WIP: Bowden Based Dual Extruder (More Reliable, Too!)

This is for general discussions. Also FAQ can be found here.

Moderator: speedake95

Post Reply
superhornet59
Posts: 60
Joined: Wed Apr 03, 2013 1:58 am

WIP: Bowden Based Dual Extruder (More Reliable, Too!)

Post by superhornet59 » Fri Jul 26, 2013 3:21 am

So, if anyone has been following, I have had 3 full months of systematic malfunctions with the Felix extruder.. and I've had enough, so I've designed and successfully tested a bowden tube based dual extrusion system, which uses the standard Felix hot end (which is actually very elegant, by the way!). Extrusion has been completely reliable and print quality has gone up. So has speed, for that matter.

I'll tell you right off the bad, it's still a work in progress. I've been working on it for a few weeks now, and I think it's high time for a preview of what I'll be releasing soon.

What I HAVE Done

Let's start with the extruder.. I call it the KISStruder (KISS = Keep It Simple, Stupid!) and it lives up to its name. It is very simple, it doesn't even have any springs! How does it handle the (unavoidably) uneven diameter of filament without springs you ask? Simple, it doesn't have a hobbed extruder wheel like the stock Felix, but rather uses an RC car pinion gear with somewhat sharp teeth. These REALLY bite into the filament. Adjusting the tensioner bolt simply makes the gear bite in deeper. I have yet to make this extruder slip, the only way you can mess it up is by overtightening to the point where the motor stalls. By placing the filament closer the motor face, I have also reduced strain on the motor shaft and bearings. Best of all, because it's nowhere near the hot end, it won't slowly warp over time and lose effectiveness.

Pics:
KISStruder.jpg
Extruder.jpg

As for the Felix end, I could write you a textbook laying out the various design goals and features, but the key features are as follows:

*Split Cooling Duct. Most of the air goes towards the heatsinks up top, but some air is directed downwards towards the thread/PEEK. This is to help avoid the hot end softening the carriage, especially when printing at high temperatures such as for ABS.
*Easy to access hot ends. Just undo one bolt and you can pop the hood for a look right from the front.
*Less weight, stiffer carriage, and reduced distance from linear bearing = higher accuracy, even at higher speeds.
*Separation from carriage. Only three front-accessible screws firmly hold the whole shroud to the carriage itself. No longer will you have to reach underneath and have to remove the 4 M3x8 screws that hold the carriage to the linear bearing, should you ever want to test the extruder/hot ends off-printer.

Pics:
Felix End.jpg
Hot End.jpg

Now for:

What I HAVEN'T Done

Due to the nature of my prints, I often print without the cooling fan, so I didn't feel any urgent need to add one in just yet. I'll work on that over the coming while. I'm trying to find a clever way of mounting the fan in the back without interfering too much with the stuff back there... personally I'd like it to be tucked away so you can easily see the nozzle tips, and sticking out in front would defeat that.

Furthermore, while I have printed out a prototype system, I have made minor modifications to the parts (primarily to reduce the diversity of bolt lengths needed, and cut out the need for certain nuts). I will test out the new parts before releasing them.

Also, I have not actually tested out dual extrusion. I have the wiring done and the parts printed except I don't have a second pinion gear, and the hobby stores are sold out so I have to wait a week or so while they order one. Bugger, didn't want to make you guys wait that long, especially because I may be going away for a vacation soon. What I can tell you in the meantime is that single extrusion with the system is working VERY well, I have been running it day and night for a couple of days now and it has performed absolutely flawlessly, not a single jam or anything close. The print quality has definitely gone up as well, but probably more from the improved extruder rather than anything to do with reduced moving mass.

I also plan on putting together a comprehensive BOM and exploded diagrams, so it will be a no-brainer to gather the hardware and assemble it. This project isn't quite finished yet, but I keep hearing about people suffering problems with the extruder and I wanted to tell you guys there is hope on the horizon.
Last edited by superhornet59 on Sat Jul 27, 2013 6:08 am, edited 2 times in total.

seaton
Posts: 291
Joined: Tue May 14, 2013 9:04 am
Location: Bunbury, Western Australia
Contact:

Post by seaton » Fri Jul 26, 2013 4:35 am

I like the simplicity, well done so far! I look forward to seeing this progress.

I really like the way you can remove the heads from the carriage. I'm in the process of adding a small 2W Laser diode to mine so I can so some cutting and engraving and wanted to modularise the head I'll look at how you've done it. Would be nice to standardise so it makes things easier to swap heads etc any chance I can get access to the design files, mainly for the carriage?

Regards,

Stephen...
Stephen...

Felix 2.0 -> Felix 3.0 dual
Simplify3D Slicer, Kisslicer
Have you added your Felix to the Map? http://goo.gl/maps/HajnZ

http://blog.strobotics.com.au

dognotdog
Posts: 181
Joined: Tue Sep 04, 2012 9:22 pm

Post by dognotdog » Fri Jul 26, 2013 8:59 am

Pretty sweet!

How much "slack" does your bowden system have? E.g, when you manually push the filament into the bowden, with the extruder cold, how far can you push it in, compared to no force applied?

superhornet59
Posts: 60
Joined: Wed Apr 03, 2013 1:58 am

Post by superhornet59 » Fri Jul 26, 2013 3:16 pm

Stephen, good idea on the standardization, to avoid CAD-compatibility issues and to allow anyone else who's interested to add a module of their own, I've attached a dimensional drawing of the carriage faceplate for now.
Felix Carriage.JPG
If you need anything else including CAD (SW2013 native) just let me know and I will PM you. I don't want to publicly post incomplete CAD and lead people down the wrong path, my box full of incompatible prototype parts taught me that lesson, ha!

P.S. the laser engraver system sounds AWESOME. I could use that for some projects as well. Would one be able to take the g-code for that and run it via Repetier Host? I noticed in printer settings there is a "CNC Machine" Option.

Dognotdog, I remember you mentioning the slack problem when you first attempted the bowden system, but the thread was long dead and buried. In my experience, I have had zero problems with slack. I mean, don't get me wrong, I can shove some extra filament inside the tube when the nozzle is cold, but I don't think this is actually a problem. I'll explain via this diagram (time to get nerdy!):

Slack Diagram.jpg
For starters let's just say this is in 2D because 3D makes things a little too complicated. If you were to cram as much filament into the bowden tube as possible, it would approximate condition A, where the filament follows the outer edge of the tube. At this point the only way to shove more mm's of filament into the tube is if the same number of mm's come out the other end. At first I printed without retraction (mostly to prevent possible grinding) and it worked perfectly because it was in condition A the whole time. But then I though about what happens during retraction, during that slack phase between A and B. For starters, the pressure at the nozzle would be reduced, which is somewhat good, but in order to do a proper retraction, you would simply have to set the retraction distance to equal to or greater than the difference in arc length from A to B. After retraction, the same length of filament will be pushed back in, and condition A will be reached again, and extrusion continues as normal. The only time you notice the filament is crammed in is after the print, because it continues to 'leak' plastic as the filament decompresses. It's not a big deal though. Now, I could see a problem forming as the shape of the tube changes (as the print head moves) but I don't think it's noticeable when the filament is only 0.25mm smaller in diameter than the tube (I used industrial 2mm ID 4mm OD teflon tubing).

Hysteresis is usually the big problem with filament, but the bowden tubes on my setup are relatively short, so I haven't had any problems.. maybe I just haven't gone fast enough yet, that's all :lol: I was cranking out (decent quality, too) prints at 75 mm/s perimeter and 180 mm/s infill yesterday, the only thing I had to do was increase nozzle temperature to help it flow right. Man this machine is capable of so much, and the extruder was just holding it back, now it's ALIVE! Big thanks to Guillaume for setting up the board to readily accept dual extrusion, that was a really good call!

dognotdog
Posts: 181
Joined: Tue Sep 04, 2012 9:22 pm

Post by dognotdog » Fri Jul 26, 2013 8:41 pm

I had the same 2/4mm teflon tubes. However, my bowdens are about 40cm long, and it shows. The stiffness of the material itself is what troubles me. If the distance to the hot-end is short, then retraction immediately reduces pressure in the hot-end, but when you have a lot of springy filament between the extruder motor and the hot-end, it should follow that one should retract more. Possibly, the stepper could go very fast for this kind of retraction, as it doesn't have to work against the filament.

Re-starting the extrusion is a different thing. Maybe with my latest extruder-tensioner design, I could try things again. My direct-extruder print head does have all the provisions to remove the motors and just screw in some bowdens, but I fear the firmware/slicer software isn't quite there to allow good dual extrusion without A LOT of fiddling. Marlin has this "advance" model, but its not very well documented, and thus impossible to setup right. In addition, the slicer also has settings to control oozing and filament springiness, and getting all this tuned right seems impossible.

But, please do post updates about your progress!

seaton
Posts: 291
Joined: Tue May 14, 2013 9:04 am
Location: Bunbury, Western Australia
Contact:

Post by seaton » Sat Jul 27, 2013 1:32 am

Hi SuperHornet,

I will PM you re the files.

Yes the laster head should in theory work on through Repeiter host. And by setting up a separate printer profile I will be able to automatically set the Z-Axis offset in the profile for laser optimal focus

Currently I'm looking at using the unused 2nd FAN I/O to drive the Laser Drivers TTL so will be using the GCODE that controls that fan.

Workflow (in theory).
1) Load files to be cut into Inkscape
2) generate gcode using the Inkscape lasercutter plugin
3) Replace all gcode that enables/disables the laser with Felix V2 2nd Fan GCode
4) Load into Repeiter host and cut :)

Stephen...
Stephen...

Felix 2.0 -> Felix 3.0 dual
Simplify3D Slicer, Kisslicer
Have you added your Felix to the Map? http://goo.gl/maps/HajnZ

http://blog.strobotics.com.au

superhornet59
Posts: 60
Joined: Wed Apr 03, 2013 1:58 am

Post by superhornet59 » Sun Jul 28, 2013 2:41 pm

Update:

I printed out the latest version of the Felix-end files and ran a test print. I chose something a little tricky to really test how well it can print. Ran it through at 150 microns, about 11 hours to print.
Ford Engine Block Printed.jpg
You can hardly see the individual lines in real life except under the light (typical of black), and this angle really brings them out. The repeatability of the x-axis is quite high, although the y-axis is a bit lacking. Might be due to the weight of my glass bed. The bowden system seems to working as well, if not better, than the OEM setup. Because of the leaky filament situation, before printing I do the following: Return the print head to home, Z +30mm, extrude 10mm, press run, and quickly remove the extruded filament with tweezers. I've also set Cura to do a priming extrude of a few mm, and a two loop brim. With all this, I always have very stable nozzle pressure at the start of the print, because we all know layer 1 is crucial for a good print.

On a side note, check out the zebra banding. It's not as bad as it looks from that angle/lighting, but I've had those bands since I first started printing. Not sure if I had them back when I used to use slic3r (I now use Cura), but it could be g-code related. That or this has something to do with the belts or something mechanical. Any ideas? It shows up even on long straights, but fades after a 20-30mm, so it could be some kind of vibration from changing direction, but it happens pretty equally along both axis.



In any case, the whole Felix end assembly has worked very well, so I'll release that as soon as I have the KISStruder finalized. Now, progress on that is as follows:

*I used a printed t-slot nut with two holes (31mm seperation) to hold the KISStruder to the aluminum extrusion. I designed the t-slot nut so it would receive a 4mm hex nut in each hole, seeing as it has to hold up the weight of the motor and all. At this point I believe that a simple ~3.9mm hole should give plenty of 'bite' for the screws threads to hold things in place, eliminating the need for those two nuts.

*I originally used an 18T pinion for the extruder because I thought it was the smallest.. but it turns out there is a 17T available! The smaller the gear the more mechanical advantage the motor will have, reducing any possible motor stalling and increasing the pushing force (= go faster at lower temps). I've ordered two 17T gears and I will be testing them out to see if they work as well as the 18T. It almost goes without saying that you'll have to adjust the new e-steps per mm to get the correct amount of extrusion. I've always had funky extrusion so I've learned to just adjust flow rate on the fly, but I welcome someone to do a more rigorous scientific (calibration cube printing?) approach.


So, if all goes well with the KISStruder changes, you can expect to see all of the files and supporting documentation released mid-late next week.

Matt

seaton
Posts: 291
Joined: Tue May 14, 2013 9:04 am
Location: Bunbury, Western Australia
Contact:

Post by seaton » Sun Aug 04, 2013 5:41 pm

Here is my current work on the Laser cutter/Engraver head for the Felix that fits on this carriage. The laser diode and controller is from http://www.jtechphotonics.com/

I'm currently finalising the head design, here is is below so far.

The Laser Carriage head is an adaption of Matts Dual Head Carriage to take the Laser Diode and heat sink. The fan and face Plate is probably not needed as the carriage is moving and laser is not on 100% of the time.
X-Axis-Carriage1.png
X-Axis-Carriage-exploded.png
laser1.JPG
lasercarriage1.JPG
laser2.JPG
laser3.JPG
Stephen...

Felix 2.0 -> Felix 3.0 dual
Simplify3D Slicer, Kisslicer
Have you added your Felix to the Map? http://goo.gl/maps/HajnZ

http://blog.strobotics.com.au

Kjetilei
Posts: 334
Joined: Fri Mar 16, 2012 8:26 pm
Location: Stavanger, Norway

Post by Kjetilei » Mon Aug 05, 2013 5:29 pm

Great progress!

Looking forward to see the laser in action.

And I hope you can see the result too after you are finished experimenting with the laser .-) Stay safe an remember to buy eyepatches ,-)

Bachgassenbande
Posts: 132
Joined: Sat Jul 20, 2013 12:50 pm
Location: Würzburg

Post by Bachgassenbande » Fri Aug 09, 2013 8:10 am

Looking forward to see an update for the extruder
If trails do show that is behavies better as the actual extruder this would be a great improvement.
Felix 2.0
E3D Kraken Hotend
3mm Glas bed
LED light bar upgrade

Post Reply