Here is a screen shot of it- I am trying to subtract the polygon from the sphere but nothing happens. Maybe it is too small to work?

Hi Dragon, can you please upload your .3dm model file? It is hard to tell what might be wrong just by looking at the screenshot...

It doesn't look like the polygon fully divides the sphere into 2 pieces though, it just seems to poke through it at the corners a little. Are you trying to drill small holes in the sphere at those corner points?

- Michael

Yes, I am trying to make holes at the top for a vent. I will upload the file monday since I am heading out the door and will be gone all week without computer access.

here is the file :)

Hi Dragon, the problem in this case is your cutting object has gotten a bit messy, it is made up of a lot of different pieces that are kind of overlapping over top of each other.

This is the problem piece:



If you select it an run Edit/Separate on it, you can then drag the faces that make it up, and you can see that they're kind of bigger pieces that overlap over top of each other:



That kind of overlapped surfaces inside one single object is not good, it will confuse the booleans.

To fix it, go in there and select the 5 bottom edges of the current shape:



And then do Edit/Copy. Now delete the whole object and then do Edit/Paste - this is the basic way to extract an edge from a solid as an independent curve. That should leave you with these curves:



Now run Construct / Extrude to punch those curves up into a new solid. This new solid will have a streamlined simple structure where each side is just one single surface - it will now work as a cutting object for your boolean.



Hopefully that should let some smoke out of your firepit! :)

- Michael