Blender Documentation: Last modified August 11 2003 s68
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# Spin and SpinDup

The spin and spin dup are two other very powerful modelling tools.

## Spin

The Spin tool in Blender is for creating the sort of objects that you can produce on a lathe. This tool is therefore often called a "lathe"-tool or a "sweep"-tool in the literature.

First you must create a mesh representing the profile of your object. If you are modelling a hollow object, it is a good idea to give a thickness to the outline. Figure 31 shows the profile for a wine glass we will model to demonstrate this tool.

Figure 31. Glass profile

In EditMode, with all the vertices selected, access the EditButtons window (F9). The "Degr" button indicates the number of degrees to spin the object (in this case we want a full 360° sweep). The "Steps" button specifies how many profiles there will be in the sweep (Figure 32).

Figure 32. Spin Buttons

Like Spin Duplicate (covered by the next section), the effects of Spin depend on the placement of the cursor and which window (view) is active. We will be rotating the object around the cursor in the top view. Switch to the top view with NUM 7. The cursor should be placed along the center of the profile. This is easily accomplished by selecting one of the vertices along the center, and snapping the cursor to that location with SHIFT+S>>CURS->SEL.

Figure 33 shows the wine glass profile from top view, with the cursor correctly positioned.

Figure 33. Glass profile, top view in edit mode, just before spinning.

Before continuing, make a note of the number of vertices in the profile. This information can be found in the Info bar at the top of the Blender interface (Figure 34).

Figure 34. Mesh data - Vertex and face numbers.

Click the "Spin" button. If you have more than one window open, the cursor will change to an arrow with a question mark and you will have to click in the window containing the top view before continuing. If you have only window open, the spin will happen immediately.

Figure 35 shows the result of a successful spin.

Figure 35. Spinned profile

Now for the tricky part. The spin operation leaves duplicate vertices along the profile. Normally you can select all vertices (AKEY) and do a Remove Doubles operation.

In very rare occasions these duplicates might not exactly match the original profile. In order to remove them and thereby close the object, we have a choice of two different methods. Either raise the numerical value of the "Limit" distance below which doubles are removed (by default 0.001), or bring the vertices closer.

To do the latter, use the boundary select tool (BKEY) to select all of the vertices that lie along the seam. The white rectangle in Figure 36 shows the vertices that must be selected.

Figure 36. Seam vertex selection

Press PERIOD or the appropriate icon button to scale around the location of the cursor. We'll do this to scale the selected points into a line that passes through the center of the object.

Press SKEY to start scaling. Drag the mouse cursor vertically and press the middle mousebutton. If done correctly, this will constrain scaling operations to the Y axis. If not, you can MMB again to turn off the constraint and try again.

While scaling, hold down the CTRL key to scale in 0.1 unit increments. Scale the line of points down to 0 in the Y axis, and LMB to complete the scaling operation. If you like, you can revert to the default rotation/scaling pivot by pressing COMMA when you have finished.

Remove doubles in the current selection set by pressing WKEY>>REMOVE DOUBLES (Figure 37). A small box will appear saying how many points were removed. Dismiss this box by moving the mouse, pressing ESC or by clicking the LMB or RMB.

Figure 37. Remove doubles operation

Notice the selected vertex count before and after the "Remove Doubles" operation (Figure 38). If all goes well, the final vertex count (38 in this example) should match the number from Figure 34. If not, some vertices were missed and you will have to go and weld them manually. Or, worse, too many vertices have been merged.

Figure 38. Vertex count after removing doubles.

| Merging two vertices in one

To merge (weld) two vertices together, select both of them by holding SHIFT and RMB on them. Press SKEY to start scaling and hold down CONTROL while scaling to scale the points down to 0 units in the X,Y and Z axis. LMB to complete the scaling operation and click the "Remove Doubles" button in the EditButtons window.

Alternatively, you can press WKEY and select "Merge" from the appearing Menu (Figure 39). You can then choose in a new menu if the merged node will have to be at the center of the selected nodes or in the location of the cursor. The first choice is better in our case.

Figure 39. Merge menu

All that remains now is to recalculate the normals by selecting all vertices and pressing CONTROL+N>>RECALC NORMALS OUTSIDE. At this point you can leave EditMode and apply materials or smoothing, set up some lights, a camera and make a rendering. Figure 40 shows our wine glass in a finished state.

Figure 40. Final render of the glasses.

## SpinDup

The Spin Dup tool is a great way to quickly make a series of copies of an object laid out in a circular pattern. Let's assume you have modelled a clock, and you now want to add hour marks.

Figure 41. Hour mark indicated by the arrow

Model just one mark, in the 12 o'clock position (Figure 41). Select the mark and switch to the EditButtons window with F9. Set the number of degrees in the "Degr" NumBut to 360. We want to make 12 copies of our object, so set the "Steps" to 12 (Figure 42).

Figure 42. Spin Dup buttons

- Switch the view to the one in which you wish to rotate the object by using the keypad. Note that the result of the "Spin Dup" command depends on the view you are using when you press the button.

- Position the cursor at the center of rotation. The objects will be rotated around this point.

- Select the object you wish to duplicate and enter EditMode with TAB.

- In EditMode, select the vertices you want to duplicate (note that you can select all vertices with AKEY or all of the vertices linked to the point under the cursor with LKEY) See Figure 43.

| Cursor Placement
| If you want to place the cursor at the precise location of an existing object or vertex, select the object or vertex, and press SHIFT+S>>CURS->SEL.

Figure 43. Mesh selected and ready to be SpinDuped

- Press the Spin Dup button. If you have more than one 3DWindow open, you will notice the mouse cursor change to an arrow with a question mark. Click in the window in which you want to do your rotation. In this case, we want to use the front window (Figure 44).

If the view you want is not visible, you can dismiss the arrow/question mark with ESC until you can switch a window to the appropriate view with the keypad

Figure 44. View selection for Spin Dup.

When spin-duplicating an object 360 degrees, a duplicate object is placed at the same location of the first object, producing duplicate geometry. You will notice that after clicking the "Spin Dup" button, the original geometry remains selected. To delete it, simply press XKEY>>VERTICES. The source object is deleted, but the duplicated version beneath it remains (Figure 45).

Figure 45. Removal of duplicated object

| Avoiding duplicates
| If you like a little math you needn't bother with duplicates because you can avoid them at the start. Just make 11 duplicates, not 12, and not around the whole 360°, but just through 330° (that is 360*11/12). This way no duplicate is placed over the original object. In general, to make n duplicates over 360 degrees without overlapping, just spin one less object over 360*(n-1)/n degrees.

Figure 46 shows the final rendering of the clock.

Figure 46. Final Clock Render.

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