Starting a new thread from one yesterday because I'm having some new trouble trying to get a simple cylinder to dxf out properly and I'm not sure if I'm going about the process the correct way.  The original question of pipe intersects was answered in another thread by some kind people.

After reading alot on here and youtube videos about the best way to model a simple rolled sheet metal cylinder, I've see that many people do it different ways.  Some people start with the sheet metal base flange option and use the centerpoint arc to a 359 deg segment to draw the cylinder and extrude it to whatever length.  Then others will draw a complete circle and then break out a segment so its not connected and use the feature extrude, then later use INSERT BEND to make it into a sheet metal part.  Just trying to figure out the quickest way to draw say a 24" diameter pipe x 1/2" wall and make it into a sheet metal part that can be flattened and dxf'd out to a file for flamecutting.  What I was trying for was actually an 18" pipe going into 24" at 90 degree then using COMBINE to subtract the smaller pipe cutout from the main pipe at the intersection point to get the cutout in main pipe.  This worked but I notice if I do steps in wrong order, sometimes COMBINE is grayed out for some reason.

Lastly, if I'm doing all of this correctly, I can flatten out the part on screen, but when I go to DXF output options, once I choose "sheet metal" and "geometry", I never get the entity graphics in smaller screen showing what's gonna be outputted.  For simple sheet metal parts with a small bend (not the rolled type), the dxf option works fine.  Not sure if I have a glitch with this SW2010 sp0 or not.