Vertex K8400 belt tensioners
Description
This set of tensioners is meant to address the elephant in the room who plagued the performance of four bets 3D printers like. This post treats Velleman Vertex K8400 who in fact has the same design as Ultimaker. The main trouble of this design is that is incredibly hard to keep over time the rods ''square'', that means either you let some great tolerances or try to fix the tension all the time...or accept squicks sounds and skipped layers... All this happened because you really don't have a way to tension correctly the ''damn'' belts. The first sign of malfunctioning is the sounds of bushing or hard working motors...and this is not fun.. What makes these sounds happen is the difference of tension between the upper an lower belt. Some of the users tension the upper belt, this brings some confort but don't solve the problem. I tried lower the tension on the belt with the carrier...with great results but this didn't solve the problem completely. The trouble is that there are THREE ''tension zones'', the long upper belt and the two belt sides with the carrier which acts independently in keeping the rods ''square'', to much tension in front will just drag the rod angled. So to be able to move a bit the rods and having the right tension i figure that it is needed a very small tensioners on each side of the carrier. Varying the length of the belt in the left and right carrier could allow a very precise geometry. Now it would be possible to adjust not only the tension of the three belt zones but also to have an angle correction without work with the pullies. For the vertex k8400 i used also some belt ''risers'' since i observed a bit of misalignment in height. For the long belt there are two types of tensioners, one type for the already ''cut belts'' and one type for original loop belt. The sequence of tuning the belt i tryed with succes is to position the hotend in the middle and check all the tensions in the belts by hand, you may need to increase the tension in the long belt pretty much to keep up with the carrier side segmented belt. After the tensions feel pretty similar just try to walk the hotend and see on which direction is not slide well and adjust the belts on that direction. It helps to push just by the each carrier and if there is an obstruction, you must tension the rear belt side of the carrier belt (and the front from the other side) to modify the angle of the rod. I also use M3 screws with a smaller head to avoid interference between the tensioners, pay attention!
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