Hi All. Me again :)

Don't know if this is a problem or not, but normally when I create an STL from a model that's been joined into a single solid , I only get triangles on the visible surfaces.
i.e

this is a section of the top of a shield, on which I've boolean union a solid I created from surface created with ZSurf. The shield and zsurf solid have joined nicely.






On this one model the the STL out put has also created the original un-trimmed surface of the ZSurf created surface. , see how there is a second internal surface?



This is what the solids looked like before the Bool->Union. You can see , I've trimmed off the base of the original ZSurf. (eagle), It's like the Bool-Union is recreating the trimmed surface internally?



I have attached the 3dm files , eagle-gray03 has 2 solids before the union is applied. eagle-type-2-cufflink02 is after the union. I've tried looking for points crossed over, but there are some many points, does anyone know of a simple method of checking a surface for defects?