I recently purchased my 840/2 system and I'm still getting familiar with it. Today I've been adjusting the two y-axis lead screws to make sure that the x- and y-axis are orthogonal. While working with this, I discovered that my belt was walking a lot left/right while jogging. I just want to share my tip to use a couple of layers of Kapton tape for shiming it so that the belt runs straight. In my case, three layers did the trick. This might be worth including in the assembly manual because the belt was walking quite a lot unless adjusted. An instruction video might be helpful.
I realized that I failed to mention that the adjustment was done to the belt tensioner. Sorry about that.
The links to the videos below show before and after videos. The Kapton was inserted on the right hand side of the belt tensioner in this case to take out the angle error of the roller bearings that caused the walking.
I prevented "jumping off" at the belt adjustment by replacing the first ball bearing with one that has a flange.
that works fine to me.
furthermore I invented a srew holder on the inside of the machine, that holds the srew in place always. therefore I can release or tighten the screw without a nut falling of. that makes the whole process a lot more comfortable.
the last thing i made was a hole into the belt cover. that i can adjust the belt without removing the cover
That sounds like another way forward, but I wanted to avoid wear on the side of the belt so shimming felt right for me. The hole in the cover sound convenient. Do you find that you have to change the tensioner from time to time? In other words, should I keep an eye on this?
well every time I do a hole clean up of all axis and stuff i untighten the belt. and shortly after that I sometime be a bit concearned if erverything works fine. therefore its a huge plus in setting the machine up!
long story short. YES I am absolutly enjoying my way