Currently this only works with 1.75mm Filament but I will make a 3mm version soon. I needed an extruder that could do the following three things. Work with Ninjaflex Connect to a PTFE tube for a Bowden configuration Be driven by a Geared Stepper Motor I couldn't find anything that did all three so I decided to make my own. It is a simple design. It is not difficult to make or use. So far it just works. I am very happy with it. See the Instructions for more details. As I mentioned in the Description I designed this extruder because none of the existing extruders out there did what I needed. My first need was to be able to print Ninjaflex. So I copied the main mechanical idea from the FlexyStruder that was designed for the TAZ 3D printer. The main idea behind it is that the Filament never completely leaves the PTFE tube. There is just a small hole on the side of the tube for the gear to push the filament. This makes it so the Ninjaflex is constantly being held into place by the PTFE tube. If you want to know more here is a link to a site that details how to make a FlexyStruder for the TAZ Printers. http://fabsterdam.com/3dprinting/building-a-flexystruder/ So I knew this design would work with ninjaflex. Now I needed to find a design that would connect to my Geared Stepper motors. Let me briefly explain what these are for those who don't know. Geared Stepper motors have a mechanical gearbox attached to the stepper motor. It acts like a car transmission to gear down the motor. This will give the little motor a LOT more power but at the cost of speed. These Gear boxes essentially replace the wade Gear. Moving on. I found a simple extruder that connects to these geared motors. Here is the one I used. http://www.thingiverse.com/thing:706210 I combined the designs and came up with my own FlexyBowden Extruder for Geared Motors Right now I just have text instructions and pictures from when I assembled my 1.75mm version. Later when I design/build 3mm version I will record a video. For now here are the instructions. Read them carefully before you begin or you will make mistakes. a small length of PTFE Tube 2x Brass Bowden connectors 1x 3m Screw at least 16mm long. (Could be longer. Could also be a thumb screw.) 1x 3m nut 2x or 3x Screws 3Mx25mm (for mounting the motor) 2x or 3x washers for 3m screws. (Optional but recommended) 1x Geared Stepper Motor A 5/32 Drill bit Thin Razor Blade Sharpie (Optional) Print the piece using a layer height between .1 and .2 mm. I used .14 and it worked very well. I suggest you print it with the main tube standing straight up. Just like it is shown in the Second Picture with all the parts you will need. With your fingers take the Drill Bit and work it through the long hole. This Drill bit size is intentionally smaller than the PTFE tube. The goal is to get the tube to have a snug fit with no wiggle. So don't go crazy with the drill bit. With your fingers twist the Brass Bowden Connectors into both ends. You do this to make sure they can fit and to make it easy to see how deep into the block the connectors will go. Be careful not to strip out the threading. If you do you will need to reprint the main block. Remove both of the Bowden connectors. Hold your Geared Stepper Motor in place in the block. Look through the hole where the tube will go and make sure the gear teeth on your drive gear line up with the hole. Make adjustments as necessary. Do this now because you will not get a better chance later. Cut one end of the PTFE tube so it is flat. You don't want it to be angled at all. Push the flat end of PTFE tube all the way through the block. The flat end of the Tube should be very near the exiting surface of the block. It should cover some of the threads from the Bowden connector. Carefully screw in the Bowden connector again. You should see it push the PTFE tube back out a little as you go. Again be very careful not to strip out the threads. At this point you should have one Bowden connector in place and the PTFE Tube should be firmly pressed against it inside the block. Take a good look at the pictures to help you understand this next part. Use a Sharpie to color the Tube inside the middle of the block. The Big round hole where the Drive Gear will eventually go. Then use the Sharpie to mark the tube on the outside of the block. Try to get the mark as close to the block as possible. Then pull the tube back out of the block about 7 mm. Read this carefully. You will make two cuts here. Cut the tube where you marked your line that indicates the edge of the block. Hold your Bowden connector up to the tube to measure the length of its threads. Cut the tube again. Make sure the cut is as flat as possible. Use the flat end of the drill bit to push the tube back into the block. It should stop moving when it rests against the first Bowden connector. If you look into the hole you should see the tube end at the same place where the threads stop inside the hole. See the pictures. Carefully screw in the second Bowden connector. If you did everything correctly then the PTFE tube should be getting held into place on both ends by the Bowden connectors. It shouldn't be able to slide around in either direction. You should also be able to see the sharpie markings line up perfectly inside the block. Use a thin razor blade to cut a hole in the side of the PTFE tube. Cut from one side then cut from the other. You do not need to cut all of the exposed tube. Look at the pictures again. You will see that I left some of the tube there in place. Next we need to get the pressure screw and nut into place. Slide the 3m nut down into the slot. If it doesn't slide down on its own then you can use the 3m screw to push it into place. Then thread the screw through the hole and nut. You should see it begin to push on the PTFE tube. Back the screw out just enough so it doesn't push pressure on the tube. All set. Attach your Geared stepper motor to the block and you are done. I strongly suggest you use a filament filter/cleaner with a sponge and mineral oil (Baby Oil works as well.) This will help keep the inside of your PTFE tubing lubricated. Here is a link to the kind I use. http://www.thingiverse.com/thing:497764 When you are loading your filaments you will want to slowly apply pressure by tightening the pressure screw. Ninja Flex is special. You don't want to smash it. You want it to be held just barely tight enough for it to move. Don't make it too tight or you will smash it flat and it will jam. UPDATE 9/9/2015 I had my first failure with this extruder. I have added photos for you to see. My first attempts with NinjaFlex were a success. Then I moved on to test several other filament types. Then I tried to come back to NinjaFlex. That is when it failed. I took it apart and found the problem was caused when I used the other filaments. I ended up tightening the pressure screw a little too much and it damaged the PTFE tube in two ways. First it bent the tube a little then it pushed the tube so it started to rub against the gear teeth. Now the exiting hole for the filament is a little more narrow so the NinjaFlex is getting stuck. I am going to just replace the tube. The moral of the story is that this design may not be able to switch back and forth between NinjaFlex and other Filaments. However I will keep testing. Please feel free to ask questions.