Ron's Compact Extruder by raldrich

Last crawled date: 3 years ago

This is not the extruder you're looking for. If you're looking for the extruder referenced in Josef Prusa's i3 design, see http://www.thingiverse.com/thing:24219
A direct drive extruder designed for use with a Minebea geared stepper motor, a Makerbot drive wheel, and a MakerGear GrooveMount (or similar) hot end.
All Electronics is out of the required motor - MPJA has a supply of them at a slightly higher price - http://www.mpja.com/prodinfo.asp?number=18840+MS
From the very beginning with my printer, I've been fighting clearance issues with the extruder, which has prompted me to attempt a long series of different extruder designs. I tried internal (ring) gears, a printed planetary gearbox, and a Legoâ„¢ (!!!) worm gear. None were completely satisfactory.
I was about to break down and spend $33 apiece (plus shipping) on gearbox motors from robotshop.com, when ezmobius linked a Minebea gearbox stepper in IRC which was selling for $6.50 + shipping (Many thanks, ezmobius).
So, here you have my best effort for a compact extruder.
My goals for it are (in order):
1) Torque. It must be able to drive 3mm filament.
    So far, I've only tested it with PLA, but I've had no difficulty
    extruding at average speeds.
2) Reliability. It must never let the filament slip, or lose steps.
    Once I figured out that I needed to reduce the retraction
    speed to 10mm/s, it became quite reliable.
3) Size. It must give me use of the full width of my print bed.
    On the newer of my printers, which was built with an extra
    15mm width in the frame, I've achieved that goal. On the
    older printer, the frame will limit my width at high print
    heights by around 10mm.
4) Ease of setup. I don't like adjusting bolt tension whenever I
    change filament.
    The makerbot drive wheel is designed for use with fixed idler
   tension, and (when tested with other extruder designs)
    allowed me to switch between PLA and ABS filament, with
    .1mm difference in diameter, without having to readjust.
5) Ease of maintenance. I don't like taking an extruder apart to
    clean it.
    The back side of the extruder body is open, so that you can
    clean the teeth of the drive wheel without even loosening
    the idler.
    The filament guide runs close between the idler and drive
    wheel, to reduce the likelihood of jamming the the
    extruder when switching filaments.
After designing it, I found that arcol had started an indiegogo campaign to build drive wheels in various sizes, so I added another goal.
6) It needs to accommodate either the makerbot MK7 drive
    wheel, or the arcol hyena 11x5 drive wheel.
    The current version adds a taper to the lower filament guide, which allows it to be used with either drive wheel.
Motor:
     http://www.eminebea.com/en/product/rotary/steppingmotor/pm/gearbox/pg35l-d48.shtml
    (available at http://www.mpja.com/prodinfo.asp?number=18840+MS , but you'll need a small gear puller or faucet puller to remove the vestigial gear).
Drive wheel:
     http://store.makerbot.com/mk7-drive-gear.html or
     http://www.indiegogo.com/mini-hyena (the 11x5 version).
Two variations are provided: One which fits a compact carriage (45mm in in the x-axis), and another which fits the standard Prusa carriage.
Revisions:
    Fixed the bridges in the carriage belt clips.
    Increased the thickness of the carriage mount.
    Increased the diameter of the igus bushing holes.
    Added an (experimental) pocket for an LM8UU bearing to
        each of the carriage rails. I haven't tested this, and I'm
        not sure if it will work to use only 2 LM8UU on a
        carriage, but it saves plastic - consider yourself
        warned.
    Added bolt holes for a 40mm fan to the carriage.
    Widened the openings in the LM8UU pockets. Hopefully
        it'll now actually be possible to get a bearing into them.
    Moved the filament channel a bit closer to the drive wheel, and tapered the lower filament channel, in order to support arcol's "mini hyena" drive wheel.
    Closed the outside of the extruder body, to prevent it from flexing as the filament is driven.