Cracking layers after printing. WHYYYY!

[Cymon]

I've got an enclosure. I'm insulating it. I print hot and I print fast and I print in ABS. But no matter what I do when ever I print something over an inch tall I end up with massive cracks, sometimes that don't appear until after I remove the print. For instance the stackable bins ( http://www.thingiverse.com/thing:38194 ) always have to be clamped and glued after printing becasue they're tall and the walls are so thin. Is there anything I can do to prevent this?

[PropellerScience]

Is your filament getting stretched too much maybe? I'm doing all those
things, but I'm not really having separation problems. Maybe printing
"fast" is stretching the filament? I'm usually printing with Sailfish
around 80 mm/sec with ABS just because I'm afraid the heating up part
might not be able to keep up. Maybe try the same print at 80 mm/sec.
My travel speed is 100 mm/sec.

[Joseph Chiu]

Check your filament diameter, it just might be set too high?  Could be the filament...

*duck*

Try printing hot and slow.  Or maybe not quite as hot but still fast.  When you print hot and fast, the high rate of shrinkage can cause delamination.  Also, there is a width-to-thickness ratio that can be tweaked in RepG.  If you go for slightly wider extrusion, you might perhaps get a better smooshing?

On Mon, Dec 17, 2012 at 8:24 AM, Cymon <joeal...@gmail.com> wrote:

I've got an enclosure. I'm insulating it. I print hot and I print fast and I print in ABS. But no matter what I do when ever I print something over an inch tall I end up with massive cracks, sometimes that don't appear until after I remove the print. For instance the stackable bins ( http://www.thingiverse.com/thing:38194 ) always have to be clamped and glued after printing becasue they're tall and the walls are so thin. Is there anything I can do to prevent this?

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[Andrew Plumb]

If it's not filament diameter related, how many shells and what fill percent are you printing with?

Unless I'm printing with 100% fill, I always print with at least one (1) shell.  For larger prints I'll often bump it up to three (3) shells and set fill to somewhere between 0-10% fill, sometimes higher (especially for PLA) when there are large single-layer cap surface areas that need the internal support.

Andrew.

On 2012-12-17, at 11:24 AM, Cymon wrote:

I've got an enclosure. I'm insulating it. I print hot and I print fast and I print in ABS. But no matter what I do when ever I print something over an inch tall I end up with massive cracks, sometimes that don't appear until after I remove the print. For instance the stackable bins ( http://www.thingiverse.com/thing:38194 ) always have to be clamped and glued after printing becasue they're tall and the walls are so thin. Is there anything I can do to prevent this?

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--

"The future is already here.  It's just not very evenly distributed" -- William Gibson

Me: http://clothbot.com/wiki/

[Cymon]

Oh, you know I've checked my filament diameter. In fact I turned it up just a little bit to insure it's spitting out enough plastic. 0.27 layer height, 2 shells, 10% infill, not that these parts are getting much infill. On these ones I was using altshell, so the outer layer was definately going slow enough, but my general feed rate is 120mm/s. I'll try 80 and report back.

[Dan Newman]

On 17 Dec 2012 , at 9:02 AM, Cymon wrote:

> Oh, you know I've checked my filament diameter. In fact I turned it up just
> a little bit to insure it's spitting out enough plastic.

Increasing the diameter causes *less* plastic to be output, not more.
After all, if it thinks the plastic has more volume (larger diameter),
then it will use less of it.

Dan

[Dan Newman]

So, I'm guessing that was just a typo on your part and you decreased the
reported diameter?

Dan

[Lincoln K]

Are you printing more than one object on the plate in the job? I found that I got much better prints when doing one object per job.

Lincoln

[Cymon]

No, that was me being dumb. Trying it the other way next time.

[Jetguy]

I think the real answer here is change the material.

ABS has a known high rate of thermal expansion/contraction. It comes
out of the nozzle hot at 230C and then drops back down to room temp
30C. That change in dimension per layer is huge. This is why objects
curl up the the bed. That thermal stress is built into the very part
you are building, hence the cracks when it cools or layer on, when
mechanically stressed, it cracks in the same weak spots.

PLA has a much lower rate, and thus much less thermal stress is built
into the part. So much so, PLA can be printed on a cold surface and
generally not warp.

Thus comes the printing rules:
If the part is subject to heat (anything around an extruder or heated
bed, possibly even items like motor pulleys)- then it must be ABS
If it's big or has thin walls and must not crack or warp- PLA is the
right choice.
Basically, build small things with ABS as the small size doesn't have
as much stress as a big part (think about railroad tracks, one rail
section, OK, 10 rail sections, need expansion gaps).
Big things are pretty much PLA only.

I personally define small object as it fits on a Cupcake build
platform 100x 100mm. Midsize is the T-O-M 120x 120 and the real limit
of ABS, anything at or larger than 120mm in any dimension should be in
PLA.

Again, we can fight it all day with heated chambers and all kinds of
other shennaigans. It's a fight we'll never win with ABS. If you get
something to print and not crack before it's off the build platform,
the first time it has any stress or temperature change, it's likely to
crack anyway.

[Big-E]

I know this may not help much, but when I suffer from layer seperation, it's usually because my nozzle is too far from the build plate. I print in PLA though.
Just throwing it out there.
 Big-E

[whpthomas]

How stable it your build platform? If there is a bit of play if could be varying the gap between the nozzle and the work piece - I have a Rep 2 and my build plate was a bit sloppy which caused parts to break while trying to remove them. I added a shim under the build plate to make it push up against the latches better so now it is much firmer. This seems to have solved the layer separation problem I experienced early on.

[Z LeHericy]

What temps are you using?

I get cracking and stuff unless i:
1) Run the bot HOT (250 extruder, 140 platform)
2) extrude lots! (high flow rate, thick lines)

-Zeno LeHericy

//((=:Z:=))\\
INVENTIONS
Technologies
zinventions.com

On Mon, Dec 17, 2012 at 5:13 PM, whpthomas <m...@henri.net> wrote:

How stable it your build platform? If there is a bit of play if could be varying the gap between the nozzle and the work piece - I have a Rep 2 and my build plate was a bit sloppy which caused parts to break while trying to remove them. I added a shim under the build plate to make it push up against the latches better so now it is much firmer. This seems to have solved the layer separation problem I experienced early on.

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[Shawn]

With the right precautions and procedures cracking can be minimized if
not eliminated.

I just finished printing the base for Emmett's Blossoming Lamp
(http://www.thingiverse.com/thing:37926) in ABS. It has a very large
surface are on the platform and extends the full printing height. I had
my hood and 3 side panels for the duration of the print (18ish hours).
These prevented stray temperature changes due to airflow inside the
chamber, yet allowed excess heat to escape. Then after printing, I gave
it a good 2 - 4 hours to cool off in the same environment, before I took
the front panel off. This allowed the entire model to cool at a
relatively uniform rate.

Then to take the model off the platform I did NOT pull on it in any way.
Instead I worked a utility knife under the edges. It took some doing
and I had to re-heat the platform to get a temperature difference
between it and the model to make things easier. (after it was at
temperature for a few minutes I set the platform to cool again) But in
the end, I was able to slip the knife under the model until it popped
off on it's own. Pulling on it in any way would have forced
de-lamination of the layers. Side note - this process destroyed the
kapton so you might want to wait on larger projects like this until you
are about to swap out the kapton anyways...

I have this 15cm tall piece sitting on the desk now without any cracks.
We'll see if it stays that way over the next few days.

Shawn

On 12-12-17 06:21 PM, Z LeHericy wrote:
> What temps are you using?
>
> I get cracking and stuff unless i:
> 1) Run the bot HOT (250 extruder, 140 platform)
> 2) extrude lots! (high flow rate, thick lines)
>
> -Zeno LeHericy
>
> //((=:Z:=))\\
> INVENTIONS
> Technologies

> zinventions.com <http://zinventions.com>

>
>
>
> On Mon, Dec 17, 2012 at 5:13 PM, whpthomas <m...@henri.net
> <mailto:m...@henri.net>> wrote:
>
> How stable it your build platform? If there is a bit of play if
> could be varying the gap between the nozzle and the work piece - I
> have a Rep 2 and my build plate was a bit sloppy which caused parts
> to break while trying to remove them. I added a shim under the build
> plate to make it push up against the latches better so now it is
> much firmer. This seems to have solved the layer separation problem
> I experienced early on.
>
> --
>
>
>

> --
>
>

[Shawn]

And now that I went to change the Kapton, I notice scratches in the
aluminium plate that were not there before. Nothing a new layer of
Kapton won't take care of, but there does seem to be a trade-off in any
of the approaches...

[Cymon]

Lower filament, higher temp, slower speed, still cracking. Maybe not as bad this time, but still happening. "Clamp and super glue" has just become a part of the process of making http://www.thingiverse.com/thing:38194 now. I'll try it again even lower, higher, and slower.

[Joseph Chiu]

What is your speed  and fill settings?  I've recently bumped up my fill->extra shells and fill->solid surface thickness (layers), and reduced the speed->perimeter speed by quite a lot to do some 0.1mm prints.  The resulting outer surfaces were *solid*.

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[Big-E]

Just had a thought, is your machine reporting it's temperatures correctly? might want to check with a non-contact thermometer, just to be sure. Maybe a sign of something failing on your Bot?