Hi Hongjie...

I've looked at your part. You're going to have difficulty getting this object shelled as it's currently modeled. It is certainly possible but the technique will be far too complex for such a simple part.

Shells can be tricky. They have some limitations that can't really be avoided... so you have to carefully plan to work within those limitations to be successful. The small left bottom corner was a good example of one of the limitations of a shell feature.

In your image, that bottom corner has a round along the outside edge of 1.50mm yet you're trying to shell the part to 2.00mm. The easiest way to resolve this issue is to set that outside round to at LEAST 2.00mm. Leaving it at 1.50mm guarantees a failure in that corner. Your options are:

• Increase the round to 2.00 which will generate a sharp corner if you shell to 2.00mm.
• Increase the round to greater than 2.00 (for example 2.50mm) which will generate a round if you shell to 2.00mm
• Leave the round as-is at 1.50mm and decrease the shell thickness to 1.50mm

This is the easier of your two problems but it illustrates what you're up against. Rounds along the outer edge will be reduced by the thickness of your shell. If your outer round dimension is 6mm and you shell to 1.5mm thick, the inner round will be 4.5mm.

Now then, if you apply that logic to the blended surface, you'll immediately see the problem. The blend creates some very odd geometry in the corners where the blend meets the flat extrusion. There are numerous little tricks you can use to preserve this geometry and make it all a constant thickness. But the real solution here is to remake the original geometry. Unless this part already exists (in which case you must make it as-is), you should consider changing the way it's modeling so that it can work within the limitations of a shell.

Many times, designers will incorporate outer rounds or other devices along problematic edges so the shell command has a greater chance of success. Sometimes adding rounds along tricky edges makes all the difference in whether or not the tool will work correctly or fail.

I was able to get a little creative with your model and almost get it to work with just some clever reworking. Your biggest problem is the blend. Here are some solutions:

• Make the blend as a thin feature with a wall thickness of 2.00mm thus eliminating the need for a shell at all. Add a 2mm thick extrusion at the bottom to cap it off.
• Remodel the part so the blend is created BEFORE the extrusion. Leave the blend as-is and then apply the 2mm shell to JUST the blend. This will succeed. Next, go back and make the top extrusion.
• Leave the model as is... but change the first extrusion to be a SURFACE with capped ends instead of a solid. After the blend, add the 2mm shell. You'll be left with a perfectly shelled bottom piece but the top piece (extrusion) will still be a surface (non-solid). Once you have the shell in place, select the top extrusion and select Edit>Thicken and give the surface a thickness of 2mm.

I actually used that last technique and it almost worked. I ended up with a 2mm wall between the top extrusion and the bottom blend. I tried a few methods of blowing a hole in that wall but due to the way the geometry falls, you're left with a slight "lip" that's obviously not desirable.

I'm uploading the model just so you can take a look at it. Once I complete a tutorial for another message thread I'll go back and re-model your object in a way that it can be shelled more easily.

Take care...

-Brian