Kossel Mini
Improved Sliders
One of the biggest remaining issues with my Kossel Mini is the wobbly sliders/carriages. The slider bearings supplied with the kit are very low quality which results in excessive play in the effector. This is certainly manifesting in some poor layer alignment and, I suspect, in occasional collisions between the hot end and the print which are causing belt slippage and subsequent print failure.
I’ve decided to replace the bearings with Mini V delrin wheels from Openbeam as they’re reasonably priced and have a good reputation. The difference in bearing diameter necessitates printing new sliders and, as all the sliders I could find designed for delrin wheels copy the 4 bolt pattern from the linear bearing sliders of the original Kossel design, also new carriages. So it’s a completely new slider/carriage assembly then …
After looking at (and printing) a few slider models, I settled on these double-sided ones for the increased rigidity they’ll provide. The version for Mini V wheels doesn’t come with built-in spacers so I quickly designed some suitable ones - 6mm inside, 7.5mm outside (to accommodate my slightly protruding cable routing). The carriages I chose were a nice simple design which didn’t include belt tensioning or end stop adjusters as both these things are happening elsewhere although I did need to superglue some risers to the top of the carriages at the last minute as they weren’t tall enough to contact the end stops before the slider hit the end stop mounts - so maybe end stop adjusters would have been a useful feature after all.
Once everything was ready I removed the old carriages, fitted the new ones and re-calibrated the printer. The effector is much more solid now and results from the first print indicate that the layer alignment issue is solved. It remains to be seen if the more catastrophic layer alignment failures have also been solved - there’s always the possibility that something else is causing them and the hot end/print collisions are a symptom rather than the cause.
Posted on 28 May 2016