Orcinus' Build Log (was: Thermistor insanity)

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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby orcinus » Sun Sep 30, 2012 8:22 pm

I'm starting to become painfully aware of how different various PLA filaments can be, even from the same seller.
And no, it's not just the temperature, as most posts would lead you to believe.

I've been using Faberdashery's electric blue PLA (http://www.faberdashery.co.uk/products- ... tric-blue/) yesterday and couldn't, for the life of me, get it to print nicely. The layers are horribly uneven. Okay, maybe not horribly, but very very noticeably, especially at oblique lighting angles. Faberdashery's black, on the other hand, prints awesome and very even, especially if you lower the temps a bit (counter intuitively - most tips i've heard suggest increasing the temperature to get more even flow).

Now, at first, i thought it's a simple matter of lighting and texture. But putting a few test prints side by side, it gets obvious that the more noticeable unevenness is not an artifact of lighting (sorry, don't have a photo right now). Then i thought, maybe it's temperature, and played around a bit. And nope - same deal, regardless of temperature (tried everything from 180C all the way up to 210C).

And then i've noticed something... Faberdashery's black, as well as Ultimachine silver and some other filaments that i've found print really nice and even, all have one common characteristic - they don't break easily. As in, if you make a free air extrusion and bend it, you can bend it nearly 180 degrees 5-6 times before it breaks. In fact, some, like Ultimachine silver, i have to cut with scissors when there's a strand of extrusion left hanging cold from the nozzle. I can bend them and twist them to no end and they simply don't snap or break.

Faberdashery electric blue, on the other hand, as well as Ultimachine white and black, break easily, with a loud SNAP sound. And all of these tend to print unevenly.

I've been thinking what the cause of that correlation might be and so far, my working theory is that the brittle filaments get mangled much more by the hobbed bolt, as they're less elastic (and less plastic). Instead of the teeth digging into the filament and deforming it, chunks of filament break off, clogging the bolt teeth and slipping of the filament during retraction and post-retract extrusion. Sure enough, after using the electric blue for a few hours, i've removed the idler block and the bolt really was pretty clogged up with it.
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby Liberty4Ever » Sun Sep 30, 2012 11:19 pm

Interesting observations!

It sounds like you are encountering some of the material properties that plague the injection molding industry. It's science, but these problems are so complex that they seem more like art than science.

My Theory: The filaments that snap more easily have less cross bonded polymers. Imagine the molecules as long strands of covalently bonded atoms. Cross linking these polymer strands gives a plastic its toughness. The more the filaments tend to stick together, the more force it'll take to break an extruded filament. There is a lot of complicated chemistry (that I don't understand) that determines the physical properties of processed plastic. In injection molds, if the molten plastic is forced through cavities with a high rate of shear, the physical properties of the molded part can be degraded. Mold design isn't as simple as making a mold slightly larger than the finished part, with channels so it can be filled. The flow characteristics of the plastic need to be considered. There's a similar process with 3D printers. I'd guess that the optimal situation would be filament that's uniformly heated, being pushed straight into a smooth walled nozzle. Any steps or discontinuities inside the hot end could result in shear or flow irregularities that might muck up the entire process. It seems reasonable that some plastic filament may extrude well, while another may not, based on subtle differences in the filament. Maybe the average molecular weight is different, or maybe one filament is more cross linked than another? Maybe the different pigments that color the filament change its 3D printing properties.

This seems like one of these problems that is complicated, and we have few viable options to solve the problem. We can experiment with different filaments from different suppliers to see which works best, and we can change the temperature of the extruder. We might be able to change certain aspects of the extruder, such as the size/shape of the drive gear, or the normal force that pushes the drive gear and filament together, but those are difficult parameters to measure and some extruders are more or less amenable to that sort of tweaking. We can share our results with each other so we have some community knowledge and we're not all forced to learn everything for ourselves. But at the end of the day, even the same material from the same supplier may come from a different batch and may be very different.

The free market is a wonderful thing and can help us with complicated problems like this, almost automatically. If we have success with filament from a particular vendor and share that success with others, and they buy from the same vendor, that vendor will succeed and will be more likely to be recommended to those just starting to 3D print. The magic of the free market is that none of us, buyers or sellers, needs to understand why something works, or how it works. We only need to understand that it works. The best solutions to our problems naturally emerge. The free market is smarter than all of us, and that effect is at work with filament, extruders, stepper drivers, 3D printer controllers, heated build platforms, software.... 3D printing has reached critical mass and I'm confident that a lot of the nagging problems will start fixing themselves (more or less). There are many smart people working on many small problems, and the cumulative open source community effect is huge, but even in the cases where the problems are complex and no single person has risen to the challenge of mastering the problem and solving it, selecting random successes and repeating them while discarding random failures will eventually evolve solutions to the most vexing problems.
Apparently, I didn't build that! :-)
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby orcinus » Mon Oct 01, 2012 12:40 am

The hot-end i'm using (Arcol.hu) has a very short melt zone and a relatively long nozzle cavity, which should alleviate most complications caused by differences in the flow (caused by the properties of the polymer). In fact, from what i've understood, the longer-than-usual hole in the nozzle is there, according to the hot-ends constructor, precisely for that reason - to make the flow at the exit as laminar as possible.

Which is why i'm more inclined to think it's a simpler thing - namely variations in pressure caused by the slipping/skipping/clogged filament drive. Although i admit, that's just a guess. So anything is possible.

It just occurred to me it should be somewhat testable. If killing the retract option and printing long objects without many starts and stops (the 20mm single wall square extrusion, perhaps) turns out with neat and even layers, than my guess is quite probably (but still not 100% surely) right.
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby orcinus » Mon Oct 01, 2012 3:34 pm

Only managed to print this before the hotend barrel clogged and i had to dismantle the whole thing:

Image

That's pretty even. I haven't killed retract here, i've only reduced it a little. And there's much less retracts printing this object compared to, say, a herringbone gear, meaning less changes in pressure. But that pretty much is what i've predicted...
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby orcinus » Sun Dec 02, 2012 9:28 pm

Some upgrades...

Image

- 6.35mm ACME rods (going to replace them soon, these are too bendy)
- Greg's extruder w/ herringbone gears (printed on the previously used Wade's)
- LED lighting on the gantry and X-carriage
- two fans (one 40mm on each side, likely to be replaced with more quiet 50mm ones soon)
- matrix keypad controlling the Repetier fw

Image

Coming up next:
- 3/8-12 ACME rods
- dual QU-BD extruders
- Azteeg X3
- tidying up
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby Liberty4Ever » Sun Dec 02, 2012 11:33 pm

That's looking very good. The LED lighting is pimp! :)

Thanks for posting these upgrades and the info on your ongoing continuous process improvements. It's very helpful to see what is working (and not working) for others.

My Hadrons are back in the boxes, awaiting some more time. Too many other concurrent projects! Maybe later this winter... after you guys figure out all of the fiddly little details. :lol:
Apparently, I didn't build that! :-)
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby orcinus » Mon Dec 03, 2012 2:10 am

Believe it or not, the reason for LED lighting wasn't (primarily) pimping.
The lighting in the room i keep the printer in isn't the greatest. Combined with the gantry's shadow, that usually means i can't see a thing while the printer is printing unless i origami-wrangle the desk lamp so it's lighting the printer's bed.

The LED strips, however, do a really nice job of evenly lighting the build area :D
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby kbob » Mon Dec 03, 2012 4:03 pm

orcinus wrote:Believe it or not, the reason for LED lighting wasn't (primarily) pimping.


Last night I received a strip of individually addressable RGB LEDs for the underside of my (laser cutter) gantry. They're not for pimping either; they're for -- um, fine control of color temperature. Yeah, that's it. (-:
Bob
"If you didn't code it, it will never own you." (-:
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby cvoinescu » Mon Dec 03, 2012 5:55 pm

kbob wrote:[...] a strip of individually addressable RGB LEDs for the underside of my (laser cutter) gantry. [...]


If that's not pimping, I don't know what is. However, I could use one of those to test an idea I have (to use multiple images under controlled illumination to make computer vision easier). Addressable LEDs would simplify the wiring and save construction costs. Where did you get yours?
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Re: Orcinus' Build Log (was: Thermistor insanity)

Postby kbob » Mon Dec 03, 2012 10:54 pm

cvoinescu wrote:I could use one of those to test an idea I have (to use multiple images under controlled illumination to make computer vision easier). Addressable LEDs would simplify the wiring and save construction costs. Where did you get yours?


Adafruit. I got these, but they have several styles.

They have several distributors in Europe.
http://www.adafruit.com/distributors/
Bob
"If you didn't code it, it will never own you." (-:
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