SoliForum - 3D Printing Community — Cracking on larger objects?

Re: Cracking on larger objects?

2015-03-25T00:07:55Z

It's pretty well established that under similar conditions parts with thicker layer height are in fact stronger - for a mechanical part like the carriage, I'd defer to the side of physical performance over aesthetics. Can you clarify "look pretty awful"??

Oh, and the vertical slots thing is a good idea. I did that on some fridge brackets that were cracking badly, made a heap of difference. Watch out for the new problem of warping leading to nozzle crashes though. It was a fine line for a while prior to the chamber heater.

Re: Cracking on larger objects?

2015-03-25T00:04:34Z

grob wrote:

I had a part do this weeks after it was finished... Just got bumped and went 'pop' one day.
Evidently there's a fair bit of residual stress built up in a large thin-walled part.
Have you tried with a different (perhaps thicker) layer height? What are you running at the moment? It looks pretty fine...

That was 0.1, I'll try 0.3 (aka 0.2963 as per other thread) next.

I printed a couple of Lawsy carriage parts at 0.3 and they look pretty awful, so I'm doing them again at 0.1 (aka 0.09878) to see if there's much difference in fit.

More News As It Happens...

Re: Cracking on larger objects?

2015-03-25T00:04:16Z

I run into this, too, time to time with large prints. The longer the unbroken run, the more stress. If you can edit the model to introduce vertical slots to break up that wall it should help (allows the model to contract before reconnecting at the top of the slot).

Re: Cracking on larger objects?

2015-03-24T23:44:07Z

I had a part do this weeks after it was finished... Just got bumped and went 'pop' one day.
Evidently there's a fair bit of residual stress built up in a large thin-walled part.
Have you tried with a different (perhaps thicker) layer height? What are you running at the moment? It looks pretty fine...

Re: Cracking on larger objects?

2015-03-24T16:20:15Z

The SD4 has an enclosure, the vent fan is disabled (defective from factory), and I let it warm up for almost an hour before starting the print. Since the bed heater is pretty much 100% on to correct for the thick glass, it's really pretty warm in there.

Just measured 50-60C air temperature depending on how close to the bed I measure.

Re: Cracking on larger objects?

2015-03-24T16:16:10Z

That looks more like an enclosure issue to me. With ABS, you want that enclosure toasty while printing.
I had this problem before putting a lid on.

Re: Cracking on larger objects?

2015-03-24T16:12:17Z

Well, it's way better than my first try:

But still not perfect. I'll try the layer height thing next (maybe tomorrow?)

Thanks!

Re: Cracking on larger objects?

2015-03-24T15:11:52Z

Some of that is just the nature of ABS and some of it is caused by improper layer height as I mentioned over in your other post.
Keeping your chamber warm and avoiding quick temp changes will help some also.

Cracking on larger objects?

2015-03-24T11:53:24Z

So I'm printing off the 4-way Nespresso capsule dispenser from http://www.thingiverse.com/thing:601422

And this one came out the best of all, since I've got:
Bed heat up to really 100C
Extrusion calibration
Flow calibration
Glass bed with hairspray

But I'm still getting some stress cracks:

It's not a printing error, because it clearly happened after the layers were laid down, as it pulled them apart.

You can see the crack appear _after_ the area in question has been printed:
http://geekho.com/push/Nespresso_4OXG_2 … 055641.mpg
It's along the far right side, you can see it's OK around 29 seconds and the crack appears around 30 seconds into the movie.

Is this just what you get with large-ish (this part is over 16mm wide (almost 6.5 inches) ABS parts because the material shrinks as it cools and stresses long spans, or am I doing something wrong?

Thanks!

SD4 (enclosed)
Glass bed at (really) 100C with hairspray
Stock hot-end at 215C
Octave filament