Use this dialog box to select surfaces you want to use to limit machining in a 3D feature. Check surfaces are surfaces that denote area that won’t be milled away. You should select surfaces that are more horizontal than vertical. The check surface acts as a boundary up to which milling occurs. With vertical check surfaces the milling will stop there, but may resume on the other side of the check surface if the surface to be milled extends beyond the check surface.
Select the surface(s) in the list box or click Pick and select a surface with the mouse. To pick additional surfaces, click Pick again before selecting each additional surface.
Click OK to return to the 3D feature properties dialog box.
Click OK and Apply to return to the 3D feature properties dialog box and apply your surface selection to the feature.