Hi angleiclight - use Join if you have surfaces that are touching edge to edge, like this:



Above I modeled 2 surfaces in separate steps by extruding those 2 different curves.

That has created 2 surfaces that are independent objects, but they are adjacent to one another and have an overlapping edge.

You can use Join to glue together 2 surfaces that are separate but adjacent like this into one single connected object. Sometimes this can be used to do detailed tweaking to a couple of surfaces of a solid - you can use Edit/Separate to break out some surfaces from a solid, edit them by trimming them/transforming/etc.. then join the edited surfaces back with the others to make a solid again.

Join is also used to glue together 2 adjacent but touching curve segments into a longer curve object.


The booleans are meant to be used when objects actually push through each other so that they need to be intersected with each other to get the result.

Like for example here are 2 solids:



If you arrange these so that they are punching through each other like this:



Then you would use boolean union to fuse them together into a single object and discard the interior parts:



That does not involve just gluing existing edges together, that involves calculating the intersections between the 2 objects and creating new edges where the solids/surfaces intersected, for example a new edge is shown highlighted above.


So Join is for gluing edges for surfaces that are already touching edge-to-edge, and booleans are for fusing objects together that need cutting and intersecting to happen.


Also another way to say it is that Join does not discard material, while booleans are focused on discarding some part of the objects involved, like above they discarded the parts of the sphere that were inside the cylinder, and discarded the parts of the cylinder that were inside the sphere.


- Michael

Michael, thanks much!

So, would you use join if you were modeling, say, a spaceship and you have the body, but want to put a lot of smallish details on the surface that look like small cubes, etc, glued on?

Do you only use boolean when you want one object out of two or more? How do you relate this to my above example, where you want lots of objects appearing to be "sitting on" or attached to the object underneath it, but not necessarily anything mathematically happening?

(Am I making sense with any of this stuff?)

Sorry if you had to repeat anything found elsewhere... :(

- A

Hi angeliclight,

> So, would you use join if you were modeling, say, a spaceship and
> you have the body, but want to put a lot of smallish details on the
> surface that look like small cubes, etc, glued on?

Well, it depends on how you specifically modeled those details.

If you created the small cubes as solids (like say by the Box command), then you would use booleans to merge them with the main hull.

It's only when you have individual surfaces that touch each other that you use Join.


So for example for a small cube shape - if you happened to build the cube shape by drawing 6 individual planes that touch each other, that's when you would use Join to glue them together into a single solid box.


It's somewhat more common to use booleans though, modeling things by doing one surface at a time (where you would then use Join) tends to be a more advanced type of workflow. It is easiest to start out by creating pieces as solids and use booleans to fuse them together.



> where you want lots of objects appearing to be "sitting on" or
> attached to the object underneath it, but not necessarily anything
> mathematically happening?

If your final result is going to be a rendering, and you don't need to do stuff like put a smooth fillet between the pieces, then you can often times just move pieces like that into position and leave them as separate objects and not actually do the work to make them in to one single object at all.


- Michael

I guess the key thing to stress here is "individual surfaces".

If you have created 2 or more surfaces that are totally independent objects but have been arranged to be sitting right next to one another, that's when you use Join to glue them together.

For everything else, you use booleans.

- Michael