|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!