should be no contact of the coated exterior of the core 12 with any other surface the oven is maintained in the range of 345 u00b0 plus or minus 5 u00b0 for a time of 16 to 18 minutes following this heat exposure the roller is removed from the oven and hung for cooling following temperature reduction to room temperature the coating is removed from the non primed surfaces such as the end caps 314 and the axle shafts 316 at this stage the plastisol coating 318 exhibits a smooth surface which is unacceptable for use in a pre stretch system in order to prepare the surface of the coating 318 the axle shafts 316 are mounted on the center line in a lathe such as a 5c collect lathe drive with a 1 inch tapered roller in a tail stock adapter the outer diameter of the coating 318 is then turned to reach the desired outer diameter it has been found that a speed of 360 revolutions per minute and a feed rate of 0 030 inches is acceptable for this purpose as the smooth surface is stripped by the lathe from the roller it can be seen that an underlying porous cellular structure of the coating 318 is revealed the machining process provides a cellular coating thickness of at least 1 8 inch and preferably of 1 8 inch to 1 4 inch cylindrical in shape and coaxial with the rotation axis.