Work surface keeps changing unexpectedly.

[Jaeger1787]

Good day, Folks.

I am having difficulty in sketching on a chosen worksurface. 

The coach I am working on has asymetric window and door positions, so I can not simply cut through from one side.  Having created one side, I am now trying to sketch the windows on the other side of the coach.  I find that when I have apparently created the windows, some of them have been sketched on the 'inside' of the opposite coach side as shown in the screenshot.  There seems to be no consistency in this, it seems to occur randomly and I have no indication of the change until I try to extrude the window apertures.

How do I 'lock' a surface for sketching so that a surface behind it does not become the worksurface, or is there some easy method of moving the sketches to the correct surface.

I attach the file for comment.

Thanks. Keith

[jhackney1972 · Accepted solution]

A sketch will not move off of the surface or face it was created on by itself.  I will give you the answer to your second question first in the video and then try and explain a different modeling technique since you are modeling on a curved surface model.

[Jaeger1787]

Thank you Sir.

I think I have got the hang of your advice.  I have a problem in that sketching on the centre plane, is OK for one side, but as the sides are not mirrored, I think I need to construct an off-set plane to sketch the elements of the second side.  Also, before the windows are cut all the way through, there needs to be a shallow recess, making it a two-stage process.  However, I will watch the video several times until it penetrates and I succeed.  It seems that the initial problem was that selecting the plane to work on was hit or miss.

Thanks again.  I have accepted the solution.