New extruder

The makerbot extruder is very good, but I really like Wade's extruder design which is using a stepper motor to push filament into the hot end. Having a stepper motor will give much more control over the extrusion which should help in combating the ugly plastic strings which are drawn between parts of an objects caused by the extruder leaking some plastic after the motor has stopped; a stepper motor can be reversed very quickly and pull the molten plastic back in.

It sounds simple enough to download Wade's design from thingiverse (here) and print it, but currently I am not able to print the largest part. The reason for this is warping. Any design which is larger than about 4 cm is warping so badly that the chance of it coming loose from the raft is about 80%. For larger objects the chance increases and it is double painful there, because when an object is large it usually takes a long time to print and therefore it may come loose after for instance two hours of printing...  Since my repstrap is different from the standard Mendel design (the horizontal rods from the x-axis are further apart), I am not able to use the design without modifying it a bit anyway. I decided to use the most complicated part of Wade's design and print that in ABS, use some 3mm polystyrene plastic sheet for the motor mount and use aluminium L-shaped profiles to attach it to the x-axis carriage.

The  extruder has several parts:

• The extruder block  - Here I used a modified Wade's extruder block; I will upload it as a derivative to thingiverse later.

• The extruder idler block  - For this I used Nophead's beefed up version from thingiverse.

• A motor mount plate - Made of polystyrene having the same layout as Wade's extruder block for the motor but made a bit larger so that it can be fixed with bolts to the modified extruder block
• A large gear - From Wade's design.
• A small gear - For this I used Nophead's gear with set screw.

• A bolt with a special hobbed part to grip the plastic filament, made using two "pinch wheel worm by drill jigs" using the instructions on the reprap wiki.

• Standard 608 ball bearings
• Aluminium profile and nuts and bolts to keep things together.

The bolt looks like this when inserted thought the extruder block:

The extruder is not ready yet, more information to follow later. I did test how well the hobbed extruder bolt grips the PLA filament (which is much harder than ABS) and it looks very good so far.