Jean noticed what should have been obvious to me, too: the patent drawing is different from the "real thing". This made me read the patent text more carefully - and it turns out that the machine in the drawing probably was never built. It is couched in some complicated language, but essentially the text says "this is one possible construction".
Last, in the text, are three patent claims (is that right? "patent wishes"?) - 1) a tabletop mangle with a lower roller lifted with help of a two-armed swiveling lever and a spring, 2) same as 1, with the addition that the two-armed lever is angled and 3) same as 1, with the addition that the arm which connects with the spring is longer than the other arm.
Here are a couple of detail pictures:
How the spring is mounted:
The rollers (and the "swing", or two-armed swiveling lever) exposed:
And now we all can see that the actual construction is even more different from the patent... And, yes, it is the right patent, because the patent number is written on the side piece:
As for "apron" or no apron - I don't know. Before the mechanical mangle, there was the roller and the "plank":
(for many fantastic carved boards - they were often very decorated - go here)
Anyway, from what I have read, these were used either "as is" or with a special "mangle sheet": roll the cloth (with or without the protector) as tightly as possible onto the roller; grab the board, lean hard on the board and roll in the same direction as the cloth had gone on; when you reach the end, slide the roller back towards you; repeat.
Next came the box mangle - like this or this (or, for the scary pictures, this!). From what I understand, one of the ideas with the mangle sheet was that you could load several smaller pieces in one go - but I think that it also helps with the "sheen".
All the older "small" mangles with the big spring on top I have seen have been without apron. Come to think of it, mine may be one of very few having the apron.
All modern mangles have it, though.
As for adding one: I think the important bit is getting the roller smooth again - no ridge, no screw heads...