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Solid Edit ? Best practice ? Any tips?
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* December 17, 2018, 08:11:51 AM
Folks,

The attached part I want to explode so I can alter some dimension and split in three parts for 3D print.
I have experimented with explode the part twice. But ends up with a lot of lines.
This is a imported step part and not drawn by myself.

Any suggest how I can do ?

Best regards
NeverStop

 
« Last Edit: December 17, 2018, 08:29:19 AM by NeverStop »

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* December 17, 2018, 11:40:16 AM
#1
The part is a single fully joined ACIS solid, therefore exploding from an ACIS produces a TC surface then polyines.  If the part was 3 separate parts grouped or a block, then exploding would separate.  Also if the single ACIS solid was Boolean added with gaps between the parts, then exploding would produce 3 ACIS solids.  But as a fully joined part it cannot be simply exploded.

You can use the 3D slice tool, see help file.  to cut the object into separate pieces.  the method would depend on how you want it slicing.  For Example.  To slice off the top overhang. Slice by 2 points works in front view. Slice by workplane requires a workplane setting up on the underside of the overhang.   Slice by facet works if on rotates the view so one can access the facet on the underside of the overhang.  Slice by plane (3 points) works in ISO view by snapping to 3 vertex points to create a sort of temporary workplane.

 
« Last Edit: December 17, 2018, 11:43:32 AM by Andy H »

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* December 17, 2018, 12:23:06 PM
#2
The part is a single fully joined ACIS solid, therefore exploding from an ACIS produces a TC surface then polyines.  If the part was 3 separate parts grouped or a block, then exploding would separate.  Also if the single ACIS solid was Boolean added with gaps between the parts, then exploding would produce 3 ACIS solids.  But as a fully joined part it cannot be simply exploded.

I suspected this, but I hoped it was some trick.

Quote
You can use the 3D slice tool, see help file.  to cut the object into separate pieces.  the method would depend on how you want it slicing.  For Example.  To slice off the top overhang. Slice by 2 points works in front view. Slice by workplane requires a workplane setting up on the underside of the overhang.   Slice by facet works if on rotates the view so one can access the facet on the underside of the overhang.  Slice by plane (3 points) works in ISO view by snapping to 3 vertex points to create a sort of temporary workplane.

I was thinking about slice tool, but I am afraid it would be difficult to slice the right place.
But I will do my best and play with it.

But after I explode the part completely. Will it be possible to create a solid of the part again ?


Thanks!

Best regards
NeverStop

 

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* December 17, 2018, 01:13:51 PM
#3
But after I explode the part completely. Will it be possible to create a solid of the part again ?

Theoretically, yes.   BUT, in practice, No worth the effort.  It would mean separating the sections (polylines), ansuring no polyline is missed.  Converting all the polylines to ACIS surfaces, then add the required ones together and then hoping it will convert to solid, all without errors creeping in. but the main problem is that curves would end up as flat rectangular or triangular facets, rather than smooth curves.  One can increase the ACIS facet setting before exploding to produce more polylines,  but the more exploded polylines it creates, the higher the risk of failure when trying to convert back to solid.

Definitely not worth the effort.  Attached is how bad the object looks after doing the above at the default ACIS setting, I tried at ACIS quality 90, but it failed to convert to solid - it threw up an error).

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* December 17, 2018, 01:26:05 PM
#4
Quote
Theoretically, yes.   BUT, in practice, No worth the effort.


Ok- I see! Do you know about this is a lack in TC or simply the nature in CAD ?

I undestand the road must be slicing ?

Best regards
NeverStop

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* December 17, 2018, 01:53:02 PM
#5
Do you know about this is a lack in TC or simply the nature in CAD ?
I undestand the road must be slicing ?

I have not much experience with other cad packages, so will have to leave it to others to comment really.  I suspect most lower priced CAD (as opposed to things like Solidworks), will operate in a similar manner.

Slicing is a good way to go, and is the method I use to split before 3D printing.   

Another method I occasionally use if slicing cannot produce what I require, is to.  Draw a sacrificial box, cylinder or extruded polyline just around the part of the object I need to separate, 'Make copy' both the main part and the new object, so there are two of each.  3D boolean intersect one of the main parts with one of the new parts.  then subtract the remaining new part from the remaining main part. Thus leaving two separate parts.      This may sound complicated, but is quite fast once you have done it a couple of times.   

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December 17, 2018, 04:38:56 PM
#6
Ok- I see! Do you know about this is a lack in TC or simply the nature in CAD ?

Simply the nature of CAD.  A collection of Polylines is not a solid object.  A solid object inside a CAD program is, in essence, a computer program (not dissimilar to BASIC) with a list of commands and data (Surfaces, mostly) used to create the 'solid' object.  When you Explode, you throw away the commands that worked with the Surfaces to describe the solid object, so you only have Surfaces.  TurboCAD can, in most cases, convert a Surface to a Solid, but it warns you at the beginning that it may not be exact.  Speaking from experience, the reconstructed Solid object will take up a lot more memory than the original Solid object.

Surfaces are also a program listing that includes commands and Polylines; when you explode them, you throw away the commands and only have the Polylines.  TurboCAD cannot re-construct a Surface or a Solid from the Polylines.  I don't know if any other program even tries, either.


Jeff

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* December 20, 2018, 02:33:21 PM
#7
STEP and IGES objects are "dumb" solids and surfaces.  They give you shape information, but not the means/recipe that they're created by.  They were designed to allow some interchange between programs without using proprietary information, because CAD's a competitive industry.  There's been an age-old chase and catchup between Autodesk's .dwg and what used to be called the OpenDWG consortium, that grew out of IntelliCAD in 1998 using .dwg as its native format, and didn't Autodesk howl about that?  There are some direct editing tools in TC that can be used to rebuild some parts from the external faces of an object.  Facet editor lets you isolate faces using "create surfaces from faces", Quick Pull and recently Tweak Face give some means to thicken/solidify them.  Depending on their relationship and how you thicken them, it can be possible to intersect those solids to recreate a part, and sometimes if the surface is a shape like the half-cylinder shown in this thread that you can see only needs a flat surface to enclose the volume, then selecting it and invoking "create solid from surface" will do exactly that.
« Last Edit: December 20, 2018, 02:55:07 PM by murray dickinson »

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