#1 By: John Bryant, August 21st, 2013 08:15
The attached file contains a 1/8" angle stock cut at each end. 4 holes need to be cut next but when I go to Boolean Difference the extruded circle it does a Boolean Union instead. So, I don't get a hole I get two protrusions from my angle stock. All Boolean commands are Boolean Union. Hopefully you all can recreate the issue from the file. Just load and select the biggest object and select Boolean Difference and then select the extruded circle and see what happens for you.part-g47-rv126.96.36.199dm(139.9 KB)
#2 By: Mitch Heynick, August 21st, 2013 08:52
When Boolean operations do the opposite of what you expect, it is almost always that you have one or more parts that you think are closed but are not. These open parts might have their normals facing inwards - with closed objects they always face outwards. As Rhino uses the normal direction to determine how to create the Boolean, and assumes all parts are closed, the operation gets done "backwards"...
In this case it is your angle part that is not closed. Turn on naked edges to see. You can fix those so the object is closed; then the Boolean op will work correctly. If you use Flip on the object you can flip the normals to the outside, then the Boolean operation will work even if the object is not closed.
You might also want to look here and here for more info on Boolean operations and closed objects.
#3 By: Mitch Heynick, August 21st, 2013 09:08
By the way, it looks like you trimmed off the ends of the angle with the curves and then used Patch to cap the open ends - I would not do that, you will not get a good clean surface and it is the probable cause of the part being open. I would just Extrude the curves to make a surface to cut the angle part with then use something like BooleanSplit to split the angle part with the surfaces and throw away the unwanted parts. You could also use Wirecut (direction=Normal) to cut the angle part directly with the curves and keep the object solid.
#4 By: John Bryant, August 21st, 2013 11:16
Ah! Fitting it would be "pilot error" on a fitting for an airplane! Cap wouldn't close the top and bottom which is why I tried patch and then joined them. I was trying the trim with a curve instead of the boolean. I was thinking it would be easier and its not, so like you said, extrude and boolean!
Thank you for you time and energy in answering! I do need to learn the naked edges and analysis tools better...
#5 By: Dave Schultze, August 23rd, 2013 19:19
I did a video on boolean trouble-shooting for my Lynda.com course and it's one of the free ones!
If the link fails, go to Lynda.com, search for Rhino 4, then play the video in Chapter 7 "Troubleshooting solids and Booleans"
FYI : The Rhino 5 course is coming soon.