Hi Brian,

> Is it possible to have a Boolean union option to preserve the 4 edges?

Unfortunately I'm not sure how I would do that - there are not currently any options to set for boolean union, and so the way it works is you select things you want to union, then run the command and it immediately does its work and finishes.

To set options I'd need to introduce some extra stage in the command where it would wait for you to set the options, and that would have a significant negative impact of causing an extra step for every single boolean union even if you had no interest in setting that particular option...

I have some general idea that in the future there may need to be some options to go along with "depth limited" booleans which for boolean union would be for making protrusions of 2D profile curves coming out from a solid.

Or I guess maybe there could be a separate command for setting boolean options which would then let you set plane combining on or off for all boolean commands maybe?

At any rate it's not quite so simple as just adding in an option because there is at the moment not any stage in the command for options.

Another way you can get this done currently is to delete the internal side walls where the solids are touching each other and then use Edit > Join to glue the pieces together.

- Michael