Modify Greg's Extruder for Flexible Material

Introduction: Modify Greg's Extruder for Flexible Material

About: I’m a college student a Purdue University studying Mechanical Engineering Technology. I was originally born in Orange County, CA and moved to Greenwood, IN in 2014. In my free time I enjoy spending time in my …

As 3D printing grows bigger more and more cool materials get released. Ninjaflex is one of those really cool materials. It is really interesting to be able to print things that can be squished and return to their normal shape.

I was lucky enough to receive a spool of it as a gift. However, like many people I tried loading it like regular ABS or PLA plastic and it just jammed everywhere. I soon found that there were a few faults with the Greg's extruder that I have on my Prusa i3v.

  • First of which is that I normally use 1.75mm filament and the hole in Greg's extruder is 3mm, this allowed for too much play and for the material to bunch up.
  • Second was that there was quite a large gap below the hobbed bolt and the feed tube below it.
  • Third I was trying to feed it too quickly.

It was these problems that kept me from being able to extrude the material. After some thought I figured out a very simple and easy modification to allow you to extrude flexible material. Basically we will take advantage of the larger 3mm hole and what we will do is just slide in a PTFE tube to get down to the right diameter and fill the gap. It is fairly simple to do and can be completed in a few hours.

Other benefits of this modification besides being able to print flexible material is your normal ABS or PLA prints will also look a lot nicer. So for a few hours of time and about 10 bucks in tools and materials seems worth it.

Step 1: What You Need


  • 3 inches of 4mm OD & 1.75 - 1.9MM ID PTFE tubing

Here is what I used:


  • 4mm drill bit (make sure it is 4mm and not imperial sized.)

Here is a decent set I have:

  • Dremel or other small rotary tool
  • #115 Dremel bits. (round drum style)

As a note I found the easiest way to cut PTFE to length is with a pair of PVC pipe cutters. Cuts nice and flat and won't pinch the tube like scissors will.

Step 2: Mark and Cut

On my Greg's extruder the distance from where the top of the J head touches to the bottom of the hobbed bolt was exactly 1 inch. So take your PTFE tube and make a mark 1 inch up from either end (that side becomes the bottom). That mark will be where you want the bottom of the notch to be.

Then take you dremel with the #115 bit and slowly start cutting as shown in the picture till you see a little more than half the filament. Please note not to cut the tube with the filament still in it though.

As a note PTFE is sorta slow cutting and gets hot really fast so I'd suggest clamping it in something and cutting a little, then let it cool, and then cut again. Because you don't want to warp or stretch the tube.

Also just out of luck the #115 dremel bit happened to be almost the exact size for the hobbed bolt.

Step 3: Drill & Check Fit

Now the hole in Greg's extruder is 3mm (give or take a little) and the PTFE tube we have is 4mm. So the hole needs to be drilled out to 4mm to fit the tube. Also the idler bearing holder needs to be drilled out at the top to clip the tube into. For the idler you will need to rock the bit up to down a little to cut the whole groove, just take it slow.

Now that the holes have been drilled it is time to slide the tube in and make sure everything lines up correctly. You want the 1 inch portion to be closest to the hotend when installed and you want it flush with the surrounding surface. I also found it is easier to feed the tube in from the bottom rather than the top. Then take your hobbed bolt (or regular bolt) and check the fit of the notch you cut. With the idler off the tube should be perfectly straight with the hobbed bolt in place. If it leans out and is making full contact with the bolt then you need to notch the tube some more. Once you are satisfied with the fit then you can begin to reassemble your extruder.

You can glue the tube into the extruder if you want. However, I did not incase it needed to be replaced and I have had no problems with it moving at all. (probably have around 20hrs of print time with this mod now)

As a note you do still use the idler with a bearing. Only reason mine isn't shown is this is a spare extruder I had.

Step 4: Printing Speeds

Before loading any filament I would suggest tightening the idler and extruding around 100mm empty. The reason for this is to allow the hobbed bolt to cut any material in its way and this way it won't clog your hotend. You will then have to loosen the idler and clean up any shavings before loading filament.

Now that you have your modified extruder it should extrude flexible filament with ease. However, you did still need to extrude at slower speeds as jams are still possible even with this narrow clearance setup.

Extruder speeds will vary on every printer. But for my Makerfarm Prusa i3v with hexagon hotend here are the speeds I used:

Infill - 20mm/s

Inside parameters - 20mm/s

Outside parameters - 15mm/s

First layer - 15mm/s

Also like I said while being able to let you print flexible material this mod also makes nicer prints with ABS and PLA.

Vote and Happy printing!

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