Airtripper’s Bowden Extruder V3 – Updated Design

By Mark Heywood | December 13, 2012

Airtripper’s Direct Drive Bowden Extruder V3

The Airtripper’s Direct Drive Bowden Extruder is now at version 3 with the design files ready to download from Thingiverse. A lot of work went into the design to improve the usabillity and the look of the extruder. The design is stronger with a much cleaner 3d printed finish, and filament changing is now much easier than before.

The bowden extruder was originally designed to fit the Sumpod 3d printer to replace the bulky MDF extruder housing that was awkward to use. However, the bowden extruder can be used for other 3d printers making use of it’s simple bracket, and the extruder has been popular with the Rostock delta 3d printer. A tube bracket is now availble for attaching to the bowden extruder to help guide the filament from the filament spool. more about that here at Sumpod 3D Printer Filament Handling for Bowden Extruder.

You will find more about this bowden extruder on the following page: Bowden Extruder Upgrade Part 3.

The popularity of The Airtripper’s bowden extruder was boosted when the extruder was included in the development of the awesome Rostock 3D Printer (delta robot 3D printer). To see the bowden extruder in action on the Rostock, watch the youtube clip below.

Bowden extruder V3 Update Details

A number of updates were made to the bowden extruder design with some minor updates on the strut and idler housing.

To get a better fill between perimeters around the screw holes, the rounded ends on the strut have been increased to 10mm in diameter to improve print quality on wider 3d printer settings. A small taper was added to the edge of the idler bearing housing to make it easier to slide the rubber tube over the preloader hook.

The filament drive gear housing has been filled-in to improve overall print quality by minimizing stringing.
Filament guide funnel size increased and angled for (a) a more gentle filament bend around the drive gear and for (b) easier filament threading.
Holes opened up and angled to give the idler preload screws better clearance from the idler housing hooks.
M4 nut for bowden cable (PTFE tube) now drops in to position much easier than before, also, reduced filament snagging when threading into the bowden cable.
Screw column housing lowered and widened at the top to minimize shrinkage and deformation. The M3 screw now drop in without drilling out, although a 25mm screw is now required instead of a 30mm. However, a 30mm screw will fit with a washer so the screw cap does not drop into the recess.
Holes removed from the fixing bracket to improve overall 3d print quality.
The filament in-feed bracket is re-designed for a much cleaner look and is now attached to a screw column for added strength.
A spacer is added so that extra washers are no longer needed.

Bowden Extruder V3 Parts List & Files

Most of the items below can be acquired cheaply from Ebay. The MR105ZZ Ball Bearing is optional but recommended, and the Rubber Diesel Hose can be replaced for coil springs. The M6 nuts, bolts & washers are for attaching the extruder to the Sumpod 3d printer or any other printer with similar fixing arrangement, just decide what length of bolts you need.

Extruder 3D Design Files

All the files for this extruder project are on Thingiverse for download. I’ve Supplied STL files that combine selected 3d objects for printing in one session. This is good for the smaller 3d objects because the printed layers will be given more time to cool. You can download the files from here:

http://www.thingiverse.com/thing:35404

Special Parts

Nema 17 Stepper Motor. Since this extruder is a direct drive type, a powerful stepper motor will be needed. Point your browser to http://reprap.org/wiki/Stepper_motor for a good source of stepper motor information.
Filament Drive Gear. For direct drive extruders, I can only recommend the MK7 drive gear at this point. If this does not work, you probably have Hot End issues. Starting with a tried and tested drive gear will help with your extruder system trouble shooting.

Screws, Nuts & Washers

1 X M3 x 25mm S/S Cap Screw Allen Bolt.
2 X M3 x 30mm S/S Cap Screw Allen Bolt.
2 X M3 x 45mm S/S Cap Screw Allen Bolt.
1 X M3 x 6mm S/S Button Head Allen Bolts.
3 X M3 Stainless Hex Full Nuts.
1 X M4 Stainless Hex Full Nuts.
2 X M3 washers.
2 X M6 S/S Hex Head Bolts.
2 X M6 S/S Flat Form B Washers.
2 X M6 S/S Hex Full Nuts.

Ball Bearings

1 X 608 ZZ [8 x 22 x 7] Roller Skate Ball Bearings.
1 X MR105 ZZ Model Miniature Ball Bearing 5 x 10 x 4mm.

Tube

1 X PTFE Tube 4mm x 2mm.
1 X 1/4″ 6mm id Rubber Diesel Hose Tubing Line.

Printing the Bowden Extruder

Direct Drive Extruder 3D Printed Parts

As a guide for printer set-up, I’ll list some of the settings used to compile the G-code. The toolchain I normally use includes OpenSCAD, Skeinforge, Printrun/Pronterface and Marlin. The settings listed below will be those used in Skeinforge, just the notable settings are included that works for this 3d print. Printing thicker layers and adding extra shells could create gaps in some surface layers, especially around screw holes that are close to a surface edge.

Carve: Layer Height = 0.25
Dimension: Filament Diameter = 1.75
Fill: Extra Shells on Alternating Solid Layers = 2, Extra Shells on Base Layers = 1, Extra Shells on Sparse layer = 1, Infill Solidity (ratio) = 0.25

The STL files should be all you need to print off the extruder successfully, and I’ve provided extra STL files that will allow you to print a pair of selected items or all the items in one go.

3d model images have been uploaded to Thingiverse to help identify which STL files have multiple objects in them. The STL files rendered to images by Thingiverse don’t clearly show the files with multiple 3d objects.

Assembling the Bowden Extruder

The original assembly instructions are still valid for this bowden extruder update and you can find it here: Extruder Upgrade Part 3.

To add to the original instructions

The bowden extruder V3 bill of materials is slightly different from the last version because of a couple of small changes made to the extruder main body. However, all the parts used to assemble previous versions of the extruder will still fit the new version without buying new parts.

As mentioned above (bowden extruder update details), an M3 x 25mm screw is now required for one of the screw posts for attaching the extruder to the stepper motor. However, an M3 x 30mm screw can still be used if a washer is added to the screw before inserting in to the screw column. This will shorten the screw enough to fit the stepper motor body.

Direct Drive Extruder Stepper Motor with Gear, M5 washers and Ball Bearing. Notice the bearing with electrical insulation tape to increase diameter.

The bowden extruder features an axle bearing support for the optional MR105 ZZ ball bearing to spread the load on the stepper motor shaft. Because of variations in 3d printer outputs, it may be necessary to add a bit of extra diameter to the ball bearing. When assembling the bowden extruder, take note of the amount of contact between the ball bearing and the bearing support. If you don’t think there is enough contact, try a piece of electrical insulation tape to add some diameter to the ball bearing. Add as many tape layers as needed to get good contact.

Some types of filament drive gears, after lining them up with the filament on the stepper motor shaft, will leave a gap between the ball bearing and the drive gear. For proper stepper motor shaft support, the ball bearing should be positioned at the end of the shaft. This position can be maintained by adding M5 size washers to fill the gap between the bearing and the filament drive gear.

Airtripper’s Direct Drive Extruder V3 Assembled View from Front	Airtripper’s Direct Drive Extruder V3 Assembled View from Back
Airtripper’s Direct Drive Extruder V3 Fitted without washer on M3 x 25mm screw	Airtripper’s Direct Drive Extruder V3 Fitted with washer on M3 x 30mm screw
Raptor Universal Filament Drive Gear from QU-BD, CNC machined from a brass alloy and shipped with the MBE Extruder.	Airtripper’s Direct Drive Bowden Extruder V3 Fitted to Sumpod 3D Printer

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Thomas December 14, 2012

Hi,

thanks for your great design. Is there a chance to print an exruder body without the holes for a M4 nut for the bowden assembly. What i need is a version with a 4mm hole to tap a m5 (Gewinde) to connect the Tube with a puhfit adapter. I tried to change the scad files but i´m unable to find the right lines in scad to do this by my self. Maybe you can upload a second version that fits for Pushfit fittings.

Kind regards
Thomas B.
1. Mark Heywood Post authorDecember 14, 2012
  
  Thanks for your comment.
  
  The changes required are simple enough to guide you, and it will save you having to wait for me to upload a new revision. So here goes:
  
  The basics:
  Put a hash tag # in front of a line of code to highlight were it is in the 3d model. This will make sure that you have the right line before editing.
  Put two forward slashes // in front of a line of code to disable it, like commenting out.
  
  Now the editing:
  
  Look down the code for the line (about line 258) that reads:
  // Bowden out-feed tube holder
  The few lines of code we need to change are just after this point.
  
  Disable or delete the two lines of code after the line:
  // m4 nut slot
  
  Disable or delete the first line of code after the line:
  // just a hole
  
  Now, to change the hole size you need to edit the first line after:
  // Tube and filament holes
  Change the cylinder radius value to the size you want.
  r=2.25 will produce a hole about 4mm diameter.
  
  And that should be it.
  
  Press F6 to compile, then export to STL.
  
  If you are having difficulties, let me know and I will send you the file.
  
  Mark
  1. AnthonyVH January 7, 2013
    
    Dear Mark,
    
    I’m trying to modify the extruder for a pushfit connector (8mm hole) and followed your guidelines above. However, I’m getting the following error when trying to export to STL: “Object isn’t a valid 2-manifold! Modify your design..” I’m using OpenSCAD 2011.06. Do you have any idea what might be causing this?
  2. AnthonyVH January 7, 2013
    
    Please ignore my previous comment. The error was due to the increased hole diameter being too large & too deep. Increasing the size of the block into which the push-fit connector has to screw and changing the depth of the hole fixed my problem.
    
    Cheers,
    Anthony
    1. Mark Heywood Post authorJanuary 9, 2013
      
      I think M5 or M6 push fit connectors would be better because there is less chance for the filament to snag inside the fitting, and the smaller fittings fit the bowden extruder better with the instructions above.
      As you found out, there was not enough structure to fit an 8mm hole in the bowden extruder design.
      I’m glad you was able to make the modifcation.
      
      Mark
William Stanley December 21, 2012

Hi Mark,
Great new design.
I still have your original extruder, but I’ve just fitted a MK7 drive gear instead of the original Sumpod gear. The effective diameter is larger and this makes getting the filament threaded through quite difficult. Does the new design allow for this; I can’t see it directly in the list of changes.
Regards
William
1. Mark Heywood Post authorDecember 22, 2012
  
  Thanks for your cmment William.
  
  A lot of the changes was made in V2 of the extruder to fit the larger MK7 Drive Gear Pulley. The extruder V3 Builds on that, making it a lot more user friendly.
  
  I have the MK7 Drive Gear Pulley in the extruder version 3 now and the filament curves round it just slightly. The slight curve is useful because the filament and gear pulley have better contact for extra grip.
  
  I would recommend you upgrade to the new extruder design for the improved benefits.
  
  Mark.
Dave Farver January 10, 2013

Hi Mark
I’m looking at converting my CNC router to 3d printer and like your design!
Is it possible to by one? Just printed parts or assembled?
Thanks
Dave
1. Mark Heywood Post authorJanuary 11, 2013
  
  They are currently being sold on ebay, UK and US sites.
  
  Search Airtripper on ebay and you should get the extruders listed.
  
  Mark
MonsterMark February 20, 2013

I am not having any luck with this extruder.

What hot end are you using? Does this design work with ABS?

There appears to be too much pressure for the filament to advance via the direct drive.
1. Mark Heywood Post authorFebruary 20, 2013
  
  For the direct drive extruder to work well you need all the other components to work well also. If the filament is difficult to extrude through the hot end by hand then there is an issue with the hot end.
  Hot ends that require a lot of pressure to extrude will have print quality issues as a result. The flow rate will be inconsistent with delayed start and delayed stop and oozing will be a problem.
  PLA is difficult to extrude for some hot ends because the filament swelling is not handled well. ABS may work better for your hot end and the extruder will work with this material just as well as with PLA filament.
  
  It is recommended that you use at least the MK7 drive gear filament pulley and a high torque stepper motor such as the SY42STH47-1684B (Holding Torque (Kg.cm) 4.4). Having these components will give you the best performance you can expect from a direct drive extruder.
  
  The hot end I’m using is a hacked Mendel Parts V9 clone which is working well enough but still has issues and difficult to assemble.
  
  Mark.
MonsterMark February 20, 2013

Yes, I have the raptor mk7 from QU-BD. I have tried 3 different hot ends. QU-BD, j-head mkIV, and SeeMeCNC’s hot end.
I currently am running a j-head on my prusa with 3mm ABS and its dialed in great!
The SeeMeCNC hot end had the least pressure when manually feed, so I am going to go back and try that again.
1. Mark Heywood Post authorFebruary 20, 2013
  
  I’ve tried the raptor gear pulley from QU-BD and found it was no where near good enough for the job. The teeth are too few and too thick to prevent slipping and the amount of pressure you needed to stop slippage made the stepper motor too weak to push the filament with usable force.
  
  I’ve recently started using the Makerbot MK7 Drive Gear pulley and found it performed far better than the other gears I’ve used.
  
  You can get the MK7 gear pulley from here on ebay
  http://r.ebay.com/j8CNBS
  
  I would recommend you dump the Raptor gear.
  
  Mark
  1. MonsterMark February 21, 2013
    
    Thanks for the feedback. Since I am having trouble getting a 1.75 mm hot end. I am going to try this with 3mm filament. What are your thoughts about that?
    1. Mark Heywood Post authorFebruary 22, 2013
      
      The extruder is not really designed for 3mm filament and 3mm filament works better in a geared extruder.
      I would have to make the extruder bigger for the idler bearing to fit properly to allow the 3mm filament to be guided across the gear pulley without a bending.
      
      I’m designing a 3mm filament extruder to add to my printer to make use of the more reliable 3mm hot ends.
      
      It might be worth trying a sample of ABS 1.75mm filament to see if your hot end works better with that.
      
      Mark
  2. Ivan Lendaric August 15, 2013
    
    Hello, Mark.
    
    I have printed your extruder and now am in search of suitable gear for it. Since you wrote that raptor isnt good enough, will this one do?
    
    http://www.ebay.co.uk/itm/MK7-Drive-Gear-Pulley-for-1-75mm-and-3mm-plastic-filament-For-5mm-axis-Nema17-/271012284234?pt=LH_DefaultDomain_0&hash=item3f1997474a
    1. Mark Heywood Post authorAugust 15, 2013
      
      That is the gear I’m using and it works great for direct drive as long as you are using a high torque stepper motor like the SY42STH47-1684A.
      
      Mark
      1. Ivan Lendaric September 4, 2013
        
        All right. I got the whole system installed (finally), but i am confused how do i need to calibrate direct drive bowden setup that i have with this MK7 gear.
        
        (48 * 16) * (50 / 1) / (10.56 * 3.14159) = 1157.49147
        Is this the correct calculation?
        
        Im asking because im puzzled by the first number which multiplies with microstepping (my extruder is 0.9 degree motor)
      2. Mark Heywood Post authorSeptember 5, 2013
        
        You do not need that formula. You can put in 47.14 as the extruder steps per unit to start with and then calibrate the same as for X and Y axis.
        
        Extrude 100mm of filament and then measure actual extruded length. Use the formula below a couple of times until the calibration looks good.
        
        NewStepsPerUnit = SampleTravelDist / ActualTravelDist x OldStepsPerUnit
        
        Mark
Fernando October 25, 2013

Does this model work with a 5:1 geared stepper such as this:
http://www.phidgets.com/products.php?category=23&product_id=3317_1

I just ordered the motor (from reading about people having issues with direct drive) and commissioned a print of this model to start my first Kossel (wolfstock/berrybot3d, really).

Just wondering if I need to order another standard nema17 until I can print my own modified Airtripper v3 with geared drive mounts. (I’m using 1.75mm filament).
1. Mark Heywood Post authorOctober 25, 2013
  
  Hi Fernando,
  
  There is really no issue with direct drive extruders once they are set up to good specification. My direct drive extruder is pushing 3kg of force which is plenty good enough for a good standard type hot end.
  
  I have a planetary gear stepper motor the same as yours but have done nothing with it so far but I’ve ordered another MK7 drive gear that will be drilled to 8mm to fit.
  
  There is already a modified Airtripper extruder that may fit your planetary stepper motor and here it is:
  http://www.thingiverse.com/thing:140653
  It looks pretty solid and I’ll give a try myself.
  
  Mark
fdsa November 8, 2013

How well will this work with 3mm filament? Assuming I drill out the hole for the filament to pass through.
1. Mark Heywood Post authorNovember 8, 2013
  
  Hi,
  The 3mm filament will require more force to extrude than 1.75mm filament. So whether the extruder will work or not will depend on the stepper motor torque, stepper driver tuning, filament drive gear diameter and hot end.
  
  The MK8 drive gear may be the best choice to get the 3mm filament through the extruder; larger gears might cause the filament to bend too much in the extruder filament guides.
  
  Mark
Adam January 20, 2014

You mention you can substitute coil springs for the diesel hose. What sort of coil springs are these? Also, how did you make the holes in the hose?
1. Mark Heywood Post authorJanuary 21, 2014
  
  I tried springs from cloths pegs, they where very strong, and they worked well enough for tension.
  
  However, using springs makes it very difficult to fit the idler and makes filament changing very awkward.
  
  I recommend using diesel hose because that is what I have tested, but you could use any sort of soft rubber or silicone mat type. The hose provided good idler tension and the idler could be removed easily to change filament.
  
  I drilled the holes in the tube with 3mm metal drill bit, using a dremel and goggles.
  
  Mark