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Working with imported STEP files.

jcdammeyer

Senior Member
I'm running into this fairly often lately. I use either Fusion360 or FreeCAD 0.19 to create a step file from the stl file or if I have it available I just load the step file from the original designer. As the screen shot shows there's one component that is called the imported step file. Onto this I put a hole all the way through with a sketch and cut extrusion. If I want to extend the smaller hub by 5mm I draw a circle on it, extrude it up 5mm, then also on the back side draw the 4 small holes and extrude them up through all. Very tedious and this is a simple part. Is there an easier way?

Now if I want to bring in a step file often it has loads of little facets and it's huge. In this case it was easier to take some measurements and recreate it making the whole stl to step to ad_prt a bit of a joke. How does one remove all the facets. My friend with Fusion was able to do this quite easily.
 

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  • StepHub.AD_PRT
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HaroldL

Alibre Super User
It looks like somewhere along in the conversion process all the arcs and circular edges are converted into line segments. You're probably going to save yourself some headaches if you just take some measurements and recreate the part(s) in Alibre.
 

JST

Alibre Super User
I do not understand that at all. Most STEP files are not like that.

The STL files are faceted etc, and presumably when exported as STEP those "features" are preserved.

If that is the only way to get a STEP file out of Fusion or Freecad, it sounds like what I call a "punishment export"............. making the exported file nearly unusable just because "you obviously want to use some other program", and the program authors do not like that. Autocad had some "punishment exports", and other programs have had them as well, slamming everything onto one layer, breaking up "blocks", or turning curves into segments. That sort of nonsense.
 

jcdammeyer

Senior Member
I suspect FreeCAD isn't into punishing anyone. Way back during the Geomagic time we could import stl files and then save them as part files. That sadly vanished when it became Alibre again. The other sad thing of course is that so many people publish stl files but don't include cad portable (somewhat) stp files. But that's a different topic.

Anyway, my real question remains the same. The step files appear to be one of the transfer methods of choice (IGES too) and what you get into the CAD software is one element with hundreds of edges, faces and verticies. Aside from the fact that the Fusion360 guy was able to create a nice step file from the stl while I couldn't. Mine as exported by either Fusion or FreeCad (I have both) came out over 20MB in size with lots of facets. My friend was able to make a small one 7MB in size. I've only supplied screen shots but the that's the question. If I import a 20MB step file like the Large one are there tools within AlibreCAM (that must exist in Fusion36o I guess) to be able to 'tweak' the design to create the Small version. At least on that I can overlay drawings and cut/extrude or even just utlimately copy.
 

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  • FlexSplineSmall.jpg
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bigseb

Alibre Super User
Feature recognition. Apparently Fusion has this, wouldn't know, never used it. But will convert the multifacetted (and huge) stl files into smooth (and much smaller) vector geometry.
 

JST

Alibre Super User
Of course, the basic issue is STL file conversion. And the NEED to do it that way in the first place.

While Alibre "could DO it", I was never able to get a decent part input to Alibre when starting with an STL file. I regard STL files as being "on the other side of a trap door", it seems to be effectively a one-way process. STL files are so different that the conversion appears to be only approximate. Sort of like doing a CAD model from a photo by tracing it. You may get, with feature recognition, a pretty good rendition, but it will not have definite dimensions as the STEP file does.

If the only way to get a file out of Fusion or FreeCad is as an STL, then that is a restriction that is fairly unacceptable if you want real and accurate models transferred. Yes, it is a "punishment export", a deliberate limit to what you can do with a file outside of the program.

A STEP file is a very clear and accurate file format that loses nothing in the transfer other than the part history. The actual geometry is not lost. Any credible CAD program ought to produce a STEP file.

And, Fusion DOES, as I understand it. Just maybe NOT if you use the free version, which is apparently deliberately hobbled and limited (no surprise, they are not giving away the store). I have no idea about FreeCad.
 

jcdammeyer

Senior Member
OK. Just wondered if I was missing the usage of a magic feature. Doesn't hurt to ask. I'm guessing the real reason for being able to import step files is to add them to assemblies and there's nothing in the cards that says here's a step file of a part.

Make the holes 20mm deep instead of 25mm. Heck, even the circles on most imported step files aren't circles but a series of arcs. We know it's round. So how to fill in a hole to make it not as deep?
 

JST

Alibre Super User
................................. Heck, even the circles on most imported step files aren't circles but a series of arcs. We know it's round. So how to fill in a hole to make it not as deep?
That seems to be a feature of the program and not the STEP format. Some programs, such as Solidworks, seem to make all cylindrical shapes with two half cylinders, for example.
 

bigseb

Alibre Super User
Make the holes 20mm deep instead of 25mm. Heck, even the circles on most imported step files aren't circles but a series of arcs. We know it's round. So how to fill in a hole to make it not as deep?
Direct editing. Or create a feature to 'plug' the hole.
 

jcdammeyer

Senior Member
That seems to be a feature of the program and not the STEP format. Some programs, such as Solidworks, seem to make all cylindrical shapes with two half cylinders, for example.
That's just plain dumb. I still think the reason I like Alibre so much is it feels like the right way to do things. At least for me. Could never design with Autocad. Turbocad was another try but failure. Don't like Fusion nor FreeCAD. And then came Alibre. Wow! Although assemblies are much harder to work with now then when it first came out. Seems clumsier.

However this example shows that the half cylinders are a function of step files. Create the part in Alibre and export as step and then import step file and save as part. What was a circle is now two half circles and no way to mend it back to being round. Which then has a dimension that could be changed. Even if just a 'knit' operation creates a sketch that overides the step part. Then we have a sketch with a circle that can be reduced in diameter.

To an amateur like me this sort of human factors ease of operation should be a no brainer.
 

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  • SquareBlock_step.AD_PRT
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  • SquareBlock.AD_PRT
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jcdammeyer

Senior Member
??? You mean stl, right?
Nope. STL can't be imported by Alibre anymore. So I've been talking about how using other CAD programs to bring in an stl and create a step that can then be edited by Alibre. But the reality is Alibre is almost helpless with step files other than as additional parts to add to an assembly. So much for universal CAD format. But then I doubt any of the other CAD programs can take a step file they created and then edit it as if it was in native format.

But maybe that's where the work should be done?
 

jcdammeyer

Senior Member
So here's the plug and hole solution. Is that the right way or are there others?
 

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  • SquareBlock_step_mod.AD_PRT
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Nick952

Senior Member
Have a look at this video:-

This is your hub face moved 5mm, the Square Block hole depth reduced by 5mm and the Square Block hole Dia changed, using the Direct Editing Tools :-
 

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  • SquareBlock Hole Depth Reduced_step.AD_PRT
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  • SquareBlock Hole Dia Change_step.AD_PRT
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bigseb

Alibre Super User
A real pity that DE features were removed. That push/pull pocket/boss is no more. There are one or two others missing too. DEs are awesome, I use them a lot. Wouldn't mind seeing more work put into them.
 
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