Michael, at times I'll try trimming a solid with a curve and end up with a hole in my solid?? The trim op will seperate the surfaces as I want but deleting the unwanted piece left the surface unclosed.


What I typically do then is extrude the curve into a surface or solid and then subtract...

Actually now that I'm typing this, perhaps I should have tried a boolean operation with the curves instead of a trim?

I usually think trim with curves and boolean with solids - I have to give this a try...

-Will

PS - DUHoid! That was it - boolean instead of trim! Boy knowing this would have saved me some time the other nite! :-P

THe other thing I think of Will is with bool dif it will punch through the solid. Using trim I can only select one side to remove. So on a sphere, a circle can trim a hole or punch a tunnel

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

Hi Burr, yeah basically another difference of Trim is that it dices up the surface and then lets you manually pick which pieces you want to remove or keep.

You can pick just one single cut piece to remove, which lets you do something like remove only one area where a projected circle cuts your solid to make a hole there.

Also with Trim you can cut everything up and leave all the pieces behind by pushing "Done" or doing a right-click instead of picking any pieces to remove.


Booleans are different - they are focused on automatically deciding which pieces to throw away by where they are located in the different volumes. Like a Union throws away the pieces internal to both pieces, Difference throws away the part that is only inside the subtraction piece, etc...


If you wanted to do a hole that did not go all the way through an object, you could still do that with a boolean but you would need to extrude the curve into a solid yourself, extruding it to the depth you want to make the hole and then using that extruded piece as the cutting object in the boolean rather than the curve.

When you do a boolean with a curve, the extrusion that it automatically produces always goes through the full length of the object.

- Michael

Many uses with the 2 tools. I had in mind from one of your tutes where you just wanted to "remove" 1 surface so you could do a blend.

So with the trim you could hit your sphere:



Then select "Only" the surface closest to your blend to be removed, to leave the opposite side untouched:



Select the edges for the blend:



And Poof! A good reason to leave open holes on the surface:



Burr