This is a screw driven peristaltic Paste Extruder. It is still experimental, so before you decide to build it please check the following videos to see it in action:
Some pictures of the printing head: https://picasaweb.google.com/ioan.festeu/ReprapPasteExtruder?authuser=0&authkey=Gv1sRgCJnau7ew38qs7AE&feat=directlink
You will find a 3D pdf file attached so you can easily inspect the pump.
Also I have attached a dxf file for the laser cutted acrylic mounting plate for Rapman 3D printers. Sorry... for Makerbots and Mendels you will have to find your solution :)
CAD drawing picture shows in yellow the printable parts. The rest of parts are stock M6 threaded rods, nuts and washers and two inexpensive 606 bearings. The stepper motor is a NEMA17.
For the tubing and pumping elements I used two sets of cheap perfusion kits. The pumping elements (shown in creamy colour) are elastic latex tubes you will find in the kit. Idealy you may use standard peristaltic pump tubes.
The reason I am using two elastic tubes (dual chanel) is because peristaltic pumps suffer from the so called "pulsing". That is, when the screw leaves the tubing the corresponding void (where the tube was pinched) will suck back a little bit the pumped fluid at the outlet hence pulsing. But using two chanels arranged in anti-phase pulsing is reduced to almost zero.
Total parts cost (except the stepper motor) is less than 10 Euros.
I will come back later with a complete parts list and instructions.
NOTICE: I didn't uploaded yet the "pressing pads" (two small parts that press the elastic tube over the screw shaft) because I need to make some minor changes, but don't worry I will post them asap. UPDATED
P.S. If somebody needs the early CAD files let me know. I will gladly send it to you so you can adapt to your machine. I am working in Alibre Design PE and I can't save in other common formats so you must find a way to make the conversion.
P.S. 2 I have uploaded the file "pressing pad". You may want to put some rubbery material between the pad and elastic tube to be sure the screw shaft will completely close the pumping tube but not strangulate it. Otherwise the pump will loose the pressure.
Also I have updated the 3D pdf file.
I have attached a picture of the "perfusion set". Don't know the exact terminology in English, sorry. Some sets also have a Luerlock part connecting the needle and the latex tube. My Luerlock file supports that part. Obviously you can use any kind of support that fits you better.
UPDATE 1: watch my third video (I have listed above).
I will upload asap a new screw rotor design. I am not very happy with the current one since it seems it have some bugs: it creates some extra pressure when the rotor leaves the tube hence altering the low pulsation feature.
UPDATE 2: I have uploaded a new screw rotor design (Screw Rotor New.stl). Screw pitch was decreased from 12mm to 10mm so motor rpm will increase just a little bit. It should perform better than the previous one. Will come back with my own results.
UPDATE 3: Uploaded the file Screw_Rotor_New_Support.stl. Unfortunately this file must be printed with support (soluble PVA, PLA?). However this rotor leaves a smaller footprint on the elastic tubes hence less dead volume (less suck back). Still working for the perfect match to bring pulsation close to zero.
UPDATE 4: Check my photo album: https://picasaweb.google.com/lh/photo/oN2Z_e3g6u7eHZYbbXj2nQ?feat=directlink
It is printed using the part "Screw Rotor New.stl". Pulsation is so small I think is a good print. Just a little bit of adjustment is needed. The trick is to find the perfect match when the helicoid is fading (leaving the contact with the elastic tube)such as the dead volume arising is compensated by the incoming volume of the same chanel. Meantime the other chanel is pumping normaly. And so on. For the perfectionists I promise I will fix this to make it even better. Meantime I am preparing new .stl files for the final version. I need to clean up the bugs in some of the parts (there are plenty) and may be to make the pump smaller and with less nuts and bolts.
About the cheap latex tubes: very short lifetime, losing elasticity. So, go proffesional peristaltic tubing. The pressure will be perhaps around 0,7 bar with those tubing. Now I am waiting for the tubes to be delivered (2-3 weeks). Meantime I will try to cast my own tubing from RTV silicone. Keep you updated.