Hi Bob,
I use AutoCAD, but only because that's what I have at work!
A friend has been using FreeCAD, (
https://www.freecadweb.org/) which he says is easy to use. And like the name suggests, it's free! Attached a couple of snapshots of some hand pump valve parts off his Bedford MWC that he sketched up. Certainly looks impressive; I probably need to spend some time having a proper look at this software.
Owen.