the bond between the main steel roller body 46 and plastic outer covering 50 causing failure of the bond once the bond between the main steel roller body 46 and plastic outer covering 50 is broken the overall performance of the roller 42 may be detrimentally affected leading to premature failure of the roller 42 or unsatisfactory operation of the roller 42 it should be noted that unlike plastic covered rollers although all steel rollers are quite capable of handling heavy loads all steel rollers may not roll as desired when under light loading conditions as previously set forth fig3 illustrates a bi material roller 62 according to the present invention which solves the problems of the prior blasthole drill rollers and other problems associated with other rollers the roller 62 may be attached to the rotary head 34 shown in fig1 in a suitable manner the roller 62 is adapted to support a load and is rotatable about axis 66 which travels through a shaft 70 illustrative views of the roller 62 supporting different loads are shown and further described with reference to fig4 and 5 below the roller 62 includes a main roller body 78 which includes a first substantially non deformable generally cylindrical outer surface 74 located radially outward with respect to the axis 66 preferably the roller body 78 and thus the surface 74 are made of steel in the illustrated construction the main roller body.