Modifying a Complicated Imported Step File

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
Post Reply
hjl5181!
Posts: 12
Joined: Thu May 14, 2020 1:06 pm

Modifying a Complicated Imported Step File

Post by hjl5181! »

Hello,

I was wondering if i could get some help with modifying an imported Step file of a particular object that I have?

To summarize what I am doing/what has been done, I received a Step file from a vendor. It came together as a Part with several Bodies. The Bodies are located at particular locations (ie, XYZ points and rotations). In the real world, the individual Bodies are all linked together and move with each other (think almost like a machine of some type: one part causes the next part to do something). I tried just moving one Body just to see if the rest of the Bodies would update their location accordingly, but they will not because it is not in a A2Plus assembly. Therefore, I am trying to take the individual Bodies and create my own A2Plus assembly, that way I can move one component and the other components will update their location based on what was just moved.

I have copied all of the individual Bodies and saved them in their own separate FreeCAD file. This is so I can simply add them to a new A2Plus assembly, set my constraints between the individual components, and have an assembly that I can move around. I have started my assembly, but I am running into issues. It appears that FreeCAD is interpreting some of the features as being b-splines. Based on what I have found, I cannot have an axisCoincident constraint with b-splines.

To try to overcome this issue, I was going to try to modify the individual Body that I copied into its own separate FreeCAD file (file attached). I also attached a separate document with a red start on it to signify the area that I would like to modify. If you try to click on this area and try to create a sketch on the PartDesign tab, a message pops up with a description stating that there needs to be an active body.

I have tried a couple different things to try to correct this situation, such as creating a clone and creating a base feature. Note: When I create a base feature, a message pops up and states that the selected shape consists of multiple solids and that this may lead to unexpected results. When attempting to do either option, it ultimately does not work. I am able to select this face and draw whatever I want on it (ie, a circle). However, when I try to extrude/cut the drawing, this operation does not work.

If someone could give me some ideas/direct me in the right direction as to how to draw on this particular surface, that would be greatly appreciated.
Attachments
FreeCAD Help.FCStd
(586.4 KiB) Downloaded 19 times
FreeCad Help.pdf
(199.6 KiB) Downloaded 38 times
hjl5181!
Posts: 12
Joined: Thu May 14, 2020 1:06 pm

Re: Modifying a Complicated Imported Step File

Post by hjl5181! »

Also, here is the information for what version of FreeCAD I am using.

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.4 (GitTag)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 980bf9060e28555fecd9e3462f68ca74007b70f8
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)
TheMarkster
Posts: 2642
Joined: Thu Apr 05, 2018 1:53 am

Re: Modifying a Complicated Imported Step File

Post by TheMarkster »

I think the biggest issue is the object has defects, perhaps intentionally placed there by the manufacturer. Because of the defects boolean operations, like cutting, are likely to fail. To see them, select the object, then in Part workbench use the CheckGeometry tool. In the CheckGeometry settings tab enable BopCheck for a more thorough test.

But despite the defects I was able to successful attach a sketch to the face, create a rectangle, extrude it into the object, and boolean cut it out of the object.
Snip macro screenshot-42d13d.png
Snip macro screenshot-42d13d.png (46.84 KiB) Viewed 439 times
Steps to reproduce:

Go to Sketcher workbench.
Select the face.
Create a new sketch, select default attaching mode that is offered.
Add your geometry to the sketch.
Go to Part workbench.
Extrude the sketch.
Toggle the reversed property of the extrude object if it extrudes in the wrong direction.
Select the object first, and then select the Extrude, and then do the Part menu -> boolean -> cut.
My FreeCAD video series on youtube: https://www.youtube.com/c/mwganson
hjl5181!
Posts: 12
Joined: Thu May 14, 2020 1:06 pm

Re: Modifying a Complicated Imported Step File

Post by hjl5181! »

Thank you very much for your help! I will definitely keep this in mind when I am working with other imported Step files with issues like you have found. I suspected that our vendor intentionally created a model that had some issues with it, that way no one else could easily reproduce their model. I greatly appreciate your help!
hjl5181!
Posts: 12
Joined: Thu May 14, 2020 1:06 pm

Re: Modifying a Complicated Imported Step File

Post by hjl5181! »

Just as a quick update, for some reason I could not get the steps that you provided to me to work. I was able to create the sketch on that surface and extrude the sketch into the body. However, when I would the select the object first and then select the Extrude, then try to do a Boolean cut, I am unsuccessful. The following message pops up: "The use of non-solids for boolean operations may lead to unexpected results".

Regardless, I was able to come up with a workaround for my application. I simply did not do the Boolean cut and left the extruded feature on the part. I was then able to use the geometry of the extruded feature to create the constraints that I needed for my A2Plus assembly.

Once again, thank you for the guidance.
TheMarkster
Posts: 2642
Joined: Thu Apr 05, 2018 1:53 am

Re: Modifying a Complicated Imported Step File

Post by TheMarkster »

I got the same warning, but elected to proceed anyway and the cut worked. If you select the step import and in part workbench -> compounds -> explode compound you will get a group of new objects with quite many in the list, hundreds if I recall correctly. Only the first 2 are solids. The rest are non-solids and I think the reason for the warning.
My FreeCAD video series on youtube: https://www.youtube.com/c/mwganson
User avatar
M4x
Posts: 792
Joined: Sat Mar 11, 2017 9:23 am
Location: Germany

Re: Modifying a Complicated Imported Step File

Post by M4x »

For this specific part it is a practical approach to remodel it in FreeCAD don't you think?
Post Reply