Printing Hollow Parts, how?

If I have a part that is, lets say for simplicity, a short hollow box then how would that print? 5 sides I can see as having no issues but how would that sixth side (top section) get printed without it falling in on itself?

I have something I am making that must be hollow on the inside to hold liquid under about 80psi pressure (at most) and trying to glue it I wouldn't trust the glue and supports wouldn't work because no one could get in it to get the pieces out (small orifice on one side).

Edited 1 time(s). Last edit at 08/08/2012 03:38PM by Dark Alchemist.

Two main approaches to printing hollow are:

1. Disable Fill. Usually will produce single perimeter walls. May not work well if you need to bridge the top of the cube.

2. Leave Fill enabled, but set fill to 0%, and increase the bottom/top layer counts to 4+. Also use more perimeter layers 3+.

All this is base on Skein Forge. I do not know the equivalent in Slic3r, but it should be very similar.

Bridge the top? I don't understand as all sides are connected.

Bridging is where filament is stretched over an opening.

In terms of pressure, 80PSI is far from trivial for a plastic container.

Polygonhell Wrote:
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> Bridging is where filament is stretched over an
> opening.
>
> In terms of pressure, 80PSI is far from trivial
> for a plastic container.
Bridging is exactly what will happen when only the edges of each side, in my example, are connected. Nothing is in the middle and that is why it is a hollow box.

Edited 1 time(s). Last edit at 08/08/2012 06:33PM by Dark Alchemist.

What if you print the box balanced on an edge? Create some thin support walls to keep it from falling over, otherwise everything is 45 degree angles. It might be tough to pull off, but would make an interesting experiment.

The part I am making I can't figure out how to make it without it caving in on itself. I am in the modeling stage right now as I am trying to learn a bit more (push myself) in C4D and will take a stab at Freecad but I am worried about the hollow nature.

I wonder if all things hollow need to be injection molded?

Is it too complicated to be printed in 2 parts and welded with acetone?

One of the connecting pieces must be in one piece plus I don't know how many people on Thingiverse would weld it together even if it could be welded together but, alas, it can't be due to the connecting piece that must be in one piece.

Dark Alchemist Wrote:
-------------------------------------------------------
> The part I am making I can't figure out how to
> make it without it caving in on itself. I am in
> the modeling stage right now as I am trying to
> learn a bit more (push myself) in C4D and will
> take a stab at Freecad but I am worried about the
> hollow nature.
>
> I wonder if all things hollow need to be injection
> molded?


I thought injection molding made solid parts as well...I think you mean rotomolding.

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C. Cecil Wrote:
-------------------------------------------------------
> Dark Alchemist Wrote:
> --------------------------------------------------
> -----
> > The part I am making I can't figure out how to
> > make it without it caving in on itself. I am
> in
> > the modeling stage right now as I am trying to
> > learn a bit more (push myself) in C4D and will
> > take a stab at Freecad but I am worried about
> the
> > hollow nature.
> >
> > I wonder if all things hollow need to be
> injection
> > molded?
>
>
> I thought injection molding made solid parts as
> well...I think you mean rotomolding.
Not sure what it was I was watching but some guy was cranking on a handle and the finished product was a whistle (which is, of course, hollow).

I never even heard of rotomolding before but I found this DIY video [www.youtube.com]

so this is a hollow cube? Will anyone ever be able to see the inside?

Bridging can do it depending on the size and if you can't see in then some droopy inner layers won't matter

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Experimenting in 3D in New Zealand

If you print a simple cube with zero infill the top will bridge just fine, assuming your cube isn't too big. The filament can bridge from one side to the other. The first bridging layer will sag somewhat, but should recover within the next two layers just fine.

Also, I would never trust a printed part to 80psi pressure.

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40psi is what I expect and I expect my printed parts to withstand that or back to the drawing board to find out why. 1mm is what I would print at not 2mm to give it the extra strength it needs.

Ummmm...... When making metal containers like gas tanks they test them to 1psi because more than that will destroy them. I think to hold 40psi you would need a printed container about 30mm thick and even then I hope no one you like is anywhere near it when it is pressurized. Compressed air is a tremendously powerful source of energy. I built custom vehicles for years and we would install air suspensions and you could hop the front of a vehicle with a v8 a few inches off the ground with only 100psi.

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I never said this was sealed tight at 40-80psi only it has to handle that much pressure. Every other thing I see made of plastic does so I am not worried in the least. I can go pick one up at Wal-Mart right now that was made in two pieces and glued together so, as I said, no worries about it as long as the horizontal is done better than the average reprap stuff I see now (meaning use 1mm or less where it is smooth for rigidity and strength).

The pressure that a plastic vessel can withstand depends on mainly in the tensile strength of the material and the shape of the vessel.The required " industry standard" for carbonated drinks bottles is 150 PSI and I have tested them to 200 -250 when demonstrating the safety of water rockets (hydraulic test).
If I were to make a printed pressure vessel, particularly if it needed to be non spherical, to arrange it as a multipart design screwed together with sealant or gasket/Orings then hydraulic test to higher than expected working pressure. If it deforms leaks or pops back to the design stage !

TCase

Dark Alchemist Wrote:
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I can go pick one up at
> Wal-Mart right now that was made in two pieces and
> glued together so, as I said, no worries about it
> as long as the horizontal is done better than the
> average reprap stuff I see now (meaning use 1mm or
> less where it is smooth for rigidity and
> strength).

1mm or less what? Also, the plastic probably could withstand 80 psi, if it was injection molded and solvent welded together. The problem is that RepRaps work by laminating layers together, this creates weak points between layers. This is where the failure would be.

Also, if it is not sealed tight, then it won't really be seeing the full 40-80 psi. Likely much much less, depending on the volume capacity of your compressed air source.

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1mm or less layer passes. 2mm is what most print at where you can see the ugliness of the horizontal layers whereas 1mm, or less, it almost looks like it was injection molded.

Dark Alchemist Wrote:
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> 1mm or less layer passes. 2mm is what most print
> at where you can see the ugliness of the
> horizontal layers whereas 1mm, or less, it almost
> looks like it was injection molded.

0.2mm or 0.1mm.

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NewPerfection Wrote:
-------------------------------------------------------
> Dark Alchemist Wrote:
> --------------------------------------------------
> -----
> > 1mm or less layer passes. 2mm is what most
> print
> > at where you can see the ugliness of the
> > horizontal layers whereas 1mm, or less, it
> almost
> > looks like it was injection molded.
>
> 0.2mm or 0.1mm.

Yes, that is what I meant.

Dark Alchemist Wrote:
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> > 0.2mm or 0.1mm.
>
> Yes, that is what I meant.

Ok, that's why I was confused.

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