At the top the M8 threaded rod is mounted using an axial ball bearing, so it just hangs down from it.
At the lower end it goes through a radial bearing that is mounted from the bottom. The pulley is mounted in a way that the whole screw is tightened slightly, that way it never bends but will always be straight.
I use an axial bearing at the top since the load is the weight of the X assembly plus the tension on the screw, while at the bottom i only use a radial bearing since it mostly has to cope with the pull of the belt and in axial direction only with the tension force.
This popped up a couple of times on the reprap forum.
Often people ask what bearings to use and i am surprised how often the recommendation is LM8UU for linear bearings.
While LM8UU are cheap (at least the low quality ones) and easy to source, they come with some drawbacks. Ballbearings like LM8UU are designed to withstand rather high loads, much higher loads than are usually encountered when building 3D printer. They are also comparably loud and bulky.
For me sinterbronce bearings are a much preferable alternative for most cases.
They are cheap, even the quality stuff, they are silent, small and very easy to use.
Here are a few images on how i use them for linear motion.
As you can see i only use the rather thick walled variation, they don’t deform easily, which makes it much easier to use them.
The images show the use for the X carriage of my Duo Cube printer as well as the use for Z. Depending on load and available space i either use zip ties or counter plates to mount the bearings.
The rendering shows the shape of the mount. It only holds the bearing in the middle and stops it from leaving the mount. Other than that it can rotate rather easily, which makes it super easy to align the bearings.
I have been using this type of mount in various prototypes over the last year and never had any problems, on the contrary, the precision fit is first class, even the small X carriage has no noticable give at all, but runs smooth and easy.
If you want to replace a LM8UU linear ball bearing with it’s more silent, cheaper and less weighty sleave counter part 8x12x12 you canuse this adaptor.
I basically only use sleave bearing for all linear bearings nowadays and for quite a few radial bearing uses as well. The smaller formfactor alone is a huge argument for me.
Since i use an E3D v6 alongside my Merlins for comparison reasons i decided to put a silicone cover over the heater as well. It served me very well on the Merlin.
The design is simpler and has only two parts.
Just fill the silicone in the outer mold and gently press the inner part into the outer until it sits firmly. Silicone will ooze out at the rim.
Even if you use separation agents, chances are high that you need to destroy the outer mold part to extract the cover.
I don’t have much (or more exactly any) experience with Airbrushing, but the first thing i noticed with my new tool was the bad fit for my rather large hands.
A bit of modelling in Cinema 4D and a couple of prototypes remedied the problem quite nicely.
The handle is easy to remove for cleaning.
After i did the cover that you can mold around the Merlin heater block, i wanted to make a sleave that can be put over the heater.
The mold comes in three parts, just drill up the holes to 3mm and assemble the parts with M3 screws to hold them tight. It is strongly recommended to use PTFE spray or other any other separating agent. The resulting sleave has a thickness of 1mm and can be easily ripped.
I recommend printing the mold in high quality to get a smooth surface, the silicone will show every small fault of the print.
Thomas Kramm from Hackerspace FFM created some nice Silicone sleaves for the Merlin hotend. Since he uses different heating elements than I, he uses shorter ones that I currently don’t have, I created an own version of this cover.
It protects against blisters 😉 and will reduce the amount of heat lost during print. With the cover the already printed parts will not be exposed to the heat as much as without and you can be a lot less discriminate with material cooling.
You can find the STL for the mold attached
I used silicone meant for tin molds, it holds up till 450°C and i think it will last quite a while at the <300°C it is used in this case.