Double seaming machine @museum.de

The double seaming machine is a marvellous invention! It combines several operations into one and makes the metal roofer's work a lot easier!

If you look at the model roof, you can easily see the raised edges of the metal sheets: one side is about a centimetre higher than the other. Next, the higher one is placed over the lower one, joining the two. Both are now folded so that they form a single longitudinal seam, a standing seam – which is rainproof and durable.

All that repeated bending can, of course, be done by hand, though it requires quite an effort. You'd use a hammer and a crimping seam iron. Or you can use the seaming machine, place it on the edges and simply lever them closed.