I'm trying to assemble the tools for scraping the saddle ways of a 1970s
Bridgeport series I vertical milling machine back from the typical
swayback wear pattern into flatness. One of the requisite tools is a
straightedge for testing flatness. I've seen the cast iron type made by
Challenge Machinery, which cost $100s even used. And I've followed
Michael Morgan's efforts to supply similar cast iron designs at various
stages of finish.

But I wonder, could not a granite surface plate be sliced up into
straightedges? I note that Starrett sells straightedges made of granite
instead of cast iron:

http://www.starrett.com/pages/437_straight_edges.cfm
(e.g., 2" x 4" x 24" black granite for $426)

Given that a new 12" x 18" B-grade import surface plate sells for about
$30, and could be sliced up into about 3 18-inch straightedges, ya gotta
wonder, eh? Machine some handles and epoxy them on?

As to the actual slicing, I have a wet diamond tile saw that I have used
on granite, so this is not a problem, and at $30/each for the slab one
could even afford to spoil a few tries. This diamond saw can cut
bevels, which has me thinking you could cut a custom tool shape to fit
inside dovetails. Or, granite kitchen countertops are the rage now, so
there must be shops nearby that could slice up a surface plate into
pieces. Or the local tombstone shop must have a cutting ability (isn't
that how granite surface plates were themselves invented, by a tombstone
maker during WWII when metal was scarce?).

Richard J Kinch
Palm Beach County, Florida USA
http://www.truetex.com/machinery.htm