Hi, can anyone help me why i cannot trim my outer surface just like in picture below i am trying to do skateboard board. I keep re-sketch my drawing overthought it is fully define its still cannot using the trim surface feature.
The trim surface command is used to trim surface features. Your model consists of a solid (extrude-thin1) and a curve (which you don't really need). You don't have any surface features in your model which is why the command is greyed out.
Delete the curve feature, but keep its sketch. Then use that sketch in an 'extruded cut' feature. It will default to cutting away the middle of your deck, but if you click 'flip side to cut', it will cut away the outer portion.