I'm surprised to see myself writing this, but free software isn't always better. I've used many, many software programs to generate vector-based drawings. AutoCAD, CorelDRAW, Sketchup, Draftsight, SmartDraw, Illustrator, and probably a dozen or so that I've forgotten.
I realize that most hobbyists don't have access to the high end 3D cad packages that are used in industry these days, but most of the time they are much quicker to use to generate drawings that consist of more than a few lines and arcs. The best thing is that a well designed parametric model (like those made in SolidWorks, Inventor, and the like) can be changed and everything else adjusts accordingly.
Say, for example, you have an engine that you've drawn in 2D CAD. The piston is there with the connecting rod inside a cylinder. Now you want to increase the diameter of the piston by 0.010", and the length by 0.125" ..... oh boy, look at all the things that need to be erased, moved, little lines drawn in there to join everything back together, lines trimmed, extended ..... wow, why didn't I just draw the damn thing on paper??? I guarantee after you become capable using a 3d parametric modeling package you'll agree with me.
Bear with me for just a second before you start cursing "YES, I KNOW BUT I CAN'T GET OR USE THAT SOFTWARE" and read on. I'm willing to donate a bit of my time and skill to those who would like drawings and/or models made of various things for NON-PROFIT PERSONAL USE. I can work from sketches, good written descriptions, sometimes pictures and I can even guess missing dimensions in some cases. The more information I have to work with though, the better the result.
Of course, it would be on a first-come, first-serve basis and my time is limited so you'd need to be patient. Depending on how it goes, I'll have to decide later for how long this offer stands. All I ask in return is that I am given credit where credit is due. For commercial use, we'd have to discuss terms. I've never used the PM system here, so it would be better to email my username here @gmail.com if interested.
Samples attached
-Sparky (Brian)