Summary

Based on many other usable extruders but tweaked to be used with an 8mm ID Hobbed pulley mounted on a 50mm X 8MM hex bolt. Works well with PLA or ABS 3mm filament.
I don't use a herringbone gear because that would mean complete dissassembly to get to the filament. In my design the Nylock nut on the back side can be removed and the large gear with the hobbed pulley can be removed very easily for clearing/cleaning after a "spinout"

Instructions

Designed in house at Van-Isle-Rapid-Prototyping after many iterations this is the easiest and most reliable extruder I have ever used. The design is meant to make it extremely easy to:

Change color in the middle of a print by "pausing" your LCD panel.
Clear a jam
Overall Build Time very low.

There are two fans as well as a 5mm LED light connected to the D9 12volt outputs from a RAMPS board. One fan cools the barrel of the J-Head hot end and the other cools the stepper motor.

VIRP-V3 EXTRUDER ASSY
Parts List:
Vitamins: QTY
M3 nylock nut 1
M3 washer 6
M3 x 6mm grub screw 1
M3 x 10mm SH screw 4
M3 x 16mm SH screw 2
M3 x 20mm SH screw 2
M3 x 30mm SH screw 1
M3 x 35mm SH screw 1
M8 Nylocking nut 1
M8 washer 4
M8 x 50mm Hex Bolt 1
M8 x 28mm threaded rod 1
608zz brgs 3
Limit Switch 1
J-Head MK-IV B Hot-end 1
12v Brushless 40mm Fan 2
40mm Heatsink 1
5mm LED+470ohm res 1
JST 10 wire quick plug 1
JST 2 wire quick plug 1
Ty-wraps small 5
Nema-17 Stepper Mtr 1
Fold Back Binder Clip 1

Tools Required:
Drill
Standard wiring and soldering tools
M2.5 Allan wrench
3mm tap
3mm drill bit
3.3mm drill bit
5 mm drill bit

Assembly Instructions
Front side is considered the side that the gears are installed on
This extruder has a carriage assy that is setup for 50mm wide linear 8mm rod otherwise just use screw holes provided
Support material is already incorporated into design
Using this gear set the stepper steps per unit for extruder should be set to around 470

Remove support material from VIRP-V3 Extruder MB (Main Body)(Fig. 1)
Tap 3mm holes in
a. VIRP-V3 Extruder MB
i. Front side of hot end retaining screws (2 places) only tap half depth
ii. R/H Extruder carriage attachment screws (2 Places) under stepper motor
Drill 3mm holes in
a. VIRP-V2 Extruder MB
i. Back side Hot-end retaining screw holes(1/2 way)
b. Limit switch
i. 2 holes
c. Belt Clamp-INF
i. 2 holes
d. Small Extruder Gear-INF Grub screw hole
Drill 3.3mm (tolerance) holes
a. VIRP-V2 Extruder MB
i. L/H side @ Limit switch mount holes
Drill 5mm Hole in Small Extruder Gear-INF Shaft hole
Insert M8x28mm threaded rod into 608zz brg snap into place on EXT BRG Clamp-INF
Grind or file a flat spot on stepper shaft @ the base(not reqd if your stepper is a D-Cut shaft)
Cut off center terminal of limit switch
Feed Limit Switch wires through channels
Install Pre-Built J-Head (w/wiring 60cm for resistor 40cm for thermistor)using (1) M3x30mm SH screw + washer from the back side & 1 M3 x 35mm through fan mount hole from backside
Install 5mm LED with resistor(470ohm mount on the neg(shorter) leg)/wires (30cm length) Cement in place
Neatly ty-wrap wires up-between mtr and drive housing
Install Nema-17 Stepper Motor using (4) M3x10mm SH screws + washers placing wire exit at the side
Solder all wires to JST10 and JST2 plugs following wiring diagram
Build up Large extruder gear/hobbed pulley assy
a. Insert M8x50 hex bolt(grind or file a flat at the thread/smooth transition area for grub screw seat on the shank) through Large Extruder gear
b. Stack (4) M8 washers onto bolt against large printed gear
c. Install 608zz brg
d. Install and tighten hobbed pulley with grub farthest from large pulley, run a piece of 3mm filament through extruder assy to ensure proper alignment.
Install Large extruder gear/hobbed pulley assy into VIRP-V2 Extruder MB
Install 608zz brg into back side(for alignment)
Install M3 nylock nut into Small Extruder Gear-INF(I recommend you run a 3mm bolt through the nylock first just to break it in)
Install M3x6mm grub screw into Small Extruder Gear-INF
Install Small Extruder Gear-INF onto Stepper shaft, tighten grub into flat spot
Mesh gears so there is virtually no backlash, rotate gears to ensure no hard spots, tighten outer two screw on mtr.
Remove Large gear assy
Tighten inner two motor screws
Install Large gear assy
Install M8 Nylocking nut on large gear assy do not overtighten. Gears should still turn easily
Install 40mm heatsink on top of stepper motor (glue or double sided tape)
Install 40mm fan onto heatsink using M3 x 16mm screws in diametrically opposed holes

VIRP Version 3 Geared Extruder