Hi fiatnm,
>> I wish to know what Break Link is doing behind the screen.
So when we project geometry, a link is created and the projected entity ( in this case a circle ) updates when the original geometry updates. But when the original geometry is no longer available, the projected geometry is "orphaned". Inventor gives us an error, and allows us to fix the sketch. Using the Break Link option makes the entity (again in this case the circle) independent, so that it behaves just as if you'd sketched it, rather than projecting it.
>> I follow your advice of 1st simple sketch and building on that and it is working well. Before I have to struggle many hours and many steps to get fully constraint sketch, now I can get it with a couple of steps.
Indeed the simple sketches method is extremely powerful, for beginners and experienced users both. When working in an office of professionals you are often required to update or modify someone else's work, and it can be very difficult to do when that work was created using sketches that contain geometry that controls multiple features. For that reason we prefer to see designs create models with the idea "how can model this so that someone else can update it quickly". Thinking about this as you model, saves time (and money) later.
>> Thank you very much for introducing simple method.
You're quite welcome, but I should point out that just as I have introduced this to you, others introduced it to me. I worked for many years using AutoCAD and am very proficient in that software. In it we "draw" rather than "sketch" and when I began using Solidworks and then Inventor, I was guilty of trying to draw complex sketches those softwares. Once I learned to use simple sketches, I was able to progress quickly learning the rest of the software since I didn't get stuck trying to create and modify sketches.
>> I have given a name for your method KISS (Keep it Simple and Stupid) approach.
I understand what you mean, as when we "dumb" down our sketches, it might make them seem less intelligent, since there is less information contained in them. But, I would say: Keep it Simple and Smart! , since when sketches begin to act stupid, it's often because the are not simple. Keeping them simple, keeps them acting smart.
Also, traditionally the KISS method means (Keep it Simple, Stupid!) , but in a professional business atmosphere the word "stupid" can be received poorly, offending others, and making them defensive, even when used as a joke, so we try to say (KISS = Keep it Simple, Sir!)
I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com