Starting with this lathed part with cut-out, I want to cut off a planar section from the part. Specifically, my goal is to produce a part that I can throw at a 3D printer -- an Ultimaker -- and, thus, I need the part to be relatively hollow, but with a well defined filled thickness (Hence the custom inner lathed surface shape).

Coolio; worked well so far and I've duplicated the original part I'm trying to customize well enough.

Now I need to cut a planar section off one side. In particular, this is the bottom cap to a shower head slider pole and it sits in our shower in a spot where the door *just* barely hits it.

The door will no longer hit it if I cut off a planar section that runs from the peak of the part to just below the side on a plane that runs parallel to the Z axis (that almost makes sense; effectively, a plane that is 45 to YX, running parallel to Z?).

Hrm -- I'm the first to admit that might vocabulary is far, far, far from accurate and, please, point me at some learning tools! To put it more generically, I want to cut a planar section out of the part whereby that planar section creates a flat face on the outside while maintaining a thickness of material on the inside (where the thickness doesn't matter that much).

I have attached the model file (also available at http://friday.com/Model/EndCap.vc3), if that helps.

Eventually, I'm also going to add a wash cloth hook on the other side. As well, I'm going to add a wash cloth hook to another variation of the same thing. Overall, the goal is start producing custom one-off pieces to solve various problems unique to our house and our living style in an attempt to make casual personal manufacturing a reality (using a personal 3D printer; in this case, either an Ultimaker or a Printrbot).