Infill

We received several questions in the comment section of our Kickstarter regarding infill.

Hugues Laliberte:

"@Kudo3d, you said below:
We do not print solid models that has large cross-sectional area because it is very hard to control the bulk shrinkage.
I'm still not very clear on the possibility to use infill. I need strong parts, i cannot print them hollow. So if you say large cross sectional sections will shrink, then it's better to print with 0.2 or 0.4 infill, with a hexagonal pattern like we do for FDM ? Is this possible or not ? I would like you guys to expand on this topic, maybe in the forum. Not all users are printing small figures. You have a large print area, so we need to use it to print large parts too, with dimensional accuracy and solidity."



Peerless Design:

"@kudo and Hughes- I definitely can't be printing completely hollow parts for my business, was the abs test piece that I sent you printed solid hollow or some type of infill? This could be a problem for me.

Albert T

@ Kudo3D, regarding questions posted by @ Peerless Design and @ Hugues Laliberte, I think it may be a good idea to define "large cross-sectional area". How large can a cross-section be before hollowing it out. Furthermore... hollow structure can still have a very thick wall as long as the overall cross-section is still not above the "limit", right? Also, I think infill is difficult for SLA because it does not allow the resin to drain effectively... Can you pioneer a slicer that both allow infill and will automatically create holes / path to drain excessive resin trapped within? :P

The Answer:

It depends mostly on the resin. We have to measure the shrinkage for these low cost resins and then do test printings for solid, larger models. The user can purchase low shrinkage resin from name brands. A large, solid model could require hundreds of milliliters of resin, which can be very expensive.

Albert,
We will definitely take your suggestion into consideration. We just tested our first ABS-like sample last week. This will be an on-going process. Thank you.

Hughes,

If necessary, we add supports inside to resist shrinkage. The infill pattern for FDM requires special software to do it. We will look into the possibility to adapt FDM's software to do this. Thanks.

Peerless Design,

The ABS test was printed solid but that part is small. We were discussing the larger models like the tall statues printed. Thank you!

Doing a bit of research, it seems possible to use partial infill with DLP, at least that's what we see in pictures here:
http://forums.reprap.org/read.php?1,...359#msg-340359
jon@kudo3d was also posting in this thread.

Slic3er.org say they are supporting DLP as well but there is not much details, seems there is an option to export the layers to pictures rather than gcode, i need to check this , i use slic3r for my FDM printer, like it.

I definitely see the need to print larger parts with a partial infill to save on resin costs and weight. And it's probably not a big issue to slice it in a way for the uncured resin to be able to escape for most of the layers.

Thinking of it, partial infill with DLP is great because it does not require more time to print, only less resin, and surely we can create smart infill to improve the strenght/weight ratio. It seems a must-do for DLP.

I believe these guys are using a similar technique to DLP to do just that, albeit at lower resolution, but it's just a matter of time until we have projectors who can achieve this resolution for us DIY:
http://www.3ders.org/articles/201406...-material.html