Prusa MK3 Bear 20T 5ID Gates Y idler + tensioner

thingiverse

Rework of the original Y idler by Greg Saun for the MK3 Bear 2.0 full upgrade featuring a belt tensioning and tracking mechanism utilizing a Gates 20T 5ID toothed idler. For an alternative version using the stock 20T 3ID smooth idler, refer to my previous remix on Thingiverse: [https://www.thingiverse.com/thing:3475507](https://www.thingiverse.com/thing:3475507). This upgrade is specifically designed for the Bear 2.0 full upgrade and uses the stock MK3 Y belt holder to maintain a straight belt path, making it incompatible with the MK3S and/or Bear 2.1 upgrade due to different belt alignment requirements. **Bill of Materials (BOM):** - 1x Gates 20T 5ID toothed idler - 1x M5x20mm screw - 1x M5 nylock nut - 2x M3 thin square nuts (taken from MK3 parts) - 2x M3x10mm screws (MK3 parts) **Printing:** Print with the same parameters as for the original design, using 0.2mm layers, three perimeters, and 30% infill. **Assembly:** Insert the thin square nuts through the central side slot from the front. The hole is intentionally tight, so handle them carefully. Center each nut perfectly by pushing on the side slot using a flat screwdriver; avoid using an hex key or screwing onto the thread, as this may damage the nut due to its snug fit. Install the belt and idler, then secure the M5x20mm screw with the nylock nut. Do not apply excessive force, as it should not bend inwards. The thread only needs to reach the nylon insert; lateral play is acceptable. Push the screw/idler towards the front and install the M3x10mm screws from the front until they just touch the screw and bolt. A drop of low/medium strength thread-locker is recommended for added stability. Loosely attach the idler to the frame. Pre-adjust the belt under the Y carriage until it has some tension, as this idler allows for 1.5 teeth of adjustment. Center the idler by pulling the carriage towards it. For optimal alignment, visually center the entire belt first, ensuring it remains straight. Then, fully tighten the idler on the frame. Proceed to tighten the belt in small increments and at the same rate until the desired tension is achieved. Finally, fine-tune the belt tracking by adjusting one screw only while moving the carriage to ensure the belt stays centered. This method allows for precise alignment of all components in a straight line, unlike shifting a regular idler left or right. The final depth of the screws may not be identical due to nut shape and axis adjustment variations; therefore, rely solely on belt alignment verification rather than screw insertion depth.