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An Improved Flexible Filliment Extruder

by piercet, published

An Improved Flexible Filliment Extruder by piercet Dec 15, 2015
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This is an experemental Belted Flexible Filliment extruder which uses the mechanicals from a Bondtech extruder, coupled with a zero backlash belt design and a wade-ish style motor mount, coupled with the feed tube of a lulzbot flexystruder. It should extrude flexible filliment faster, with greater retraction accuracy and less weight than alternatives.

Print Settings

Printer Brand:










80% or better


You will only need support for the fan duct return, Everything else will print without it.


Hardware required:
1 65T plastic (carbide) GT2 pulley w/8mm bore, flanges, set-screw
1 36T aluminum GT2 pulley w/5mm bore, flanges, set-screw
1 GT2 belt, 2mm pitch, 200T, 400mm length, 6mm-with, fiberglass-reinforced, closed-loop (Gates GT2 2mr-88-5 or 2mr-88-3 or equivelent)

1 68mm long M8 bolt
2 M8 washers
2 608 bearings
2x M4 x 55 cap screws
2x M4 nuts for extruder mount
2x M4 Washer
4x M3 10mm SHCS for stepper mount
2x M3 10mm SHCS for Side pod mount
1x M3 14mm SHCS for Side pod
1x M3 8mm for tensioner

1x Bondtech 3.0mm Extruder mechanical kit (http://shop.bondtech.se/ec/kits/bondtech-extruder-v2-30-mechanical-kit.html)

2 M3 x 12mm cap screw for side pod
8 M3 heat set plastic insert for tensioner, and extruder body and side pod
1 M3 thumb screw cap for M3 cap screw
75mm - .25”ODx.125”ID PTFE tube (~2.5”)

3.5mm drillbit (Mcmaster Carr)
6.5mm drillbit (Mcmaster Carr)
13mm drillbit (Mcmaster Carr)
1 hexagon nozzle with a 0.6mm end
2 40mm fans
the stock Lulzbot filliment cooling fan nozzle
12 M3 bolts and washers for the various fan mounts.

Assembly: Print the main body and all sub pieces. Insert all the heat set inserts (2x in the main body, 2x in the side pod pieces, 1x in the tensioner)
Press fit the secondary extruder hobbed wheel shaft ontp the side pod pieces, and install the secondaey wheel. Then Take the main body and use the 6.5mm drill to enlarge the filliment tube. Insert the PTFE tube and then use the smaller 3.2mm drill to widen it out. Findally use the 13mm drill to carve away the PTFE tube in the areas inside the filliment chamber, as seen in the pictures.

THen fit the hobbed wheel to the 8mm bolt along with the bearings and a washer on each side. The pulley acts as the bolt retainer. Install the large pulley on the end of the bolt assembly after it is in the housing. Loosely fit the NEMA 17 motor to the extruder body and with no tension on the tensioner, fit the smaller pulley and the belt to the motor. Next tighten the tensioner and motor mount screws when the belt appears taut.

The hexagon hotend installs as normal. Install the heat set inserts into the extruder fan mount locations, bolt and wire everything up accordingly. This extruder carriage will fit a standard TAZ V notch mount.

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Piercet, will this design work for a lulzbot TAZ 4? I am looking at ways to print TPU with my taz 4, and a flexystruder will run me $300 :(

Yes, but you may have to install a longer Z endstop target bolt. It uses the later taz 5 / taz 6 carriage spacing that moves the extruder nozzle down relative to the X rods, which in turn moves the Z height target up slightly. It shouldn't need to be much different, it's something to be aware of though. Also if your 4 doesn't already have the fan wires, you will need to add those in. INstructions for adding the fan wires can be found in this instruction document https://ohai.lulzbot.com/project/taz4-hexagon-toolhead/accessories/

What do you mean fan wires? Mine does have a fan just like the later models, which can be scaled to speed? Is that what you mean?

You also would need the additional constant velocity barrel cooling fan to make the E3Dv6 work correctly. many of the Taz 4 units have the fillament cooling fan, but not the hotend barrel cooling fan.

Can anyone share their impressions on this design versus a Flexystruder? I'm trying to print filament that's more flexible than Ninja, and run into some extrusion issues (hobbed bolt eating the filament) when there's backpressure or I run the extruder at normal speeds.

I don't know that you will find anyone that has actually printed one aside from myself since the core gears are not inexpensive. For me, I get higher pressure to the nozzle before scour occurs due to the dual wheel configuration, and it seems to work pretty well. I'm actually working on a standard filament version as well that omits the PTFE liner and adds a new Idler configuration. That configuration will most likely be adapted to this one as well once I get it tested. You should see the other one uploaded sometime in the next two weeks. I'm printing the body right now actually, but it has a ways to go for testing and whatnot before I am comfortable releasing it.

As a followup - I'm currently building one of these (I will probably build your Nova Pro too, I grabbed two Bondtech sets) and saw that you had uploaded STPs for the Nova - any chance you could post the STP files here as well? Trying to get STLs into SolidWorks can be a PITA.

Sure, let me dig the parts out and get them posted. Also, i'm about to release a version 2.0 of the Nova pro, so you may want to hold off printing it for a day or two.

Where does the M3x14mm (I assume this guy gets the thumb screw) belong? I am not seeing a location for it.

I think that should be the bolt that holds the idler replacement piece together, and there should be two of them. the other 10mm long ones hold that pod to the side of the main body,

Piercet - Could you please give me the SDP-SI part number you used for the timing belt? I contacted them twice using the numbers you provided in the instructions and they have given me two different part numbers (both wrong sized belts). One way too big and one way too small. So any help you can give would be very appreciated.

The last one I ordered has the following part number printed on it:
SDP A 6R51M088060 and says it is also a Gates GT 2MR88. It's the same size as the one shown in the pictures. The other one also has the same SDP A marking on it.

Your thing details call out a 200 tooth / 400mm long belt. SDP A 6R51M088060 is 88 teeth, for a length of 176mm. When I have that belt on the spec'd pulleys the pulleys interfere by about 1mm. Looking at your pictures you have some pretty decent separation; having some trouble figuring out what the disconnect is.

Well, thats a bit tricky. It's quite possible what I have on there isn't in fact what I think it is. I've ordered things from SDP-SI to try different configurations out, and they have sent me completely identical pulleys for different model numbers in their catalog, so I'm not 100% certain which model is correct. I'll check the belts themselves when I get home tonight. Here's everything I have ordered from them though. Also the 400mm belt may be incorrect. that sounds too long anyways. a Taz bed is only 300mm long and these are much smaller. I also may be using a 24 tooth small pulley from an AO-100 instead of a 36 tooth.

http://shop.sdp-si.com/catalog/product/?id=A_6Z51M065DF0606 2 mm (GT2) Pitch,65 Teeth, 6mm Bore, Brass Insert, Polycarbonate Timing Pulley for 6mm Wide Belt

http://shop.sdp-si.com/catalog/product/?id=A_6Z51M065DF0608 2 mm (GT2) Pitch,65 Teeth, 8mm Bore, Brass Insert, Polycarbonate Timing Pulley for 6mm Wide Belt

http://shop.sdp-si.com/catalog/product/?id=A_6Z51M036DF0605 2 mm (GT2) Pitch,36 Teeth, 5mm Bore, Brass Insert, Polycarbonate Timing Pulley for 6mm Wide Belt

http://shop.sdp-si.com/catalog/product/?id=A_6R51M088060 2 mm (GT2) Pitch, 88 Teeth, 6mm wide Single Sided Neoprene Belt with Fiberglass Cords

Piercet - I printed out the Improved Flexstruder Body 1.0b file and the motor mount section is printing detached from the main section. I checked it in Simplfy3D and it also shows it to be not attached during the print, a gap is shown. I don't see what holds the motor then. Could you look at it for me.

I'll take a look when I get home this evening. Mine all printed just fine in slic3r.

I went and printed it through slic3r and it printed fine then. Don't know why it has problems when printed through the MatterControl or Simplify3D.

Bond tech now sells a kit with a geared stepper motor. Will this motor mount to this design or should I just get the kit you mentioned and use a regular NEMA 17 motor? They mention that they require the geared motor so I am confused.

The belt drive this one uses has more mechanical advantage than the direct off the shaft drive approach that the Bondtech extruder itself requires. A geared stepper should still work, but your response times on retractions might be lower than what they would be otherwise. I'm using a standard Stepper with this.

Thanks for the response. I ordered the parts but plan to use the E3D hot end with it. I'll have to see what modifications I'll have to make.

You would need to deepen the extruder mount hole slightly, that's about it..

I guess this extruder will require calibration of the e-steps right?
Which source did you use for the pulleys?

Yes, it will require an esteps adjustment. The nice thing is though that the bondtech core hobbed gear thingy is machined precisely, so this one and the still in the works standard filliament one will share the same esteps value, and once dialed in properly all of the extruders should theoretically be able to use the same esteps value across the board. I used SDP/SI for the belts and the pulleys

Thanks for the answer! Can you remember the total cost to build it?

Yes, the expensive bit is the bondtech core. That with shipping will run you about $80 unless you are in Europe. The pulleys and belts were about $10, and the other assorted extruder hardware and plastic was another what, $20 or so? Then whatever the stepper motor costs. I just used one of the ones from my large pile of stepper motors.

Hello - we sell trial sizes of NinjaFlex and SemiFlex if you want to try out flexible or get more colors. Thank you. Barbara

Does that mean I get a revenue percentage for letting you advertise here on my work?

How about a free spool? I have lots of colors. I don't know how I could tell which sales came from you but if I could do it I would.