This invention relates to building construction elements such as siding or paneling and more specifically to those of the type having a core or backing of foam polymetric material on an vinyl cover. 
Various construction elements for buildings and the like comprising a vinyl covering with a low density foam of polymetric material disposed on a surface thereof to form panels, siding, beans and the like are known.  The most limiting factor which prevents their more widespread use is the problem of delamination of the foam material from the vinyl covering as a result of impact, ageing or environmental influences such as temperature, moisture and the like.  Because the foam plastic material will normally not bond to materials such as vinyl, methods have been devised to mechanically lock the foam material to the vinyl. 
U.S. Pat.  No.  4,304,080 discloses one such means which comprises plurality a of spaced-apart tabs which extend longitudinally of the vinyl covering and are extruded or otherwise formed with the vinyl covering itself.  This formation of the vinyl covering and projections are extruded through what is known as a "profile die".  While vinyl covering has the required final shape or cross-section as it exits a profile die, this type of extruding is very slow and thus unsatisfactory when high production is desired.  High production is achieved by extruding the vinyl covering material through a "sheet die" and then forming it into the desired shaped by passing it through pinch rolls which is commonly known as "post forming".  During this "post forming" operation of the vinyl sheet extrusion, embossing of the outer surface of the covering to impart a simulated wood grain or other effect can be done.  As can readily be seen, with the locking rib disclosed in the aforementioned U.S. patent protruding from the back of the extruded vinyl covering, no post forming or embossing is possible because such ribs prevent the passage of the covering through the required pinch rolls. 
Applicant's novel method comprises the gouging or cutting of a plurality of arcuate-shaped projections from the back or inside surface of the covering after all post forming operations have been completed thus enabling the higher speed "sheet die" extrusion method to be employed.  In addition, because Applicant's projections are arcuate or curved in shape, a considerably better mechanical lock between the vinyl covering and foam material is achieved than by prior art means and one that will resist delamination irrespective of the direction an impact is applied, which is not the case of the ribs that are extruded in that they are parallel to each other and normally extend in the same direction. 
It is therefore the primary objection of the present invention to provide a superior building construction element together with the machine and method to manufacture it. 
It is another object of the present invention to provide a novel means to mechanically lock the vinyl covering to the plastic foam material together to resist delamination by environmental influences or forces applied there to in any direction. 
It is yet another object of the present invention to provide a novel method of forming a locking projection on the inside surface of the vinyl covering which enables the covering to be extruded more rapidly by means of a sheet-type die and post formed and embossed by passage through pinch-type rolls. 
It is a still further objection of the present invention to provide a novel, simple, inexpensive apparatus for forming the locking projections on the inside surface of a post formed extrusion. 
Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and accompanying drawings, which are merely illustrative of the present invention.