Working on an 1894 Queen Anne in Keene, I’ve got 14 original 1 3/8" sash with wavy glass; rails are tired but sound — do you stabilize with consolidant and dutchmen or mill new to match? I’d rather preserve every tool mark and stick with linseed oil putty and hide glue, but where do you draw the line before a remake, especially when a meeting rail measures 5/16" at the lock?
I save them by kerfing the meeting rail from the inside and gluing in a quarter-sawn pine spline with hot hide glue, which fattens a 5/16" edge without touching the exterior profile; oil it with a 50/50 linseed/turp wash before putty. Are the lock-side tenon shoulders still crisp, or are they crumbly? If the shoulders are gone or the hinge stile is punky past the pin holes, I replace just that rail and keep the wavy glass; Leeke’s walkthrough is solid: https://historichomeworks.com/hhw/.
Building on @elsaJ45, I’d save them: laminate a 1/8" boxwood (or QS white oak) slip onto the interior meeting edge with fish glue, plane flush, and hit the joint with a quick dewaxed shellac wash — it’s like giving the rail a new lip without a facelift. Remake only if the horns and tenon shoulders are gone; are your horns still intact?
I’d tighten the joints first: pull the old pegs at the meeting rail, ream a hair, and draw‑bore in new riven oak pins with a slight offset so your 5/16" build stays put instead of popping later. @KeeneRestorer, do the original pins still bite or are they spinning?
At ‘5/16" at the lock’ I’d keep the wavy glass and glue/pin a thin applied astragal on the interior lock edge, then plane it in; it restores thickness, improves seal, and is fully reversible. Would you tolerate a discreet applied piece on an 1894 Queen Anne in Keene? Interior storms will take load off the sash so that repair holds.
Save them: kerf the inside face of the meeting rail and let in a 1/16" brass spline with hot hide glue, then plane flush; it discreetly stiffens that skinny section and gives the lock screws something to bite… I pair that with spring bronze and a tight interior storm so the sash does less work; if a rail’s lost about 30% section or the mortise is mush, that’s my remake line. @garyP88 ever try a brass spline on sash?