About this 3D model

This extruder upgrade for the Replicator 2 replaces the Delrin plunger with a pinch roller. Using the spring specified in the parts list below, this pinch roller provides about 60N of force on the filament, which provides enough driving pressure on the filament, in combination with the stepper drive gear to prevent stripping. Unlike other designs, this one uses a pin style bush on which the pinch arm rotates. This provides a large lower friction surface for the pinch wheel arm to rotate on, and allows the mounting screw to be fully tightened so there is no chance of it working loose. I have extensively tested this design, which has evolved through numerous iterations, and I have also tested several different springs. With the specified spring I can hold the drive gear with my thumb and pull hard on the filament without it stripping, and its done numerous unattended prints with troublesome clear PLA filament - so I can confidently say __it works__. ### UPDATE (Mar 4th 2013) In v7 I have added a filament guide slot to the bottom of the backing plate. I added a spring channel to hold the spring in place and stiffen the backing plate. I redesigned the arm geometry to make it pivot better - compressed and uncompressed. I altered the pin so one side now holds the base plate down against the stepper motor. This extruder upgrade was designed using an ACIS solid in Shark FX/ViaCAD (vc3 file included) so will behave well with Makerware, ReplicatorG and skeinforge. There are also STEP files that can be imported into other CAD programs. Print and source parts, disassemble extruder, upgrade and reassemble, enjoy life 3D printing. ### Now that the Replicator 2 ships with an injection moulded version of this extruder upgrade, much of what I have stated below is moot. I hope the current crop of the Replicator 2 owners run into less problems than we early adopters experienced. ## RATIONALE I have come to the considered view that the design of the Delrin plunger drive arrangement on the MakerBot Replicator 2 is defective. It uses a grub screw seated on a rubber O-ring to provide pressure on the filament to keep it in contact with the drive gear (see picture). The problem with using a rubber elastomer as a spring is that it will tend to seat-in over time, loosing some of its 'springiness' and requiring adjustment. However on the Replicator 2, adjustment of the plunger grub screw also requires the extruder unit to be partially disassembled. Now that the blower fan uses self-tapping screws, it doesn't seem like a good idea to be constantly removing and inserting those screws into plastic threads. More to the point, the amount of spring travel provided by the rubber elastomer is not sufficient to accommodate variations in filament diameter from 1.7mm to 1.8mm and maintain even drive pressure. Unfortunately some rolls of filament contain this degree of variation within the roll. In my experience, clear and white PLA are particularly troublesome. Failure of this plunger mechanism to maintain consistent drive pressure during printing leads to failed prints, wasted filament and printer downtime. The MakerBot website claims that "Replicator 2 has been engineered with the professional designer in mind". I am a professional product designer, and I do not feel that the Replicator 2 Delrin plunger drive arrangement, with these inherent problems, fulfils this usability objective. So I set about to design an upgrade that used parts which were readily available, an upgrade that could be printed reliably, and one that worked as expected. ##PRINTED PARTS I printed the Mk8-Upgrade-Base and Mk8-Upgrade-Arm using my 100 micron ReplicatorG profile thingiverse.com/thing:39050 with the following settings: Infill 100% Layer Height 0.15mm Number of shells 1 Feedrate 80 mm/s Travel Feedrate 150 mm/s Make sure you use a PLA that prints reliably on your machine. However, some more experienced Makerbot operators are recommending printing these parts in Black PLA because black has a higher melting point. Nevertheless, solid parts printed in Black PLA are prone to warping, so I have added ear tabs to hold them down on the build plate better. Seeing these have 100% infill, its not a bad idea to print these bit leaner than you normally would by increasing the filament diameter in Print-O-Matic by +0.03mm. Once printed, ream out the holes on the arm with an M6 and M8 reamer (if you have them) or similarly sized drill bits. This will ensure the parts mate without friction. You can ream out the filament feed hole with the second smallest hex wrench provided with your Replicator 2. There is also a snap-off support on the bottom of the Base that is there to act as a bridge to support the printing of the recessed area. Carefully use a sharp knife to cut this off and use a small flat file to clean the area of any loose strands of filament. There is 0.5mm clearance here so it doesn't need to be perfect. I printed the Mk8-Upgrade-Pin using my 100 micron ReplicatorG p