Well it's basic physics. ABS expands quite a bit when heated to 200C
or higher. Then you lay it down in a layer and it cools to room temp
shrinking quite a bit. Now, you print a layer on top and it does the
same thing, thus trying to break the bond between the two layers, an/
or curl up the bottom layer at the ends. It's built in stress for each
layer and the longer the thread or part, the more shrinkage and stress
built in. Keeping a heated chamber is a false sense of hope. So,
rather than letting it cool to room temp, it's maybe 80C. Well 200+C
to 80C is still over a 100C temp swing and certainly enough to build
the same interlayer stress. SO when the part cools to room temp
(because we cannot keep it in a heated box), you will actually hear
the cracks forming from across the room.
This same effect happend even in injection molded parts. Why do you
think the Z arms on the Replicators warped from HBP heat? The answer
is the injection molding process left built in stress in the part and
when given an outside force such as a temperature swing, the plastic
attempt to releave the stress to bend into a new shape.
You either have to build with a material(PLA) that has less thermal
stress built in, or temper each build in a heated chamber over a long
period of time. The temps required to do that would be near 200C, thus
why the chamber on the bot can't do anything usefull for you. It might
prevent cold draft related stress issues, but won't fix the "built in"
stress of ABS. Plus, as I stated, the extra heat may cause molded
parts of the bot to crack or warp which is a very bad idea. They too
have built in stress and we don't need to find out how much.
On Jan 9, 11:51 am, Bill Culverhouse <
bill.culverho...@gmail.com>
wrote:
> I've printed a good bit in ABS and PLA, and I would say switching to PLA
> would solve the splitting shown. PLA will still "lift" at corners,
> especially
> on large solid/high density infill items, resulting in curved bottomed
> prints.
>
> But I don't get splitting like this with PLA. I used to see it all the time
> on ABS prints.
>
> Printing hollow/very low infill might help if you still must print with ABS.
>
> b
>
>
>
> On Wed, Jan 9, 2013 at 11:36 AM, Jason <
zen.w...@gmail.com> wrote:
> > Unfortunately, I had this problem, and still do. I spent several weeks
> > discussing it here on the Google Group and really didn't get it completely
> > solved.
>
> > I've added a hood and plexiglass windows to the bot, but that didn't help
> > much. However, if I move the bot to a large room with little activity, it
> > works better. But that isn't an option for me most of the time.
>
> > The absolute most helpful trick that worked for me is to l*ower the
> > filament diameter* in Print-O-Matic for every print. I lower it down to
> > 1.78mm, and that forces each individual layer to stick together stronger.
> > It definitely helps, but I still can't print medium to large objects like
> > the one you showed.
>
> > You could always go the route that Kris Kortwright took, and completely
> > smother your bot in foam:
> >
https://plus.google.com/photos/117228107982719398401/albums/581446688...