Extend sheetmetal 45 degrees in a corner

[csongor.varga]

I am creating an open box, and want to add a U profile sheet metal on the top to hide the structure and my welding (of the structure).

I want these two white sheet metal parts to meet in 45 degree, so I can weld the gaps and grind it smooth.

I am not sure how to do that. I assume I need to unfold or create a flat pattern and extend it with a 45 degree triangle. I tried a few ways, but nothing works. Can you give me a walkthough what functions to use here?

[TheCADWhisperer]

@csongor.varga 

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

[csongor.varga]

f3d is not an option for me. The entire drawing in f3z is over 100MB.

I exported the sheet metal part in question to step format. See attached. 

Should I create a 45 degree construction plan and use the push-pull to extend the side of the profile to 45 degree?

[csongor.varga · Accepted solution]

Actually, I think I found a workaround:

First I extended the sheet metal part all the way to the biggest extent. Next I unfolded it, and I draw an outline on a sketch that I cut away with the Extrude tool. And I refolded the object.

Basically it was easier to delete away material in unfolded mode than to add to it using any other way. I think it will be close enough and if it does not fit propely, I can hack it with the angle grinder.