Problem with extrusion

[greenwoods1462]

sorry this is a basic question.  I have created a roof section for a coach that i have extruded.  I now want to create an iner pannel.  this is a rectangle but i only want to extrude the part below the roof.  I want to select the bottom half of the rectangle and the bottom of the roof and extrude.......but the whole rectangle gets selected.  Basically i want to select just the rectangle with the curved top.

I think that i need to add a constraint but this is not working.

Any help gratefully received.

[TheCADWhisperer]

Sketch2 is not needed.

Your Sketch1 is not fully defined - so I am not certain of your true Design Intent, but see Attached file.

[Intuos5]

Do you mean something like this?

In your second sketch, you want to could project roof curve into the second sketch with the rectangle. Alternatively, you can extrude the entire rectangle and then chop off the top part. The second method is in a new component.

[greenwoods1462]

thank you.......this is what i need....i have done a few of these and they have worked.  I have downloaded your file but i am struggling to understand why my original will not work.

Sorry to show my ignorance but you suggest that sketch 1 is not defined......but how could i have extruded something that was not defined.....

You say that sketch 2 is not needed but it must be needed or else i cannot get the rectangal below the roof.

I really want to understand where I am going wrong as it feels like i am making a basic error....

many thanks in advance.

[TheCADWhisperer]

I did not use Sketch2 in the example that I Attached, I used Sketch1.

Fully defined sketches turn black (or some other dark color depending on your environment setup).

This is the most basic, foundational concept in an parametric CAD program.

You give all of the information to reproduce your Design Intent so that anyone could reproduce.

A fully define sketch is easier to edit and less likely to inadvertently create unintended geometry.

White dots and blue geometry is underdefined.