I think I need a bigger machine...

At 26" in length, the 235 valve cover mold is a bit long to machine in one piece. 

To make the mold, I lamitnated 6 pieces of 3/4" MDF.  This stuff machines super easy allowing for some pretty fast feed rates.  It took about an a hour to accomplish this.  That time could have/should have been less if not for quite a few wasted moves and air machining...