After a recommendation on here, I have downloaded Solidworks. I have gone through a mountain of training vids and I am doing really well with it so far considering I have no CAD experience (I have managed to do a full assembly of a versatile dividing head in less than a week).
The only things I am struggling with is adding threads to holes or rods etc.. I have found the nuts/bolts and other fixings in the toolbox but other threads are still a mystery. So far I am just using plain faces to create assemblies, and I cannot find DP spec gears - only Module.
If anyone can point me to some further training to help me sort these niggles, I will be well on the way to mastering all I need to know - for now.