: what do people use on sharp inside curves?

When I did inside curves I used the front wheel of my belt sander, but you are somewhat restricted with how small a radius you can get into there. ?? Other than that, a good file will work.

: as panels are stacked back to back( or is front to front best?), is the
: orbital better on tearout as one panel will have more likelihood of tear
: out than other??

When I have cut out panels ( mirror ) I put the faces together on the inside. Most panels are fairly narrow, so I would clamp a board down the length of the area I was sanding within an inch or so of the edge being worked on and that keeps the pieces together fairly well. I got no tear out on the inside of the bundle. With the belt sander, I didn't get any on the outside either, but again..... refer to first answer.

: is the orbital lousier on sharp curve than a regular jigsaw?

When I cut out my panels with the jigsaw, I also clamped around the outer edges with my spring clamps and removed them as I went, and replaces them when I was past that point. Every few feet I put a C-clamp to really hold the two pieces together and keep them from shifting. If cutting out a panel from a whole sheet, I put a few screws through the plywood, where they would not be in the panels I was cutting out. Takes a bit longer, but you get good true mirror side panels.

I cut 1/8" from my lines and then clamped them together and started sanding with the front of the belt sander. Worked very well.

Oh, the panels were always laying down on the side, clamped together and I walked around them with the sander on it's side. With 3mm or 4mm plywood, it goes pretty quickly.

Hope that helps !!

Rehd