Slic3r suggestion...

I've been using Slic3r and I like it for it's ease of use and features. I would like to see a feature added to help with creating hollow parts, though.

Low density infill helps to reduce weight and material, but there's a limit to how low you can go without having problems bridging over the gaps when laying down the top layers. Making a part hollow is the best solution for low weight, but then there's no support at all for horizontal top layers. I think a good solution would be to create a 'vault' (as in vaulted ceiling) over the empty internal spaces so that the 'roof' is always supported by 45° 'ceilings' (I'm going overboard with the architectural metaphors, I know).

See the attached image of two hollow cubes. The one on the left would never work because the 'roof' has no support. The one on the right has a 45° 'vault' that would provide the needed support with a minimum of added weight and material.

For a simple model like this one, adding a vault is easy enough, but I think it would be cool (and hopefully doable) for Slic3r to have an automatic feature to add such a vault to each internal horizontal surface.

It would also be really cool if it could work in conjunction with the honeycomb infill feature. Imagine a hollow part with a low density honeycomb infill and each honeycomb with a little vault at the top. You could seriously reduce the weight and material used while maintaining good strength (due to the inherent strength of the honeycomb structure) and yet still have good support for the top layer(s). Such a design could be created in the modeling phase, of course, but it would be a real PITA to do it by hand...

Anybody else think this would be a useful feature?

Brian-

Edited 1 time(s). Last edit at 10/24/2012 11:09AM by DGC PartWorks.

+1!! I've had pretty much this idea on my todo list for a while but never got around to implementing/suggesting it.

Could it be implemented by making the perimeter count relative to the height?

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

You can do this by editing the Gcode yourself. Someone wrote an article on it somewhere. haha I know that isnt much help, if I find it then I'll post the link here.

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-Tom

Sniper4395 Wrote:
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> You can do this by editing the Gcode yourself.

OUCH! If I wanted that kind of pain, I could just ram a pencil into my eye!!

"Sniper4395 Wrote:
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> You can do this by editing the Gcode yourself.

OUCH! If I wanted that kind of pain, I could just ram a pencil into my eye!! "

I'm in agreement with the OP.

I Understand what you mean as far as more complicated shapes go, but I have to disagree with your statement that the hollow cube you propose would never work.

It would most definitely work, this is the exact situation where "Bridging" come in.
I know this works because I have been able to print 20mm hollow cubes as test prints with no issues.

as far as making a part hollow to reduce plastic and maintain strength, have a look at this post: reprap.forums Richgain provides some information on how to use Blender to achieve a similar effect.

Jaramaniac Wrote:
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> It would most definitely work, this is the exact
> situation where "Bridging" come in.
> I know this works because I have been able to
> print 20mm hollow cubes as test prints with no
> issues.

If you'd care to pass on more info about this 'bridging' technique I would be happy to learn!

Of Course!

Bridging is essentially the print head, extruding plastic out into open air, from 1 point of built up plastic to the next.

there are a lot of files available on thingiverse to help calibrate this for your printer.

Example

its a combination of getting the correct temperature for the plastic, so that it still extrudes nicely, but will cool shortly after being extruded to prevent it sagging, as well as getting the extruder moving at the right speed and usually (when printing in PLA at least) having a fan blowing across the part to assist with cooling.

Slicer does also have a few settings to adjust to fine tune this as well.

Mind you, Bridging will only work if the print head travels in one direction from the first part of the model, to the second part, to join them, it will not work with a direction change mid way.

I will do a little searching for you, see If i can find some more information.

I would still definitely recommend checking out RichRap's blog as well, he goes into some great detail on calibration.

-Jaramaniac

Thanks for the explanation and the examples. It's good to know that there are techniques for creating unsupported features without always relying on some form of support material. I can still see cases where a vault would be useful, particularly as it would not require any special setup, tools or finely tuned parameters.

So, in thinking further, I wonder if bridging setup changes affect the entire layer where a bridge occurs or if it is confined to the bridge only.

Logically, it would seem to be preferable for such things as temperature changes, speed changes and the use of a cooling fan which may be required for making bridges to only be active when the actual bridge is being printed. When other parts of a layer are being printed, you would want to use the standard printing setup, wouldn't you?

So I guess this is a Slic3r (or similar program) question: when bridges are detected, does the GCode apply the special bridging configuration only to the bridge (and only on layers containing bridges, of course) or does the entire layer get treated as a bridge?