Consistent air prints

Talk about anything.
Post Reply
masada012
Posts: 10
Joined: Sat Jan 18, 2014 2:23 am

Consistent air prints

Post by masada012 » Sun Dec 14, 2014 3:29 am

I recently purchased a reel of transparent ABS from Octave (having great luck from their other color filament), and I have been using it to print out a Raspberry Pi Gameboy and NES enclosure with great initial results.

However, for certain parts, my printer keeps failing, and ends up air printing at approximately the same layer every time (like the three consecutive prints below - that are supposed to be the top half of the front of the Adafruit PiBoy or PiGRRL).
3Fails (Medium).jpg
3Fails (Medium).jpg (224.45 KiB) Viewed 14247 times
After each failed print, I remove the filament to find feeder gear teeth marks with a strange indentation at the very end of the filament. I assume that this indicates feeder gear slippage, but I don't hear any clicking that other users report.
Filament (Medium).jpg
Filament (Medium).jpg (186.14 KiB) Viewed 14247 times
Additionally, taking a look at a side view of the borosilicate build plate (with purple glue stick) I'm using, I find that the initial test extrusion line looks a little rougher/bumpier than usual (although I'm not sure if it's just because the filament is transparent or not - as maybe it's just harder to spot with opaque filaments). I also find that the final layer where the print fails ends up stringy as shown below.
SideView (Medium).jpg
SideView (Medium).jpg (175.5 KiB) Viewed 14247 times
When I switch back to other opaque colors of filament from Octave, I stop seeing this issue, and I am guessing it is a problem with the printability of their transparent ABS filament, or something with this particular spool.

My question is, is this a filament related problem, or is there too much back pressure due to my printer being calibrated too low to the build plate (or is it a combination of both - with the melting characteristics of certain filaments just making them more prone to this problem)? I will try re-calibrating my platform height to see if increasing clearance with the nozzle will fix this, but do any of you out there have any ideas of what could be going wrong???

User avatar
DrewPetitclerc
Posts: 581
Joined: Sat Feb 12, 2011 7:39 am
Location: Silicon Valley California
Contact:

Re: Consistent air prints

Post by DrewPetitclerc » Sun Dec 14, 2014 5:26 am

Do you have temp mod on your printer, "NOT ALL ABS IS EQUAL", the clear Octave ABS prints better at a lower temp and your extruder stepper motor gets up to a high temp as it operates and this will lead to the strip-out you are seeing (the big bite) at about the same time of the build, a cooling mod can help (look it up).
If your build plate was too close you would have the strip-out happening immediately.
Clogs don't usually happen at the near exact same layer unless it is a repeated swelling in the diameter of the filament.
Drew Petitclerc
Petitclerc Designs
Owner/Senior Principal Designer, prototype, tooling and test equipment design and 3D printing
http://flash-graphics.deviantart.com/
http://www.thingiverse.com/DrewPetitclerc

pleppik
Posts: 336
Joined: Sun Dec 11, 2011 2:14 pm

Re: Consistent air prints

Post by pleppik » Sun Dec 14, 2014 2:03 pm

The mysterious thing about this is why would you get a clog at roughly the same layer on each print. Normally filament jams are somewhat random, so there is something strange going on.

As Drew said, if the problem is caused by having the build plate calibrated too high, then normally you get a jam immediately, not several layers into the print.

One thing which comes to mind is heat: if the printer is started cold, the extruder motor and other parts warm up at a fairly consistent rate. It may be that your extruder motor is getting hot enough to soften this particular plastic just enough that it shreds instead of grips the filament. That would explain why it jams at about the same point in the print each time.

This is also something which PLA sometimes does in the Up. Transparent ABS and transparent PLA look very similar but don't print the same. You can verify that the plastic you have is transparent ABS by bending a piece of filament in your hand. PLA is much more brittle than ABS, and will snap fairly quickly when you bend it; ABS will bend almost all the way back on itself before breaking.

mb20music
Posts: 375
Joined: Thu Feb 14, 2013 1:35 am
Location: USA

Re: Consistent air prints

Post by mb20music » Sun Dec 14, 2014 4:26 pm

pleppik wrote: This is also something which PLA sometimes does in the Up. Transparent ABS and transparent PLA look very similar but don't print the same. You can verify that the plastic you have is transparent ABS by bending a piece of filament in your hand. PLA is much more brittle than ABS, and will snap fairly quickly when you bend it; ABS will bend almost all the way back on itself before breaking.
He stated he purchased the transparent filament from Octave and Octave doesn't sell transparent PLA, only ABS so this wouldn't be the case.

masada012
Posts: 10
Joined: Sat Jan 18, 2014 2:23 am

Re: Consistent air prints

Post by masada012 » Mon Dec 15, 2014 1:09 am

I'm using Octave transparent ABS, but just to be sure I have also created a mason jar full of ABS glue using the failed prints, and they completely melt in acetone. So I'm positive that I'm working with ABS. I'm baffled how the printer keeps failing around the same point, and my only theory is that the point where yesterday's print kept failing was where the printer was transitioning from printing a large flat surface to print thin walls, which I imagine might raise extruder temp because of the rapid movement. My only other guess is that ambient temperature and conditions (which are pretty constant) are affecting the prints.

Like Drew suggested I broke out my temperature switch (which had been collecting dust, as I have been using a two setting Afinia and Octave temp switch with no problems until now), and tried printing the ABS at 215, 220, 229, and 250 degrees. Strangely, all of the attempts (except the one printed at 220 with my enclosure door wide open) ended with the printer air printing while printing the raft (failing even earlier than yesterday - and at pretty much the same point again???).
RaftFail (Medium).jpg
RaftFail (Medium).jpg (161.07 KiB) Viewed 14203 times
Every time the print fails, I notice these tiny stringy flecks stuck to the print (this behavior is the same as yesterday). Has anyone seen this happen before? Is this just a common symptom when the extruder gear chews into the filament?
StringyBits (Medium).jpg
StringyBits (Medium).jpg (144.91 KiB) Viewed 14203 times
220C (Large).jpg
220C (Large).jpg (200.89 KiB) Viewed 14203 times
I know that Drew has many extruder cooling mods on Thingiverse, but all of them seem to require me to buy an air compressor. So far I have only been able to find this one cooling mod, that doesn't require more equipment (except for a fan), but am skeptical as to how effective it is. I may eventually invest in such a solution (if I plan on using more of this reel or actually printing PLA on this machine), but are there other, simpler extruder cooling mods that I am missing?

caesar
Posts: 64
Joined: Sat Feb 22, 2014 1:32 am
Location: Romania

Re: Consistent air prints

Post by caesar » Mon Dec 15, 2014 11:17 am

Your material may indeed be ABS but because it is transparent, material properties can be completely different from other ABS's.
From pics I would say that its glass transition point is actually much lower so that it softens faster. This means that the hotend jams because of the drag caused by this material adhering to the heatbrake walls. Because it is already soft, the teeth of the extruder gear are eating into the material, causing your material flow to stop completely.

This transparent ABS that melts completely in acetone (as you mentioned) may have all the bad parts from both ABS and PLA: shrinking like ABS and prematurely melting like PLA. It is a nightmare and personally I wouldn't loose my time with it. Try a lot of fans to cool the extruder motor and the surroundings and good as possible.
Maybe have a blower over the print as well, keep doors opened and hope that it doesn't shrink.

If you absolutely need to print transparent, look into other transparent materials that print well.
(like XT copoliester)

User avatar
DrewPetitclerc
Posts: 581
Joined: Sat Feb 12, 2011 7:39 am
Location: Silicon Valley California
Contact:

Re: Consistent air prints

Post by DrewPetitclerc » Mon Dec 15, 2014 7:14 pm

Why does you signature now quote me as being cheap?
Drew Petitclerc
Petitclerc Designs
Owner/Senior Principal Designer, prototype, tooling and test equipment design and 3D printing
http://flash-graphics.deviantart.com/
http://www.thingiverse.com/DrewPetitclerc

caesar
Posts: 64
Joined: Sat Feb 22, 2014 1:32 am
Location: Romania

Re: Consistent air prints

Post by caesar » Mon Dec 15, 2014 7:52 pm

Sorry Drew, I copied Roller's statement about his drew for a cheap and reliable powder printer.

The emphasis is on reliable though ;)

User avatar
JuliaDee
Posts: 959
Joined: Sun May 06, 2012 10:00 pm
Location: Connecticut
Contact:

Re: Consistent air prints

Post by JuliaDee » Tue Dec 16, 2014 5:46 am

This is really a long shot, but maybe worth taking a look at. I recently had a very similar issue - air printing on a printer that had been working reliably for months of heavy printing. Extruded fine into free air, but would fail just like yours, with a bite out of the filament, after printing the first 6mm or so in height of my print. The culprit was a worn-out feed bearing!
IMG_7869.JPG
IMG_7869.JPG (96.07 KiB) Viewed 14151 times

ming
Posts: 194
Joined: Wed Mar 12, 2014 2:06 am
Location: Georgia USA

Re: Consistent air prints

Post by ming » Tue Dec 16, 2014 1:46 pm

where are the balls :)
Dream@night / Holdit@sameday

User avatar
DrewPetitclerc
Posts: 581
Joined: Sat Feb 12, 2011 7:39 am
Location: Silicon Valley California
Contact:

Re: Consistent air prints

Post by DrewPetitclerc » Tue Dec 16, 2014 5:05 pm

Oh, yeah I think I forgot to mention that in the past couple of years of printing I have replaced this bearing about 5 times due to the same failure conditions.
I have a few extras I keep on hand because the conditions and stress applied to these little bearings is way past the load limits.
McMaster-Carr, 7804K125, Miniature High-Precision Stainless Steel Ball Bearing - ABEC-5, Double Shielded, for 3 mm Shaft Diameter, 7 mm OD

I'm working on a new design using the new "Printrbot" dual geared extruder combined with the "Recreus" extruder barrel.

Regards
Drew
Drew Petitclerc
Petitclerc Designs
Owner/Senior Principal Designer, prototype, tooling and test equipment design and 3D printing
http://flash-graphics.deviantart.com/
http://www.thingiverse.com/DrewPetitclerc

caesar
Posts: 64
Joined: Sat Feb 22, 2014 1:32 am
Location: Romania

Re: Consistent air prints

Post by caesar » Wed Dec 17, 2014 9:23 am

Wow, thanks for your input Julia. I didn't see that one, probably because my Mini is maintly used for testing materials and that is not too often either.
At first I thought it was the motor bearing but after seeing the size understood that it is the idler that helps pushing on the filament.

masada012
Posts: 10
Joined: Sat Jan 18, 2014 2:23 am

Re: Consistent air prints

Post by masada012 » Tue May 05, 2015 3:38 am

I know that this post is from way back, and since the original post I've just sort of ignored the problem and worked with other filaments (with decent results), but still feel that the issue identified by Julia may still be the culprit (maybe I've just been putting off the inevitable).

One really basic question, however. How do I access the feed bearing? I've disassembled/re-assembled the extruder head numerous times now, but don't remember finding any ball bearing component that can be swapped out. Can anyone tell me where this is located as it seems that it is just a matter of time before this thing will eventually fail, and I sense that mine is on its last leg.

User avatar
JuliaDee
Posts: 959
Joined: Sun May 06, 2012 10:00 pm
Location: Connecticut
Contact:

Re: Consistent air prints

Post by JuliaDee » Tue May 05, 2015 3:55 am

Sorry, I don't have a photo of the stock mechanism handy, but here's Drew's spring-loaded feeder showing the bearing. In the stock feeder it's in the nylon piece rather than on a pivoting metal arm, but in the same basic place, next to the drive gear with the filament in between the two.

Image

masada012
Posts: 10
Joined: Sat Jan 18, 2014 2:23 am

Re: Consistent air prints

Post by masada012 » Tue May 05, 2015 11:03 am

Got it! Thank you so much! It was right under my nose the hole time. I will take your advice and try to take a closer look at it and will invest in a whole bunch of these little guys. Thanks again!

Post Reply