CAD file scaled for use in drawing 3D model

jack_erhart

I recieve CAD files out of AutoCAD from my CAD person.
The files show a group of different views of locomotives I model.


I would like to be able to scale the CAD files so that the entire group sizes correctly.
Then take each indivitual component and place it into it's own file to model separately.

Can someone explain how the above workflow could happen  at Onshape?

Thanks

MichaelPascoe

Welcome to Onshape!

Here is one way to do this:

• Import the dxf or dwg files into your onshape "document".
• Create a part studio.
• Inside the part studio, create a sketch.
• While inside your sketch, insert the imported image. (I recommend using this as a reference only. Create a separate sketch for your modeling. One that is properly constrained. See the Onshape learning center for the best way to learn Onshape)
• Once your image has been inserted, while inside your sketch, place one dimension with the dimension tool, the entire sketch will scale accordingly.
• You can then create part studios and new sketches and either copy/paste the portions of the main sketch that you need or derive the entire main sketch into the other part studio.

Note that Onshape has trouble using large file size dxf or dwg files.

Importing and scaling a dxf

jack_erhart

Could you slow your example down to about half speed. Makes my head swim just trying to follow! LOL! Great stuff. Thank you.

jack_erhart

You were right. I tried importing my original cad file into a sketch, and it said I had to many entities for that one file.
In that case, I tried copying and pasting unto a sketch in my Part Studio, but it seemed a bit hung up there also.
Any suggestions to a better workaround?

MichaelPascoe

After I recorded it, I noticed it was a bit hard to follow. I will keep that in mind for future tutorials.

Something that may work is to "crop" the dxf to one train view at a time so that there are less lines. You will need to find some other dxf editing software to do that. 

Another alternative is to capture a high quality screen shot of it. Then insert the picture into onshape and trace that. This is the approach I would take. I use it for tracing trim profiles.

jack_erhart

Thanks Michael,

But I'm using CAD files so that I can snap to points for 3D modeling. So the tracing idea really won't work for me.

It's interesting, when I copy all the lines and points for one area of the orignal CAD drawing, and then copy it, I find I can only paste it into a drawing. But then the drawing becomes a picture of the copyed area, with points and lines, but can't be navigated in. Like zoom or pan or any other navigational way. If I click on the drawing tab, and then export out to a DXF file, import it back into Onshape, I can then insert it into a sketch. Seems like a wonky way to do things.

The original file was done in MM, and my system on Onshape is set for Inches. The also seems to cause issues with sizing.

jack_erhart

Got the frame into a Part Studio, it's the proper scale. but it looks like this.
The plane profiles seem very small for some reason.

MichaelPascoe

Got it. That makes sense.

That does sound strange. It should not be doing that.

The planes can be resized if you click them then drag the corner manipulator points.

S1mon

Keep in mind that DXF (like STL) is unitless. The amount of money and time that’s been wasted on that decision by the world is likely in the billions.

jack_erhart

Got the frame into a Part Studio, it's the proper scale. but it looks like this.
The 

jack_erhart

One other thing that seemed strange. My preference measurements are set to inches, but when I'm drawing a line or rectangle, the measurment read out is MM. Is there another setting I not aware of in Part Studio or Sketch?

jack_erhart

S1mon said:

Keep in mind that DXF (like STL) is unitless. The amount of money and time that’s been wasted on that decision by the world is likely in the billions.

Could you clairify your statement please? Would you suggest another format?

S1mon

I use DXF and STL all the time because they are a lowest common denominator format for certain types of data. That said, neither format specifies the units which seems insane. It needs to be communicated along with the file. Depending on the CAD system, when someone generates a DXF or STL it's either in the units of the CAD file or it's set by some export options. Similarly when those files are imported, either the CAD system or the user makes an assumption about what units the files are in and sets that. Because the units are not baked into the files themselves, this leads to many errors where things are off by a factor of 25.4 or some other permutation. One project I worked on ended up with some antenna PCBs getting fabricated which were 25.4 times larger than intended. Their only function was to remind us to double check units and dimensions along the way.

For 2D information you could also potentially use IGES since it does capture the units. STEP typically doesn't include 2D information.

A common workaround with DXF files is to include a 10mm square with a dimension on it (ideally in text which is done with lines, not a font which disappears) to indicate the expected scale/units.