Darren,
Definitely. Once you get the concept of creating the 3D parts first then letting the computer generate 2D drawings from that geometry, it's so easy to go back and change things. I've said before, I've used Pro Engineer and we use Unigraphics at work but Alibre is much more intuitive than those.
Quick example, for the engine shown in the PDF I must have dropped a boo boo last time I revised the parts. When I assembled it together last night I noticed the piston was sticking out of the top of the cylinder slightly when at TDC. My immediate thought was that I'd designed the con rod too short. So I flipped to a view from the back (cyldinder side) of the engine, set the crank to bottom dead centre (if you constrain the parts properly in an assembly you can actually turn the assembly over as you would in real life). Then I surpressed the cylinder so I could see the innards, at which point I could confirm with the measuring tool that I had indeed drawn the con rod too short. I measured from the bottom of the piston to the cylinder cover and it was 3/32", not the 1/32" I had intended. Set it back to TDC and it's sticking out 1/16", therefore I've made the connecting rod 1/16" too short. So went into the con rod part, extend the middle section by 1/16". If you have the settings right, the 2D drawing automatically updates as does the assembly. Job done!
With 2D CAD a boo boo like this isn't likely to be found until you have made and assembled the parts together!
If you're thinking about it, don't, just go for it at this price, you definitely won't regret it. I can't see this price lasting too long.
Nick
ps can feel my

getting stronger. My next project was supposed to be an electric loco, then a flame gulper, then an ic engine. My 3 year old keeps hassling to get my 3 1/2" gauge Mabel up and running though and a 4 1/2" scale simplicity roller! I keep thinking of other engines to make though, this is not good, at this rate nothing will get done!

Sorry
