Use the Bump 2d utility
For a description of the Bump 2D utility, see Bump 2d
To bump map layered textures using Provide3d Info
Map a 2D texture to a material's Bump Mapping attribute.
Map a 3D texture to one of the 2D texture's Color attributes (such as V Color).
Double-click the bump2d swatch in the Hypershade to open the bump2d's Attribute Editor and turn Provide3d Info on. Maya bump maps both textures.
To cascade, or stack, bump maps
In the Hypershade, create two 2D textures and a material.
Create a Bump2d utility node.
Middle-drag the first 2D texture swatch over the Bump2d utility swatch.
Create another Bump2d node and middle-drag the second 2D texture swatch over the new Bump2d utility swatch.
Middle-drag this Bump2d swatch over the first Bump2d swatch.
The Connection Editor appears.
From the Right Display menu, select Show Hidden.
From the Left Display menu, select Show Hidden.
Select Out Normal from the Outputs column and the Normal Camera from the Inputs column.
In Hypershade, middle-drag the first Bump2d utility swatch over the material swatch to assign both bump maps to a material's attribute.
Tip:
If you bump-map a material that uses environment maps, connect the Out Normal attribute of the bump node to the Normal Camera attribute of the Environment texture, as well as to the Normal Camera attribute of the material. Otherwise, the environment does not reflect correctly in bumpy areas.
Maya provides a MEL script that does this for you. After you connect the Out Color of the environment map to the Reflected Color of the material, type cnctBumpProjNormal shader-name in the command line (where shader-name is the name of the material).
To delete a bump2d map
Open the material's Attribute Editor.
Right-click the word Bump Mapping.
Select Break Connection from the pop-up menu.
(пара строк из хелпа)