I came up with this extruder inspired from the compactness of the makerbots Stepstruder. It uses pretty much the same printerbot extruder mount design, just replacing the different parts by one 2-3 plastic parts. It requires a stepstruder MK7 hobbed gear and a spring loaded bearing system of some kind. I used the Minimalistic Mk7 replacement by whosawhatsis.
The motor can be run cool enough to not require a fan, however a fan for the hotend may be required to stop the heat getting to the plastic.
Nema 17 stepper
MK7 stepstruder hobbed gear
Bearing (623 size - 3x10x4mm)
Heavy duty spring (~30x8mm)
2x Linear Bearing (8mm ID, 15mmOD)
1x M3x10mm screw
6x M3x16mm screw
Possible problems & tips on use:
-SPRING TENSION! (you really need a strong spring, so strong that the PLA arm hyolding the bearing flexes a little.
-STEPPER HEAT will melt the filament passing though the gear and damage the extruder where the screws tighten! (Don't run the stepper too hot, you don't need to. My printerboard has the pot set to about 25%)
-Bearing alignment, use the correct size bearing. (The design of the bearing arm by whosawhatsis has the bearing a bit off centre, either edit the file or make sure you use the right size bearing.
-Bearing binds on plastic arm (Make sure you clean up the bearing arm so nothing binds.
-Keep speed under 125mm/m or whatever your hot end allows. (You'll get slippage from the gear and the gear will get plastic all over it)
-Prevent extruder overheating due to nozzle being so close.
- I added some foil tape behind the hot end just incase the heat affects the plastic behind it, haven't had any problems yet with up up 2 hour long prints at 215degC.
- I didn't have the right size spring so used 5 smaller springs stacked together. An M4 screw holds them in place but doesn't tighten, allowing the top spring loaded mechanism to be released for quick filament change.
I have this running at 100mm/min and just printed a 2 hour print no problems, all motors cool to touch.