> So it's a scraping tool, not a chopping tool. That's probably why it's cutting
edge is nearly perpendicular to the end of the chisel.

I wouldn't call it a "scraping tool."  There are two forms of lock
mortise chisel.  The more modern form is like this one.  The image shows
how to use it.  The older form works the same way. but usually has a
sharper edge. 

http://toolmonger.com/2007/12/10/get-bent-buy-a-swan-neck-chisel/ [1] 

Mine looks like this one.   Mine, a James Swan, sharpened to about 25
degrees, and definitely does not scrape, but pares. 

https://www.oldtools.co.uk/mortice-chisels/4716-clegg-swan-neck-lock-
mortice-chisel.html">https://www.oldtools.co.uk/mortice-chisels/4716-clegg-swan-
neck-lock-mortice-chisel.html


Mike in Woodland 

Links:
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[1] http://toolmonger.com/2007/12/10/get-bent-buy-a-swan-neck-chisel/