Units When Importing an AutoCAD Model

[Chris_Molland]

Hello

We are using Inventor 2013 (Windows 7) and am trying to import an assembly created by a third party using AutoCAD. For the sake of this question let's assume the AutoCAD file contains a cube which is 10 x 10 x 10 units. The part should be 10 x 10 x 10 mm in size. We don't use AutoCAD so are unfamiliar with it but it appears to have no specified units, I could be very wrong here!

In Inventor we import the .dwg file and the cube is 10 x 10 x 10 inches in size.

We can't figure out if the person who constructed the cube built it too large (reading mm off the drawing but constructing it using inches) or if we have missed something when importing the file into Inventor. We could scale the AutoCAD assemby but this could lead to a small but significant margin for error so we want to understand what is happening first.

Any advice would be very gratefully received.

Thank you.

Chris

[Cadmanto]

Chris,

What is the units setting in your template that is used for this Inventor file?

Do you know what the units setting is for the Autocad file before it is exported?  You say 10 x 10 x 10 units for Autocad.  Don't know which units (inches versus mm).

In Inventor if you go to Tools>Document Settings>Units this will tell you what the current setting is.

If this solved your issue please mark this posting "Accept as Solution".

Or if you like something that was said and it was helpful, Kudos are appreciated. Thanks!!!! 

     

[Ray_Feiler]

Ask them to type Measurement at the command line in AutoCAD. If they get unknown command they are using a older version of AutoCAD that is unitless.

Command: MEASUREMENT
Enter new value for MEASUREMENT <1>:

0 = inch, 1 = Millimeter

[JDMather]

Do you have access to AutoCAD?

Open the file in AutoCAD and run the -dwgunits command (with the minus sign).

That will return the units of the AutoCAD file and gives you the option of translating the units.

[Chris_Molland]

Hello Scott,

Thank you for your reply. We're looking into it. Please see further down this thread for more information.

Regards

Chris

[Chris_Molland]

Hello Ray

A very helpful suggestion thanks. It would appear that the originator of the 3D model in AutoCAD created a document which had inches as its unit but then entered millimetre values to all of the dimension values!

Regards

Chris

[Cadmanto]

Chris,

It would appear that the Autocad file needs to have the unts fixed before importing it into Inventor.

Tha alone might fix your issue.

If this solved your issue please mark this posting "Accept as Solution".

Or if you like something that was said and it was helpful, Kudos are appreciated. Thanks!!!! 

     

[Chris_Molland]

Hello JD (I hope that's OK)

This is exactly what we were looking for, and had just discovered ourselves, thank you.

Before we give it a go we are going to create a 10 x 10 x 10 inch cube, import it into Inventor and establish that it remains the correct size and then use the -dwgunits command to change it's units to mm and import the cube again into Inventor to prove the method.

All going well we will then apply the method to our client's 3D AutoCAD file. I'll keep you posted.

Regards

Chris

[JDMather]

I would of course do a test first (and keep a backup file) so that you understand the behavior.

[dan_inv09]

Is this what we're talking about?

[Chris_Molland]

Hello

Thank you to those who have contributed so far.

We've been wrestling with this all day and have not yet cracked it! This is what we have tried:

1. Created a new AutoCAD file.
2. Using -MEASUREMENT set the units to Inches (0).
3. Constructed a 20 x 20 x 20 inch cube.
4. Saved the file.
5. Import the file into Inventor. Note the units are detected as inches.
6. In Inventor measure between 2 faces and this remains 20 inches across. So far so good.
7. Open the original AutoCAD file and run -DWGUNITS. Set the units to mm (1), set 'yes' to both import options, set 'yes' to scale the model.
8. Run -MEASUREMENT and confirm units changed to mm (1).
9. Save the AutoCAD file.
10. Import the revised file into Inventor. Note the revised model's units are detected as mm (1).
11. Measure between 2 faces in Inventor and it is 508mm, not 20mm which we hoped to see.

We then thought that perhaps we had misunderstood the 'Scale model..' part of the -DWGUNITS command so we tried again and this time entered 'no' to scaling the model. We got exactly the same result!

Now perhaps we've missed something as we're not familier with AutoCAD but it does seem odd to me.

Dan pointed to the Units section of the import dialog nox and indeed this was our first thought. However we found that if you import a 20 x 20 x 20 inch cube and set this to mm the cube remains the same physical size but the Inventor part is created with mm as its unit of measure so when you measure the cube it is 508mm across the faces.

We believe the original modeller built the assembly using Inches as the AutoCAD unit (confirmed by issuing -MEASUREMENT on the client's file, but entered the mm values. We want to change the unit to mm and have AutoCAD scale the model so that what was 20 inches is now 20mm.

I look forward to your thoughts.

Regards

Chris

[Ray_Feiler · Accepted solution]

If you just change the Measurement value to 1 in the AutoCAD file and save it should do what you want.

[Chris_Molland]

Hello Ray

You are spot on. I don't know how we didn't see that.

Thank you very much.

Regards

Chris