Update: Changed layout significantly, added filament feed hole
Update: Added groovemount for jhead, added derivation info
Update: Added arcol mount option
Update: Changed idler screw holes to M3's
Update: Added 1mm radius to base of worm gear cause grub screw was causing it to crack (on my print)
Update: changed the layout of the idler tension screw holder in the body (screw holes were a bit too tight and the sub for the bolt went back to far). Added a quick release to the top of the idler screw mechanism.
Update: forgot to rotate extruder bodies before upload
Update: modified extruder body, fillament feeder hole moved, filament hole widened at top, new idler mount holes. New idler design.
So i've completed a rather annoying redesign in freecad so i can change the base layout quickly.
I have printed this and it does work however, i've not used it to print any objects yet so be prepared for it to fall apart, chew your printer to pieces and eat your household pet! It is most definitely a work in progress and treat it as such. The gearing ratio on this machine is variable depending on the gear you use (you can also create your own gear set from the code - this is quite simple, see below), but with the standard gears will vary between 1:15 - 1:18 (the standard Greg's accessible is around 1:4 or 1:5 from memory), so prepare for a really heavily geared down extruder (is it a good or bad thing? wont know until i do some prints). Its a little noisier then normal geared extruders. Currently designed around the jhead hotend (as in the top that extends into the extruder), im not sure what other hotends have similar dimensions but if yours doesnt fit or you know the differences in way i can easily understand, im happy to design a fitting for it.
All STL's are repaired prior to being uploaded.
How to build this:
You will need the following "bits"
2 of M3x50 - Idler tensioner bolts
2 of M3 Springs of appropriate size (or rubber grommets).
2 of M4x?? - for mounting on your carriage/hotend (if you have a gregs extruder currently, the same bolts should surfice)
2 of M3x10 - stepper motor mounting screws (replace with whatever suits you really).
3 of 608z (or similar) 8mm bearings.
1 of idler bearing mount bolt as used on most Greg's and derivatives (optional)
2 of M3x30 - for groovemount option
You will need to print the following:
Worm Extruder - Tensioner.stl
wormonly.stl (SEE NOTE ABOUT WORM GEAR)
and one of the gearonly stl's (15, 16, 17 or 18 teeth, for a 1:15-1:18 gearing ration), i suggest the 16 or 17 for now (or print them all and see which one you like!).
Put the thing together in the same way you would put together a Gregs accessible extruder, leaving the stepper motor till last. Stepper motor only uses 2 mount holes (for now).
NOTE ABOUT THE WORM
The worm has a big circle at the bottom, this is there simply for printing purposes and can be removed post-print (it may not actually be required). The worm should also print just fine with no support (though, make sure your using a reasonably newish version of slic3r - one that prints perimeters from the inside outward).
You can print the Worm Extruder - Idler Bolt.stl if you wish (its just a simple plastic replacement for the metal bit thats in most extruders, i found it worked ok)
You can also print the "Worm Extruder....Spacer....stl" file, you might find this works better for you if you have a Gregs or Wades hobbed bolt as its sized to move the hobbing to the right location in this extruder.
Creating your own gears - pull down my git repo (see below), go into the directory, FromOpenScad/syvwlch-worm and edit the makefile, at the top of the makefile there is two lines:
Changing these will change the worm/toothed gear and next you type "make", this should produce two stls in the "stls" directory called "wormonly-TEETH-RADIUS.stl" and "gearonly-TEETH-RADIUS.stl" where TEETH and RADIUS are the values you put in the makefile (these are the two most important values for changing the gears. You can edit other values by opening up worm-gears.scad and modifying the variables at the top of the file.
Originally, all the steppers I use are Rattm's but recently i stumbled onto a smaller motor called a vexta c4041-9012 (seen on this page http://www.duke.edu/web/isis/gessler/topics/steppers.htm). You can see the motor in one of the pics I've attached, its got about half the size and torque of a rattm. I bought it simply to see if it will drive this extruder so one of my first todos is to attach that motor (when i can get the gear off it which is proving a tedious task)
Figure out how to get 3 motor mount holes going.
- Add design work for alternative hotends.
I originally decided I wanted to do this for no good reason i can remember and spent quite some time with the brilliant openscad libraries generating STL's, importing them into freecad so I could come up with a (rather complex and large) design for a worm gear that could print and attach to a stepper - this was all in vane as the worm prints quite well without modification or support and standing up.
Once i'd completed it, I decided I might as well print the rest of the parts, hook it up and see what happens. I expected it to rip itself to pieces in several ways - I printed the body with zero infill and the gears/idler with 50% infill. I half expected the lack of any substance to the extruder body would tear the idler mount straight off when i tightened the idler, i also expected the worm would tear the teeth off the toothed gear and/or the worm would break off the shaft of the stepper. None of these things happened, in fact it extruded very well on my 0.35mm jhead hotend. You can also see in some of the pics where i've not changed the brim settings after printing the worm (5mm brim) and so the gears have lots of little thin chunks of brim hanging off them from where the worm gear shredded them (nice way of removing brim from a print!).
The original files for this GPL'd object exist under https://github.com/takigama/pjrun/tree/master/WormScrewExtruder and https://github.com/takigama/pjrun/tree/master/FromOpenScad/syvwlch-worm
The body and idler are done entirely in freecad, the worm and gears are done entirely in openscad. The openscad components are dependent on syvwlch's worm library (https://github.com/syvwlch/Thingiverse-Projects and http://www.thingiverse.com/thing:8821), the general layout of the body takes queues from many of the Greg's Accessible+derivatives extruders (See http://www.thingiverse.com/thing:8252).