Hi Juraj, a parametric based modeler would work better for these kinds of tasks. MoI is more focused on making things quick and simple to draw initially. In a parametric type CAD system there tends to be more steps involved to just draw things but your steps are remembered and can be adjusted.

> 1. Can I select the surface and draw onto it?
> so far I noticed that I will always draw on zero height whatever view I have and not on the surface.

If you have object snap enabled then the first point you pick will go on that snapped-on-to object's height.

For your case here since you already have circles at that height it would be easiest to use those, either select the circle edges and duplicate them using Ctrl+C/Ctrl+V and then select one and modify its radius value in the properties panel, or use Construct > Offset to make a new circle.


> 2. Can I adjust hole sizes of the 4 holes in the corners?
> Again, way I can come up with is quite complicated.

To make them larger you'd make a larger circle and then do boolean difference. To make them smaller you'd need to do an "untrim" to remove the holes and then do a new boolean. http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4


> Atached model is quite simple so it's easyier to see operation, but more complex
> models will be real pain doing above mentioned.

MoI is just not the right tool to use for a complex assembly that will need those kinds of modifications later on. You would want to use a parametric CAD modeling system for that type of job, there are many of them out there. MoI is focused on different kinds of things than that.

- Michael