Tool planes / Construction planes

[MIL-TFP-41]

Just a quick question bout these.

When would these be not equal to each other in a toolpath? I have been programming 5 axis for a few years now and my typical planes configuration (in 3+2 mode) would be WCS=TOP, Tool Plane=A-90, Construction Plane=A-90

 

I have actually had my sphincter tighten up like a Kurt vise once when I missed making the T-plane and the C-plane equal...Never have I had a situation where the planes would not be equal.

 

anyone?

[MLS]

Yes, I tried it a couple times.

 

I did some project toolpaths normal to a c-plane while on a different locked t-plane.

 

It worked but it made me nervous because I was taught to never ever do that.