I have a 1930s semi with all the original woodframes and single-pane windows. Every window is an (opening) casement, apart from a few which look just like the adjoining real casements, but are in fact fixed in place (non-opening, no hinge). I currently have no idea how these frames of these "faux casements" were attached (i.e. to the fixed frames) when the house was built. I doubt very much that any screws will have been involved, but it is possible nails were. Did they use glue for this purpose in the 1930s? I have no idea. To improve the insulation in this house I am about to replace all panes with vacuum glazing panes. Because of the extra thickness of these I need to remove each casement frame, remove the existing pane and do a fair amount of work with a router to accommodate the vacuum glazing pane. But I'm puzzled how I might go about removing these non-opening frames: I suppose I could try drilling (with a thin bit) a very large numer of very small holes all the way around and then use a very fine, thin, long chisel of some kind. But I'm wondering whether a suitable power tool exists. It would obviously have to be quite gentle (variable power), and at the same time capable of cutting deep into the wood to separate the inner frame from the "official" fixed frame to which it is currently attached.
The glazier can make you stepped units that will fit into the existing rebates with the second pane inside the opening, but you will see the border of the units.