Modified BMG Extruder

thingiverse

This is my modified version of the BMG dual geared extruder. This project came about because my current single geared extruder became worn and was not pushing the filament consistantly through the extruder. I decided to buy one of the BMG clones to see what it could do. Upon inspection of this extruder I found that the lever under spring tention was difficult to open for filament replacement and that by changing the location of the pivot point I could cut the spring pressure required in half. This allows me to use a weeker spring and makes operation of the lever much easier. While I was at it I replaced the Bowden tube retainer with my favorite retainer which does not mar or chew up the tubing. I also extended the drive shaft in order to provide visual indicator of extruder movement. Although one may use all of the original parts, if the visual indicator is desired, a new 50 tooth gear and longer shaft are needed (see picture comparing gears). Such small teeth can be difficult to build, so I ended up by "exagerating" the tooth profile to give me what I wanted. I used PETG for the gear and printed it at 20mm/s and ground flats on the 5mm metal shaft to accommodate the extruder gear set screw. The original spring wire is about 1mm thick while my replacement spring wire is 0.60mm (see picture comparing springs). I've also included a matching tension knob and indicator hat. For anyone wanting true 3:1 gearing, I've included a 51 toothed gear. The extruder's filament input side has very little strain on it so the tubing is just a friction (4mm) fit. Mounting holes are cleared with a 3.2mm bit and recessed head holes with a 5.5mm bit. The 5mm rod is 39mm long, the 3mm gear rod is 20mm long, the 3mm hinge rod is 30mm long and the adjuster has 20mm of threads. The mounting bolts are M3 x 35mm cap heads (see picture of hardware). The case was printed with ABS with the gear and red parts with PETG. I resized the parts to 102% to allow for shrinkage. The 50 tooth gear should end up 25.8mm in diameter when printed.