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Why are Shut-off Surfaces different between these analogous features?

Question asked by Steven Snyder on Apr 15, 2015
Latest reply on Apr 17, 2015 by Doug Seibel

In the part shown below, I have a number of latches which have a drafted relief underneath so this part can be made using a two-piece mold instead of having a sliding core. The latches are identical in every way except the width.

I need to create shutoff surfaces so I can make my tooling split.

 

Using the Shut-off Surfaces tool, selecting the edge loop on the latch at the bottom left of the image (below) and selecting Tangent for the patch type works perfectly, creating the surface I need. However, on the middle latch, the surface is incorrect. I can change the direction of the red arrow to make what looks like it should be the surface I need, but upon closer inspection it is offset by some amount and doesn't line up with the bottom hole. That's what is happening at the top right.

 

The draft angle of the latches is actually different from the undercut relief, so my guess was that this tool is simply following the angle of the latch surfaces downward. It doesn't explain why the bottom left latch works and the others don't... but I changed the draft angle so it's the same for everything and I can still get the bottom left latch to work and the other two produce the middle result shown in the picture.

 

What's going on here? How do I just get the shut-off surfaces to all look like the one on the bottom left?

shutoff surfaces.PNG

The Solidworks manual says I should be able to do this. In fact the example feature is the same feature I have...

 

See: 2014 SOLIDWORKS Help - Shut-off Surface Fill Types

sw-shutoff-surface-fill-types.PNG

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