Hi Will - yeah the way that it works is that Trim is more of a surface operation where it will cut the "skin" of a solid and the result will be surface fragments and not a solid anymore until you use Join later on to join those fragments back into a solid.

Booleans try to operate on solids as a volume and will try to give you solids as the result.


But either of them can work with curves as the cutting objects.


When using a curve as a cutting object in Trim, it is the same effect as if you projected that curve on to the surfaces.

When using a curve as a cutting object in Booleans it is similar, except instead of just projecting the curve on to the surface it is the same as the curve being extruded into a solid (if the curve is closed, or a surface if the curve is open) and then that solid being used as the cutting object.

So for instance if you use a boolean with a circle as the cutting object, the hole that is produced will include "side walls" which are the result of the circle being extruded into a solid cylinder.


As a kind of demo, take a sphere, and then draw a line that crosses the sphere so that it appears to be divided in half in one of the Top, Front, or Right views.

If you select the sphere and use Trim on it, and pick the line as the cutting object, your result will be 2 half sphere surfaces that are not solid pieces, just the surface of the sphere "skin" cut into 2 pieces.

If you instead select the sphere and use boolean difference and use the line as the cutting object, you will get 2 solid fragments that have the plane of the extruded line incorporated into them.


One of these operations is not automatically "better" than the other, but basically Trim is a more "low-level" operation which works at a surface level.

The booleans are basically a wrapper around doing several things like an extrude, trimming, throwing away of different parts automatically depending on where they are located in the volume, then followed by a join. You can do all those operations manually using only Extrude, Trim, and Join, but that is kind of bundled up for you in one batch operation with the Booleans.

So if the booleans match what you want to do, you can save time using them instead of Trim since they bundle up several operations together.

- Michael