I identified the Part Tree information for a previous boolean subtract I had performed.

This put the material back which was removed by the boolean subtract operation.

I then performed a boolean subtract again and this time it succeeded.

I believe now the original failure of the boolean subtract operation was because I had performed a boolean subtract operation twice using the same object. The object being subtracted was identical, and placed in the exact same location as a previous operation. It seems TurboCAD cannot perform the same Boolean Subtract operation twice, even it the 2nd operation takes away more material. It somehow fails to identify the fact that the shape of the model has changed from the 1st operation to the 2nd. This seems like a bug, if you ask me.

If TurboCAD works this way, this is wonderful news. This means individual Boolean Operations can be backed out without needing to 'Undo' all operations performed after that operation.

I have an extremely complicated model, which is built from many library components, which are fairly complicated models themselves. My process was to build a new version of the model from scratch each time. It seems like this is not necessary, if you can identify the component in the Part Tree associated with a particular step in the build process.

Is this true?

John