Well done, all. Yes, it is of course the making of a grand piano - and The Omniscient Mussel is spot-on. They are bending the frame and clamping it in place.
I took the photo during a tour of the Steinway factory in Hamburg on Monday. Lots of good pics, so I will put them on Facebook as soon as I have a spare moment. The reason for the trip will become apparent in due course!
Love the captions, glad I decided not to give a prize as I wouldn't be able to choose!