>This, I think is "the rub".  The convex creates a "relief" on the back of the
blade which I think is >vital to scrape Babbitt to a smooth surface. The flat-
sided, sharp-arrised scrapers may in indeed >be scrapers, but they are not
_bearing_ scrapers. They will do general scraping such as >deburring, but aren't
going to make a fine surface on Babbitt. That's my uninformed opinion >and I'm
sticking to it! (But, see below, because open-minded John just found a
>counterexample.)
 
Scraping a bearing or a machined surface does not have the goal of making a
smooth surface. Gauge blocks are lapped to create a smooth surface but bearings
are scraped to create a surface that has a percentage of the area in contact. A
completely smooth bearing will wipe clean of lubricant and quickly gall to the
point of failure. Scraping leaves small pockets in the surface to allow trapped
lubricant to provide a film. The film separates the bearing surfaces so the
bearing actually rides on the film.
Having scraped many a press gib and managed a shop where hundreds of bearing
sections were scraped, assembled, and run in under load, if you make the surface
smooth the bearing will fail.
Machine tools have the beds and tables ground smooth and then scraped. The cross
hatch marking on the surface is the result of scraping. Scraping tools have
rounded cutting edges similar to that of a scrub plane blade. The marks left
have a radius that lets the edge of the mark blend into the surface without a
sharp edge.
Babbitt cuts relatively easily. It is softer than the surface it rides on so it
is sacrificial.  Scrapers for babbitt can be made from old files or various
other metals. In many ways Babbitt scrapers could be used for wood and wood
scrapers can be used for babbit. The materials are similar in hardness. The
purpose of scraping the two materials is entirely different.
Scrapers for steel gibs and machine ways and tables are usually made from tools
steel and sometimes from tungsten carbide to help maintain the edge longer.
Carbide has a tendency to chip so I’ve always favored tools steel.
If you are interested you can venture off charter and find out more about metal
scraping here: http:
//metalscraping.com/w2-Preview.html#01-Metal