hollow objects ?? printing top and bottom though they are not supposed to be their...

[Chris Taylor Jr]

I just got a makerbot replicator mini. $300 with 8 rolls of filament. I am thrilled with it. so far its working flawlessly near 24/7 for the last week :-)

anyway I am finally starting to diddle around with 3ds to make my own stuff.

Mostly rocket airframe components.

anyway made some simple things to test scale fit precision etc.. and am having a wee problem.

I made 3 parts. a small tube section. a "3d skin" to put on that tube section and a matching Nose cone.

the tube prints fine. Just the tube. but the tube skin prints with a top and bottom even though it SHOWS without either in the software (but shows the top and bottom in the preview)

what am I doing wrong? how do I make it prints just the wall no top and bottom as those are not even in the file the maker software is "adding" them once it does its thing when you click print.

suggestions?

[Jetguy]

This requires a basic understanding of how the slicer reads your STL and makes decisions.

Remember that STL is a very simple point cloud format. Basically it contains coordinate points that represent a wire frame mesh of your object and information on how those points connect.

As such, if you make a single wall cylinder, that is technically a solid object cylinder even if you did not intend it to be.

If you leave off the top and bottom walls of the cylinder, that is an invalid model for 3D printing because it is not manifold/watertight.

In order to make a hollow cylinder, you must make BOTH an external and internal wall, with a known thickness, and those walls must "face" the correct direction. Finally, there still must be roof and floor walls that connect the inner and outer walls and they too must face the correct direction.

Basically, you must draw EXACTLY what you intend and leave no room for errant interpretation by a slicer.

This is because Infill is assumed to be the manifold space between 2 outward facing shells or walls (technically the same shell if we are talking true manifold).

Also note that this determination is made layer per layer. Depending on how complex the sharp was, you can have faults that lead to the slicer interpreting one thing on a layer VS what you intended.

This is along the same lines as Boolean joining 2 objects. In essence, it's the same thing and same problem. If you fail to remove the invalid geometry where the objects overlap, then the slicer has NO IDEA what the heck you meant. It sees shells facing the wrong way, it has no idea what is proper infill, what geometry should be ignored, should be followed, and so forth.

Bottom line is create proper manifold CAD and leave the guesswork out the slicer so there is only one way to interpret your STL file.

[Jetguy]

http://www.shapeways.com/tutorials/creating-hollow-objects

Tip: you can mostly ignore the escape hole last section in that guide for FDM printing.

http://www.sculpteo.com/en/tutorial/prepare-your-model-3d-printing-solidworks/

https://support.makerbot.com/learn/makerbot-desktop-software/printing-tips/shells-and-infill_12722

http://www.3dartistonline.com/news/2011/12/how-to-make-a-model-for-3d-printing/

Good explanation here on Boolean objects as well as making hollow http://homeautomationguru.com/designing-3d-parts-with-123d-design/

Good explanation of flipped faces and CAD Shells http://www.makerbot.com/blog/2011/07/22/google-sketchup-design-tip-fix-flipped-faces

Also a great tutorial on shells and Boolean.

https://www.quora.com/Why-cant-3D-printers-print-non-manifold-and-inverted-normal-designs

[Chris Taylor Jr]

That is a bunch of greek to me from a software pov but... i think intellectually i understand what you are trying to tell me.

I was confused why did the tube work but the star tube not work. I used the tube command to make the tube while i used a shape command and then extruded it to make the star tube. If i am understanding this right gcreate got around this with the vase command process but since i cant use simplify3d mine is not working with that "trick"

If i understand right i am sending a 3d shape that is 2d and therefore invalid so the slicers tries to "complete" the shape into 3d "closing the top and bottom to make it a sealed object.

At first i was like but i want an open object and then it hit me sure but the walls need to be 3d not 2d then it will be hollow in spacial frames but "complete" three dimensionally as a model!.

Ie i need to give the shape thickness and an outside inside face versus the backside of the outside face of my 2d plane folded in 3d space.

I think i grasp that. The tube worked because i used the tube command so 3ds "did" all of that for me.

So. Do you think i have the basic idea right? If no clarify if yes how do i fix it. I am at work right now i will read links later tonight after work.

I appreciate any help i can get. Here is a video i made before work this morning.

https://youtu.be/KPuk7sq-RSU

[Chris Taylor Jr]

I think I got it !! it just hit me. its 2d so what I really need is to simply make it 3d ie add THICKNESS

found youtube video I found out how to add thickness and its easy!. right click convert to editable polygon. then modifier list "shell"

done. it now has thickness and so far it appears properly in both maker bot desktop and preview and SEEMS to be printing (it left a hole in the center of the raft. will know for sure in 103 minutes :-) but its looking good and that is EASY to do as well. Nice !!

[Chris Taylor Jr]

Just wanted to five a final update. the SHELL modifier works like a charm. printed 3 complex tubes all perfect! set for .5mm and it does them in a single pass (faster and lighter by a lot!)

Having a new issue (nose cone won't slice crashes makerbot software background program (I assume the slicer) Will start a new thread for that one.

Thank you!

On Monday, March 14, 2016 at 2:53:33 AM UTC-4, Chris Taylor Jr wrote: