3d print part crack line start to show up after acetone bath a week later

[sdo]

Hi,

Crack line start to show up after a week on my 3d printed part with acetone bath treatment, have anyone encounter this before? I spend hour
of making the parts look smooth and shiny with acetone bath but crack line start appearing at the layer joins after a week. I am thinking because
the abs contracts when it dry from the acetone bath. Any idea or fixes?

Thanks

[JoeyJoe]

As long as you washed all of the acetone off after with water you should be fine. The layers can separate when it's cooling down too fast when printing.

Do you have the unit sealed so little heat can escape? Heated plate?

[sdo]

The 3d printer is sealed with little heat to escape and have heated plate. What you suggest is wash the acetone off once the part is hard enough after the acetone bath? Could the layer heat during printing cause this issue if its not hot enough to bond the layers?

[CaptainObvious]

Something I've been doing lately with ABS prints is to, after the printing is done, leave the heated bed at 100C, put and insulating material around the part (for example, rolled up tissue paper) and then close the top with a styrofoam sheet. I leave it like that at least 20 minutes then turn off the heated bed and let the whole thing cool down slowly.
I think that should help reduce internal stresses in the printed part so that it would be less likely to delaminate on its own or under load. But it's hardly a scientific approach, maybe someone can suggest a proper annealing procedure for ABS?

[Mjolinor]

If you get some transparent filament and some polarising lenses you will be able to see internal stresses after printing. Using those it should be possible to define an absolute "best way" to treat the printed item.

[CaptainObvious]

If you get some transparent filament and some polarising lenses you will be able to see internal stresses after printing. Using those it should be possible to define an absolute "best way" to treat the printed item.

I don't think that would work in a printed part, the material is not homogeneous enough for the polarization distortion to make much sense.

What I think would be a more practical way would be to print thin, long and relatively tall test pieces, once printed break them along the layer plane and see how much they bend upwards from the shrinking strain; then compare test pieces between straight out of the printer and after keeping them hot for some time and allowing a slow, even cooldown.

[Mjolinor]

I don't think that would work in a printed part, the material is not homogeneous enough for the polarization distortion to make much sense.

What I think would be a more practical way would be to print thin, long and relatively tall test pieces, once printed break them along the layer plane and see how much they bend upwards from the shrinking strain; then compare test pieces between straight out of the printer and after keeping them hot for some time and allowing a slow, even cooldown.

I have to concur with this having bought some and tried it, it doesn't work.

[Geoff]

Hi,

Crack line start to show up after a week on my 3d printed part with acetone bath treatment, have anyone encounter this before? I spend hour
of making the parts look smooth and shiny with acetone bath but crack line start appearing at the layer joins after a week. I am thinking because
the abs contracts when it dry from the acetone bath. Any idea or fixes?

Thanks

More infill is required, that is all, and more shells.

Acetone is not only smoothing it is eating away at the binding and if there is only 1 shell in your model and not alot of infill, there simply isnt enough to bind the layers together.

Infill isn't just important to stop parts sagging or giving them support during prints, it is also to strengthen the bonds between layers. If you say, have a 25% honeycomb fill that is filled on every layer and use 2 shells, you won't get the split when you acetone your parts.

How you print the object also makes a big difference. Printing tall takes longer, but printing say, an LCD panel standing upright will be much more rigid than one printed long ways and flat, as there is less layers binding it together and longer sections to allow binding to split and crack.