Attaching imported CAD objects breaks normals

[kosso_olli]

There is a second solution though: After opening the file, convert both parts to edit mesh by right clicking---> convert to edit mesh. Then collapse both parts using the single object mode in conjunction with the collapse utility. One of the objects will have it's normals rotated, not flipped. You can check by appliying and edit normals modifier on top (adjust display length as needed). Select all the normals of the object with rotated normals, and then rotate them. Depending on which object has the normals messed up (seems to be random), the value is either 90° or -90° on the Z-axis. All normals will be pointing into the same direction now.

[Alex_M]

Indeed, attaching the body objects and then converting works as expected.
Personally, I decided not to use the body objects, because they are ancient. The implementation is not up to date. I prefer the tesselated method on IGES/STEP import. This might not be necessary with these two parts. However, if you have to deal with 1000 parts imported as body objects, Max will simply stall.

If by "tesselated" you mean turning on "convert to mesh" at the import dialog, I tried that and it still causes the normals problem.

There is a second solution though: After opening the file, convert both parts to edit mesh by right clicking---> convert to edit mesh. Then collapse both parts using the single object mode in conjunction with the collapse utility. One of the objects will have it's normals rotated, not flipped. You can check by appliying and edit normals modifier on top (adjust display length as needed). Select all the normals of the object with rotated normals, and then rotate them. Depending on which object has the normals messed up (seems to be random), the value is either 90° or -90° on the Z-axis. All normals will be pointing into the same direction now.

This actually worked! Thank you SO much! You seem to know your normals.

[kosso_olli]

If by "tesselated" you mean turning on "convert to mesh" at the import dialog, I tried that and it still causes the normals problem.



This actually worked! Thank you SO much! You seem to know your normals.

Yes, indeed. There hardly is a problem regarding normals that can not be fixed in Max. That's actually what I like about Max in favor of other packages: It can deal with any kind of file format and it has a lot of tools to fix every problem. You just have to know where the various tools are hiding.
Edit normals modifier comes in handy if you get visible seams between surface patches by the way. In this case you will find two or more vertex normals per vertex along the seam, each showing in slightly different directions. Simply copy the value of one if these normals, and paste it to the "outliers". Depending on the tesselation and the size of the seam this might be a tedious process, but sometimes it is the only option...

[Paul Oblomov]

Btw, can you share original cad ?

[Alex_M]

You can download it from the CAD.zip archive attached in this post.