Jim nailed it. Even for the 3d printing guys, it's all based on ROI. First I have to research (find pics & measurements, or even drawings w/ Dimensions of the stuff if possible), then modeling the components into 3D can be time consuming. Just for the fun of it, I uploaded (to Shapeways) an assembled helper/pusher axle, we'll say it took me 20 hours to model in 3D and make it 3D Printable. So, based on a Median wage of 50k/yr for a CAD designer... that's about $25 per hour. that's $500 I need to recoup, on something I don't know how well it'll sell. For the sake of time I uploaded it fully assembled.... the Shapeways cost alone is $45. Where do I set my break even point? 20 units? how many people are going to spend $70 on a Helper/Pusher axle?? Even if I only charge say $10 per hour..... the cost per is still $55 based on a 20 unit break even point.