One of the consequences of installing the the slide bearings is increased vibration of the Y-axis belt. This leads to very interesting but disturbing patterns on the printed pieces. From my experience with the Sells Mendel I designed a parametric belt tensioner to manage belt vibration and tension problems.
If you happen to have vibration on the Y-axis belt, just take some bearing fitting your belt width, pick the corresponding screw, washers and nut, enter the parameters into the SCAD file and print this thing two times. It attaches to the bottom threaded rod in the Prusa Mendel and is held in Place by two M3 screws.
Have fun & successful printing!
As I already wrote earlier, the cheap LM8UU linear bearings on the Y-axis already wore out after printing some 2.5kg of PLA and I created some nice slide bearings that attach with zip-ties to replace them. Today the linear ball bearings really broke, so I mounted the new bearings to avoid trouble with the smooth rods. FTW. When the sintered bronze bearings wear out I will try Igus bearings. The X-axis also starts to make noise and rattle,... we'll see.
Chinese filament spindles have a somewhat exotic inner diameter, so none of the standard bearings on Thingiverse work. I made a 608 based filament spindle bearing myself. The 608ZZ ball bearing needs to be put in while still warm. The PLA piece is designed to fit around snugly when it cools. The cylinder for fitting to the bearing is slightly tapered. OpenSCAD file is on Github.
My LM8UU linear bearings broke, due to their overwhelming quality :(
So I got some slide bearings in 8x10x10 and needed to think about a stable way to mount them.
I designed some zip-tied mounting brackets for the slide bearings in OpenSCAD, mounting them later today.
|Finished X-, Y- and Z-axis assembly|
I took several design decisions, differing from Josef Prusa's design which I will describe a little in detail.
I decided to use trapezoidal spindles in 8mm diameter with 1.25mm lift per revolution. The nuts are no ordinary M8 nuts but milled/cut trapezoidal bearings that come with an outer dimension of 17mm (as opposed to 13mm for M8 nuts). So Josef's excellent X-ends are rendered with larger channels for the nuts. I also need to make them longer (higher), but this will happen soon when I replace them.
The motors are mounted with springs from beneath, pulling them into cut felt beds sitting between the motor mounting plate and the stepper motors. This improves precision while giving some mm of space when the extruder misses the endstop and rushes into the build plate.
Stepper uses T2.5 belt with a 12-teeth pulley. The Y-mount bracket has a lower long hole serving as belt tensioning device. The build plate is attached with flush-mounted M3 screws against the moving part. This connection is rigid, eg. no springs. The lower part of the build platform is attached via zip-ties to four LM8UU bearings running on the smooth rods.
As already mentioned the X-ends are customized for the larger 17mm nuts. The X-carriage holds two fans and has an integrated belt-tensioner. The belt is also T2.5 driven by a 12-teeth pulley. While mounting, the motor-side end broke apart and I fixed it with UHU plus acrylit. Works like a charm.
The best about all this: It prints!
Rich wrote a really really good intro on how to get started with Slic3r: