Posts Tagged ‘ bowden

Building the C-Bot 3D printer: Part 30 : Switching from Bowden to Direct Drive

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The original design for the C-Bot by Carl Feniak had the printer setup with a Bowden extruder: The stepper pushing the filament to the hotend sat off to the side of the printer, thus removing mass from the XY/hotend gantry:  The idea is that if there is less moving mass, you can print faster with fewer artifacts (like “ringing” or “ghosting”).  For comparison, my Makerbot Replicator1 (or say, an Ultimaker) is ‘direct-drive’: Its extruder sits directly on the XY gantry pulling filament into the hotend.  This is what I had experience with when I started building the C-Bot, but the idea of learning something new (the Bowden setup) was interesting to me, so I went with it.

Fast-forward to now:  Not a fan of the Bowden setup, at least when used within the specs of my printer design:  I have a E3D-v6 Volcano nozzle (I’ve used .6mm & 1.0mm nozzles) on my bot, and that coupled with the Bowden design have had some quality issues I’ve been unable to overcome despite hours (days…) of test printing.  Specifically “blobs\zits” & stringing.  My guess is, simply too much pressure builds up in the (long) Bowden tube during an extrude move, so when the print goes to do a retraction, a blob still shoots out and gums-up the print, or strings out during movement.  Have not been happy with this behavior, and have been unable to remove it entirely.  Have greatly reduced it, but it’s always there… lurking…

And during this tuning process I came to the realization that a Bowden doesn’t really help things when you’re using a Volcano nozzle:  The benefit of the Bowden, again, is that it removes moving mass from the hotend, allowing you to print at faster speeds.  But with a Volcano, you actually end up printing at much lower speeds, just a greatly increased volume\flowrate.  Here’s some maths:

  • My Replicator1, with a .4mm nozzle, printing at 200 microns (‘medium res’ for that nozzle), at 120mm/sec, has a flowrate of 9.6 mm3/sec (mm cubed/sec).
  • The C-Bot, with a 1mm Volcano nozzle, printing at 500 microns (‘medium res’ for that nozzle) at 45mm/sec has a flowrate of 22.5 mm3/sec.

The C-bot printing at a little over 1/3 the speed of the Rep1, but over 2x faster print times overall (based on the flowrate).  And when you’re printing that slow, I personally don’t feel the moving mass has such a big effect.

On the flipside, if you’re building one of these bots and running a .4mm nozzle, the Bowden is probably ok:  Smaller nozzle, less pressure, less blobs & stringing.  But since I’ve never actually used one on my bot, this is only a guess.

Time goes by…

After some discussion on the Forms (starting on this page, where you can also find the files for download, and my detailed comments on its design), Carl created a new “beta” direct-drive system.  Which is just amazing of him to do, so again, many thanks Carl!  I printed them out on my rep1, spent an afternoon installing them, and what a difference!

The firs pic shows off the new direct-drive design, and a calibration print of two cylinders:  Zero stringing between them.  With the Bowden, it would look like a spider could live in there.

The 2nd print is of a 3dBenchy, with no cleanup: Almost no stringing or blobs.  Both prints used the .6mm Volcano nozzle.

For both of these, I’m using the same Simplify3D profiles as before, I just dropped the retraction from the 5ish-mm to 1mm.  So much more accurate!  Currently in the process of tuning them even more.

I also modified the rear-plate to accept the 40mm fan mount & duct as designed by trublu832 on OpenBuilds, and you can find his files here on Thingiverse:  No more dual fans, just one ducted one.

As of this post, Carl has released a new version of the parts I have yet to print, but I plan to soon.

But overall, if you plan to build one of these printers and use an Volcano nozzle, I’d highly recommend using this new hotend design.


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Building the C-Bot 3D printer: Part 2 : Extruder Assembly

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I chose a E3D-v6 Volcano as my printer head of choice:   Since the volume of my new printer will be so big, I need a nozzle that can keep up.  I’ve never used any of their products before, but have read many good things.  Purchased a ’12v, 1,75mm, Eruption – Full Hotend (Bowden)’ kit from Filastruder.  I should note they included surplus mounting hardware (washers, bolts, crimp-tubes, etc).  While I didn’t need them, I always appreciate the extras (including gummy-bears).

It happened to be one of the first things to show up, so that’s why it get’s blogged about first 😉

Links:

Notes on the build process:

The E3d-v6 Assembly Guide is well written:  I really only got hung up on the thermistor wiring:  When cutting and installing the ‘glass-fiber sleeving’, the ends constantly fray:  I found it quite difficult to get the thermistor + it’s sleeving shoved into the small hole on the heat-block successfully with the frayed ends: I had to enlist a sewing needle from my wife to aid shoving the ends in.  Later, installing the ferrule’s (crimp-tubing) proved even more difficult, since they wouldn’t want to slide over the frayed sleeving.  I persevered, but it was a huge time suck involving very tiny things my fingers didn’t like to grip.

The only other (very minor) issue was that the screws used to hold the cooling fan in were slightly too long: They’re sticking out a couple extra mm, I just couldn’t get them screwed in the whole way without stripping their heads.  If I get really OCD I may cut a bit off the end with my Dremel.

Overall, it took me around 2 hours, but I was really taking my time, and constantly getting up to get tools since I did it in my living room instead of my workshop, and was babysitting multiple prints going on my Rep1…

The final result:

e3d-v6_volcano  Beautiful!

Must remember to do the “Final Tightening” stage before my first print.


 

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