Prusa MK3 Bear Full Upgrade length-adjustable X idler

thingiverse

Rework the stock MK3 R3 X idler for +/- 1mm rod length adjustment, which is secured using two M3x8 screws. This modification is valuable mainly for custom builds like the full bear upgrade. It's unlikely to be useful for plain MK3 or bear half-upgrade assemblies. When printing at maximum up or down speed, observe if the Z screws flex in opposing directions due to rod-length mismatch in your assembly. Note: If they displace randomly, then length is not an issue (release tension from POM nuts, recheck). If the screws don't touch the hole in Z tops, you're still good. But once noticed, your OCD will kick in and deep down you'll feel compelled to fix it since "good enough" isn't our goal. Print at 0.2mm with 0.1mm for the first layer (this improves rod center alignment) or 0.3mm throughout. Use three perimeters at 30% grid infill. Drill holes with an 8mm drill and check, clean any debris especially in pockets. Insert M3x8 screws which will self-tap holes. Keep moving screws until they don't squeak anymore: you'll need some feel for tightening later. Insert rods and push them fully. The assembly should be 1mm shorter than stock length. Tighten screws until you feel tension due to rods touching. Insert assembly into Z screws/rods. Insert Z tops to align POM nuts and tighten, but do not yet tighten Z tops. Move carriage fully down and observe direction of Z screws: if they go inwards, rotate 1/4 turn of both screws and repeat by moving carriage up and down again. Go slowly: if screws start going outwards, rods are too long. Due to X rod fit it's hard to shorten carriage. Remove assembly and push rods fully back before trying again.