Prusa Compact Extruder rework

Reworked to give 4:1 gear ratio with nozzle as close as possible to bottom x rod and centre of mass as close as possible to x rods.

3D printer parts and enhancements


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    My printer is a Prusa i3 box-frame. However, the printed parts I bought to make it (my first printer) included the x carriage and Wades extruder from here:

    I was pretty happy with this setup until I realised that the nozzle was more than 0.1 mm closer to the bed when positioned at the x center of the bed than it was at the x edges of the bed, making tramming to better than 0.1 mm impossible. Eventually, after trying many things, I determined that the cause of this problem was the flex in the (8 mm) x rods combined with the centre of mass of the heavy Wades extruder being well forward of the x rods and the nozzle also being well forward of the x rods.

    As a result I decided to print a new extruder and mount that would move the nozzle as close as possible to the bottom x rod and also move the center of mass closer to the x rods.

    I use 3 mm filament and I also like to use a light weight (250 gm) stepper on the (non-Bowden) extruder to keep the x carriage total mass down, so I need a reasonably large gear ratio (1:4) and a Mk8 hobbed gear to get enough torque.  Prusa’s compact extruder from the prusa-vanilla repo looked simple and light (M5 rod and 625ZZ bearings) apart from needing a big stepper, so I redesigned it to use a 8 to 32 gear ratio (up from 8 to 24). To move the center of mass as close as possible to the x rods I raised the motor so that it could extend over the top of the x carriage. 

    I did not want to change the x carriage because it is really smooth with no slop, so I designed a mount ( based on to attach my E3D v6 directly to the carriage as high as possible, and offset to keep the centre of mass close to the centre of the carriage in the x direction. I then bolt the extruder to this mount using normal 50 mm spaced groovemount holes on the extruder.

    Note that one of the M4 bolts used to attach the mount to the carriage is also used to hold the hot-end in place.

    I can now tram accurately across the whole
    200x200 build plate.

    I print these parts with Kisslicer medium support (in ABS). 
    The mount is designed to be a tight fit on an E3Dv6 and is probably too tight for an E3Dv5, for which the extruder_cyl2_height parameter needs to be reduced. The mount should be printed with a 0.2 mm layer height.
    I use a 0.26 layer height for the extruder and idler.

    When assembling the extruder, don't tighten the nuts each side of the front-most bearing against the bearing. This is because the bearing ID will be a bit larger than the shaft diameter, so the chances are that the bearing will not be centered exactly on the shaft, causing the shaft to wobble as it rotates. Best to leave the front bearing a bit loose, like the back one has to be. I pack out the shaft where the hobbed gear is with a few layers of aluminium foil before mounting the gear, to center it.

    Sources also available here:

    Materials and methods

    - 1 x MK8 hobbed gear
    - 2 x 625ZZ bearings
    - 1 x 608ZZ bearing
    - 1 x M8 x 25mm grub screw
    - 1 x M5 bolt or threaded rod
    - 2 x M3 40 mm bolts
    - 2 x springs
    - 2 x M3 20 mm bolts
    - 4 x M3 nuts
    - 4 x M4 bolts
    - 4x M4 nuts



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    8947810a53ba7a31c758ebc63cd283ed?default=blank&size=40douglaspb added this to the Legal collection ago
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    Ec18eaac8761b8bda94f9e07fa08177e?default=blank&size=40Cristovão Oliveira added this to the I3 collection ago
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    837d843619492b0b0b6469334ea8c315?default=blank&size=40wbrokow commented ago

    Can you post the "E3d Rework Mount Offset" parts in .step, acis or parasolid format so I could import it into Solidworks. I want to make changes but you can't measure .stl files easily and scad is a major pain.

    319fb9cf0743db1a98ae14f5811bbc77?default=blank&size=40Alan Hyde added this to the Prusa Stuff collection ago
    64f8de1412c9f5cc90662efceba76874?default=blank&size=40xrajox added this to the Prusa i3 collection ago
    24a118e97f707b72aa09a2d16267e6f5?default=blank&size=40Medjay added this to the 3d printer collection ago
    837d843619492b0b0b6469334ea8c315?default=blank&size=40wbrokow commented ago

    basically a spacer, with custom holes to bolt the spacer directly to the carriage . I then mounted

    the extruder directly to the spacer. A bit of measuring , designed it in IronCAD and 3d printed.

    I will send the .stl files to you if you want.

    E7cac3260e725ab195fd2cbe98b44cae?default=blank&size=40spinorkit commented ago

    Thanks wbrokow. I am interested to see how you attached it to the steel x-axis carriage. Could you post some photos a from different angles?

    837d843619492b0b0b6469334ea8c315?default=blank&size=40wbrokow printed this ago
    Carousel thumb extruder
    Printed on:
    Prusa i3
    currently working very well.
    include provisions for use on a real p3steel with steel x-axis carriage & z axis carriage. i had to design adapters and also an x axis switch adapter that does not reduce x travel,
    E7cac3260e725ab195fd2cbe98b44cae?default=blank&size=40spinorkit commented ago

    I have added the stl for the fan duct shown, and the OpenSCAD source. This

    is still a work in progress and the OpenSCAD source is configured a little

    differently from the stl. I have printed the uploaded stl, but not yet the

    one from the OpenSCAD file as currently configured.

    93eae2f48cfc94ce9aad754430632349?default=blank&size=40dansxmods commented ago

    Where did you get the fan duct from

    24ee2577539ae18c4b0af758a9234ad4?default=blank&size=40Tongdam added this to the Extruder collection ago
    E7cac3260e725ab195fd2cbe98b44cae?default=blank&size=40spinorkit published this design ago