Odd Subtraction


#1

Problem Subtract.3dm (14.9 MB)

In the attached file, I have a hull shape (and two gun tubs):

If I subtract the gun tubs from the hull, this happens at the bow:

How can I prevent/correct/fix?


(Pascal Golay) #2

Hi Jim - the vertical -ish surface from the deck to the rail is not meshing cleanly - run DivideAlongCreases SplitAttangents=Yes on the ship and it should clean up. Man, you make some weighty surfaces! - I’d run FitSrf anyway on this skinny vertical surface to lighten it up a little.

-Pascal


#3

Thanks much.

You should see the whole monster. Still not finished yet.


#4

I don’t now what changed but DivideAlongCreases SplitAttangents=Yes is no longer working for this problem. I start with this:


Then I subtract a solid at the stern and I get this:

Here is an example. Two oddities:

  1. Subtracting the stern gun tub on the right (starboard) side does not cause a problem but the one on the left (port) does.

  2. I have included a surface going lengthwise through the hull. I cannot split the hull using that surface. I tried wirecut but it fails silently.

split.3dm (11.2 MB)

Any other suggestion on how to get rid of this?


#5

This is a simplified version of the one above (still rather complex). Subtracting (or splitting) the aft tubs from the hull causes chaos at the bow.
Subract 3.3dm (3.6 MB)


#7

I note that even doing a WIRECUT across the hull causes the problem.


#8

You probably have some bad joins in there and when you do something like a Boolean operation, it remeshes the part - so you’re getting a bad display mesh in that area. I might try extracting the surfaces around the problem area and rebuilding the edges, then rejoining one by one. It might show you the problem.

–Mitch


#9

Rebuilding didn’t do anything.

The only thing I found that makes the problem go away is to explode then slice everything at the bow. In other words, split the deck and sheer strake into two pieces. then I created the bow. Then I created everything else. Joined them together then subtracted.


#10

That was RebuildEdges not Rebuild, just to be clear, the two are not the same thing. The fact that slicing the bow off and creating new surfaces solved the problem convinces me even more that it was an out of tolerance edge/join problem or some bad surfaces. Impossible to know for sure without seeing the surfaces in question before “surgery”…

–Mitch


#11

It was rebuildedges that I did before. The post above has the edges before cutting off the bow.

The same thing happened to the USS Wisconsin. After a collision with a destroyer the bow was cut off. The bow was removed from the USS Kentucky and grafted on to the Wisconsin.


#12

:joy: