Many cabinetmakers build jigs to speed up repetitive tasks. Installing thread escutcheons could well be a candidate for this approach. I have never been a jig enthusiast, either I'm too lazy or because I have seen too many craftsmen design work to suit existing tools, cutters and jigs rather than the other way around.
A thread escutcheon is a short keyhole shaped brass tube that is set into a matching mortise. Our thread escutcheons are cut from long extrusions of the required section and are very consistent. Old escutcheons were usually sand-cast and would vary significantly. Cast escutcheons are usually slightly tapered in section and are pushed into their mortise until tight. Extruded escutcheons have constant section and require precise fitting.
The keyhole profile consists of a round upper segment and a flared lower segment. To make life easier the round part of our escutcheons match common drill sizes. Brad point or Forstener bits are a must for this job. Regular drill bits will wander and leave ragged torn edges. This hole can be drilled through into the lock mortise or if you like it can be stopped at a depth just short of the escutcheon thickness and a smaller hole drilled on through for the key shaft. The escutcheon is then laid in place over the hole and with a knife the lower half is marked. Remove the escutcheon and cut these marks deeper. It is possible to use a router with an 1/8" or 3 /16" straight cutter to waste away most of the remaining material but the risk of irreparable error is significant. It is probably better to set the router aside and drill a hole in the middle of the mortise. Then with a 1/8" chisel bring the mortise out to the mark lines.
Having assured yourself that the escutcheon will fit it can be pushed into place. Make sure the fit is not too tight as pressure will force the sides in and create gaps. It is a good idea to slightly bevel the leading edge of the escutcheon. If you do this there will be less likelyhood of damage to the sharp edges of the mortise when fitting. Any damage to this area will show up as darkened wood when finish is applied and darkened wood is often mistaken for wood filler.
With a little glue applied to it's edges the escutcheon can be pushed into place. Set a small block of wood over the escutcheon and with a "C" clamp press it into the mortise. The block of wood will keep the escutcheon straight and will also prevent it setting below the surface. Ideally it should sit a hair above the surface and be filled or sanded flush.