Summary

Claystruder 2 is a prototype for paste extrusion that is build around a standard fairly lowcost disposable industrial auger extruder. This design is a testbed and not meant as an elegant design. Read about this extruder on http://unfoldfab.blogspot.be/2012/08/road-to-better-paste-extrusion-episode.html

Instructions

Please read this post on the auger extruder (and comments below) before attempting to build this extruder:
unfoldfab.blogspot.be/2012/08/road-to-better-paste-extrusion-episode.html

Things you need:

-disposable material path (the auger)
-HeadV1 5D.stl
-Auger-Stepper connector.stl
-Nema 17 stepper
-m8 washer (narrow one, OD: 16 mm)
-tape
-luer lock syringe
-Syringe Adapter Head (for example http://www.thingiverse.com/thing:21074)
-2x M3 30mm bolts & nuts
-4x M3 bolts
-luer lock tapered nozzles

I bought my DMP's at dosieren.de (http://www.dosieren.de/en/shop/products/cat/consumables/pr/disposable-feed-screw.html) but you can probably find them close to your place when searching for Techcon or OKI dispensing gear dealers. I used red and black ones and you can also find the steel augers there.

Print out HeadV1 5D.stl, this file has the two halves of the DMP housing. There is a slot halfway the housing where you can insert the washer, this washer prevents the auger from being pushed out of the DMP by the pressure of the material and the tendency of the auger to 'unscrew' from the material being fed. I also cut a small washer from reinforced ptfe sheet so there is less friction and wear on the auger. Insert the DMP in one half and test how loose it sits in the head when closed. Add some tape around the two ends of the T (top and side inlet) that sit inside the housing to make the fitting tight. Otherwise the DMP will wobble a during printing due to small imperfections in the alignment of the stepper and DMP. Now close the two halves with two M3 30mm bolts and nuts.

Print out one Auger-Stepper connector.STL, this is the coupling between stepper and auger. You might need to adjust it for your stepper shaft of file a flat on your stepper. Now push fit this on your stepper shaft. If all is well you can now screw the head on your stepper with 4 M3 bolts. The head was designed for a specific stepper shaft length that was perfect for me until I changed the stepper and the shaft was longer. I fixed this by printing a spacer that you can see in the pictures. You could also use long bolts and some alu tubing on each bolt as spacers. I lost the STL file of that spacer in a burglary.

Now you have a hand held extruder :) For the Rapman I laser cut a new carriage plate (file also lost sorry) that accommodates the extruder including a syringe. The screws that fix the head parts to the steppers went first through the carriage plate, then through the head and in the stepper (from the bottom up). Not very accessible but it was only a prototype to test the feasibility of using DMP augers.

The DMP from dosieren.de came with the nice elbow and extension adapter pieces for fitting a syringe so it sits upright parallel with the head. you can fit whatever type syringe you want, I use 50/60cc medical syringes and the adapter head that I have posted a while ago (http://www.thingiverse.com/thing:21074). But you can use smaller sizes or commercial adapter heads.

Now wire the stepper like you would with any stepper based extruder.

Pressurise the syringe so that it starts feeding the extruder but does not ooze out of the nozzle, that should be the right pressure. Always prime your extruder before using it. Now turn the stepper to check if it prints and find out the RPM.

Claystruder 2, Auger Paste Extruder