both an Ultimaker 2+ Extended and an Ultimaker 3 Extended.