If I may share an observation with folks
>concerned about "all of that glueing": hot hide glue ...<
There it is, rearing its ugly head again...
>
>FWIW, Barnes suggested putting the dados into the register stock (dimensioned
>to the correct thickness), and THEN (believe it or not) cutting the blocks at
>the required angle. Has ANYONE ever done this? Clearly, my woodworking skills
>are too poor. I did make a pile of angled blocks, and dadoed them afterwards,
>but that felt far too unsafe-and, like they say, if it feels unsafe, then it
>probably is. . .
 No, nor it is anything I'm going to try. If, like me, you have one of
those wonderful cast-iron mitre boxs from the turn of the century, it is,
of course, feasible to do it safely. But what for? leaving the pieces
square, dado or not,  and too long leaves enough room for a clamp here and
there and overhang enough  to cut off on the band saw along the line. Plane
that side clean and cut parallel on the table saw. Or simply plane both
sides down if you prefer.
 
Hendrik's analysis of the Baker Harris guide is very good and seems to
coincide with what I have observed, too.  If it was a plow plane, it would
have to be a single-purpose plane with a skewed blade and side-cutters both
sides. This would mean a lot of registers to justify something that ornate.
I rather suspect from what I have seen (not Baker Harris), that the edges
were marked with a cutting gauge, perhaps with two fixed cutters giving an
absolutely parallel slot.(square edges as Hendrik says) and sawn to depth
with a then common special saw for sliding dovetails and the slot removed
with a router plane. In the case of BH, Hendrick migh tbe able to comment
on the endgrain surface in the slots.
regards, Bill
 
William Jurgenson
Keyboard Instrument Maker