Why does a guy machine his own velocity stack when he could just buy one?? Some of us still BUILD our airplanes, too. It is cheaper to go buy an arf but we ENJOY flying something we MADE. I suspect that some guys machine things just for the enjoyment and from the feeling one gets from making something. I have a friend that makes his own engines. He could go buy one but he likes making his own. I machined a C/L venturi for one of my R/C engines when I could have bought one from OS. Why?? because I COULD. I have a 6 inch South Bend and I make a lot of things on it that I could just buy.