The Extruder

I've been working on the extruder design this week.  I ordered a "MK8" type Bowden extruder from eBay last month, but the mounting bracket doesn't quite fit my motors.  I was on the fence about whether to use the extruder as-is, or print one and just salvage the small metal parts (spring, hob gear, and so forth) anyway, so that settled it for me.

A typical Bowden extruder consists of a few things: You've got a motor, which turns a hob gear.  The hob gear turns against the filament and pulls/pushes it through.  An idler pulley steadies the filament on the other side.  A tensioner keeps the pulley firmly against the filament. The tensioner is a V shape with a pivot in the middle, a spring pushing on one side, and the pulley on the other.  If the filament isn't under enough pressure, it will just slip, so you want to push it firmly against the hob gear.  Then you've got a Bowden fitting which guides the filament into the Bowden tube which takes it to the hot end.

I started by printing MaonTEC's extruder design from http://www.thingiverse.com/thing:1055201.  I tried to assemble it using the hardware I had, but it needed a few adjustments:

The screw that forms the pivot on the tensioner was longer than what I had.  I used an M3 screw that I threaded in from the back so it could never fall out, even if the nut came loose.

The M3 screws I had to mount everything to the motor were longer than what it was designed for, so I had to make the body a bit thicker to account for that.  I also modified it for mounting on the side of a 1 inch aluminum extrusion.

It was originally designed to use three of the four mounting holes on the motor, but in the end I only had room to use two without the heads of the bolts getting in the way.  That should be ok because I'm going to mount it so that those two are on the top and the weight of the motor will be pushing down against where the other two would have been anyway.

I also added flanges around the spring endpoints that keep the spring nestled in place so there's no chance of it popping out.  And I filled in some areas to make it printable without supports.

My goal here is just to get a working extruder. I can make incremental improvements on it later.  I think I can call this one done for now.