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When is a solid not a solid
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July 26, 2019, 01:23:00 PM
I'm using TurboCad to make 3D engineering models and to date succesfully printed 30+ models, however I have come across a problem this time that I'm unable to resolve. The attached file shows a Yoke and was produced using "rail extrude", mirror copy and the "pull tool" to extend the cylindrical spoke, semi spherical ends added. The sections (2) were then bolean "added" together to create the object/model as per attached. The properties says it is a "solid".When I save the "solid model" as an .STL file for processing in CURA (creating the gcodes) it show and prints as a "shell".
Any ideas why and what I can do to make it a genuine "solid".At no other time, on any other models has this ever occured

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TurboCAD Pro Platinum 2017 64bit
Lightworks
NVIDIA GeForce GTX770
Intel (R) Core (TM) i7-3820 CPU @ 3.6 Ghz
Windows 10 Pro (64)


July 27, 2019, 08:50:23 AM
#1
Think I have answered my own question. It seems the latest version of Cura has some bugs. In desperation I went back to the previous version and it all works again.

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TurboCAD Pro Platinum 2017 64bit
Lightworks
NVIDIA GeForce GTX770
Intel (R) Core (TM) i7-3820 CPU @ 3.6 Ghz
Windows 10 Pro (64)


* July 29, 2019, 05:28:02 PM
#2
The stl file format only describes the shell of the object.  Even if it was solid in TC, it becomes a collection of triangles describing the surface of the object when it is saved as stl.  The slicer needs to figure out which parts are inside the solid and which parts are outside.

TC Pro Platinum seems to be a lot better than TC Deluxe for making workable stl files.  Ultimately, the stl file is still not a true description of a solid object.

I have been designing 3d printed clocks and there are sometimes parts that end up missing in the slicer.  The biggest improvement is to try to always have a small amount of overlap in objects that will be 3d added or subtracted.  The next step may be to switch to a better file format.  Obj or 3mf seem promising.

Steve

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July 29, 2019, 11:08:39 PM
#3
Thank you Steve (323) for your reply. What you say certainly confirms the evidence. The part was formed from a 2d circle which was rail swept along a poly line. Essentially a zero thickness object extruded along a complex path and I just think Cura had a problem interpreting the part. Anyhow, by resetting (reinstalling) the program all seems to be okay again. I did wonder about using obj or 3mf, something to try today.
Many thank for your detailed reply
Cheers
Steve Edwards

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TurboCAD Pro Platinum 2017 64bit
Lightworks
NVIDIA GeForce GTX770
Intel (R) Core (TM) i7-3820 CPU @ 3.6 Ghz
Windows 10 Pro (64)


July 30, 2019, 01:02:10 AM
#4
TurboCAD 2019 has the option, when saving as STL, to perform an integrity check.  You can also specify that it automatically closes holes.


Jeff
 

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TC Pro Platinum 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1


* July 30, 2019, 04:51:45 AM
#5
Slicers don't decide what's inside or outside of .stl triangles.  An integral part of .stl format is every triangle facet having a defined normal that specifies that.  The format is strict about defining a watertight, manifold object, ie a "solid", so if your .stl isn't, that's not because of the file format, it's because your .stl doesn't comply with that geometric parameter.  That is, it isn't an actual .stl, it's just formatted correctly and has been given that attachment.  Stl was specifically designed to not be modelled with, it was intended to give a faceted approximate (with definable resolution/surface approximation accuracy) output of a single part that could be used for rapid prototyping, intentionally resistant to precise reverse engineering back to the original CAD model and to being edited or amended.   Complaining that .stl isn't cooperative or "workable" for modelling or ostensibly simple editing is a lot like blaming .pdf drawing output for not being able to be directly edited in CAD apps.  That's what the developers of the file formats intended. 

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