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The Rip tool lets you tear out a hole, such as a mouth or an eye socket if you're modeling a face, in your mesh. You can use the Rip Tool in either vertex select or edge select mode. The Rip Tool does not work in Face Select Mode. You can also use the Rip tool to do split apart a mesh, for example, splitting a sphere into two halves. You can create faces to join the parts of the mesh that you have ripped. The goal of this tutorial is to make you comfortable both ripping a mesh apart to create holes where you want them, and to join mesh parts together again.
We'll start with the default Blender 2.49b scene. Delete the default cube (press the Delete key and press Enter to confirm). Add a plane (Space - Add - Mesh - Plane). The plane is in Object mmode. Scale the plane to 4 times its original size (S - 4 - Enter). Get rid of the 3D Transform Manipulator to make the demonstration of the Rip Tool easier to follow.
Press Tab to go into Edit mode. Press the Edit buttons (F9) and click the Subdivide button 3 times. Press the A key to deselect all vertices.
Look at the indicators for vertices, edges, and faces. Right now, the plane has 81 vertices, 144 edges, and 64 faces. The zeroes show that nothing is selected.
Make sure you are in Vertex Select Mode (Control - Tab - 1) or the Vertex Select icon. Position the 3D cursor below and to the right of the vertex you want to select. Select the vertex, then press the V key, grabbing the vertex to the right. A hole is created to the right of the vertex. Look at the indicators for vertices, edges, and faces. Before the plane had 81 vertices, of which none were selected. Now, the plane has 82 vertices, and one is selected.
This gives a clue as to what the Rip tool actually does. It creates a duplicate vertex at the same spot as the selected vertex, connected to the vertices as the copied vertex. When the mesh is ripped, that vertex drags the adjacent edges with it. The 3D cursor position determines the direction of the rip.
Press Alt-U, which brings up the Undo History. Click on Select to undo the rip. Now we're back to having the vertex selected, with 81 vertices altgether. Move the cursor above and to the left of the selected vertex. You can constrain the rip to an axis. To do that, press the V key, and then the Y key to constrain the rip to the Y axis. Press Enter to confirm. So you can see that the direction of the rip depends on the position of the 3D cursor at the time that you press the V key. The rip is along the edge that is closest to the selected vertex.
Press the A key to deselect the vertex. Go to another part of the plane, and select a vertex. Then Shift select (Shift - Right Click) the vertex immediately to the right of it. Position the 3D cursor above and in the middle of the selected vertices. Press the V key. You now get a bigger rip, a trapezoid, with 2 vertices on top and 4 vertices on the bottom. So a rip with N selected vertices produces a ripped polygon with N vertices in the ripped direction and N+2 vertices in the original direction.
If you start the Rip and then immediately decide not to continue, the new vertices still remain. To illustrate this, select a vertex, press the V key, and then press Esc. The vertex created by the Rip tool is still there. You can rip the mesh now even though you pressed Esc. Press the G key and move the vertex and the mesh is ripped. Press Enter to confirm.
Press the A key to deselect all vertices. Suppose you want to patch up the hole that you created. The solution is to select the vertices for the new face (3 or 4) and press the F key. To illustrate this, select the 4 vertices that form the square of the hole created from 2 selected vertices. Press the F key. A face is created.
Press the A key to deselect all vertices. Now we'll create triangular faces for the remaining two holes. Select the 3 vertices forming the left triangle, and press F. Press the A key to deselect everything. Select the 3 vertices forming the right triangle, and press F. The hole is now repaired. Press the A key to deselect.
Ripping via an edge loop is a great way to split a mesh. Select an Edge Loop by positioning the 3D cursor on an edge and pressing Alt-Right Click. Then press the V key and scroll down. Press Enter to confirm. You have now split the mesh along the edge loop.
Rip works in edge mode as well. Go into Edge mode, by either selecting the Edge icon or pressing Control - Tab - 2. Position the 3D cursor above an edge to select. Select the edge (Right Click on an edge). Press the V key. The rip works just like selecting two adjacent vertices, which is, of course, what constitutes an edge.
Press the A key to deselect everything. You rip on two edges along the same loop. Select an unselected edge. Then Shift Select (right click while holding the Shift key) to select the edge next to it. Press the V key. The rip works in the trapezoidal fashion you would expect.
Rip works on other meshes as well. Let's look at a UV Sphere. Press tab to go to object mode. Click the second square to go to Level 2, so we have a blank 3D viewport. Add a UV Sphere (Space - Add - Mesh -UVSphere), accepting the default of 32 rings and 32 segments. Press Z to go into wireframe mode. Scale the UVSphere 3 times (S - 3 - Enter). Press Tab to go into Edit mode. Go into Edge select mode (Control - Tab - 2). Press the A key to deselect everything.
Press Num 1 key to go to front view. Position the cursor on an edge and press Alt-Right Click to select an edge loop. Position the 3D cursor below the selected loop. Press the V key. Move the selected edge loop down. Behold, you have split the UV Sphere. Press Z to go into solid mode so you can see.
Ycu can also rip and scale at the same time. Select another edge loop (Alt- Right Click) for splitting the UV Sphere. Position the 3D cursor below the loop. Press the V key, then the Z key to constrain along the Z axis, drag the edge down. Press Enter. Then press the S key to scale the loop.
I hope this gives you a good idea of the Rip tool, which is very handy for creating holes in a mesh. Happy Blendering!