Re: grind flat surface on rocks / granite

"Richard Smith"  wrote in message news:m134lug3zn.fsf@void.com...
Hello all
Thanks for all help.
Volunteering at local museum and hobby mines, benefitting from advice
on things here, and hopefully starting work again as a welder
imminently.
Grinding flat surface on granite samples to make visually well
presented samples of geological features - eg. the "contact" between
different types of rock...
Find is true a diamond-plate like for eg. sharpening plane-blades when
on-site produces a beautiful find shiny smooth grind on the rock
samples.
Problem - the removal rate is tiny - need a flat sample to start with
if going to do that.
Advice here is glide tools over the surface and go through finer and
finer grits getting a surface which is polished though not necessarily
machine-flat.  Comments
* this is the voice of experience
* is there really the need for the sample to be machine-flat?
Anyway, I was thinking how it might be possible to produce a flat
surface.
In the steelworks labs. there was the "swing-grinder" which had a
vertical spindle and you swung it back and forth over a sample in the
chuck, lowering it a bit per pass to produce a flat surface to start
going through the finer and finer emery grits with until you could
diamond-polish it to mirror finish.
I thought of base and column of a bench-drill, clamp a collar on the
pillar at height of finishing plane, and have angle-grinder on an arm
you swing back and forth.  Letting the grinder ride-up for light
"cuts", but eventually stopping at the plane dictated by the collar
locked to the pillar (column).
Anyone got a better idea / know how it should actually be done - if at
all?
Regards,
Rich S
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I tried flattening a granite protrusion in a walkway with cold chisels, with minimal success. Apparently granite requires a single point carbide tipped chisel. An angle grinder was somewhat more useful though I didn't have a SiC masonry disk for it.
https://www.cooksongold.com/blog/learn/how-to-polish-stones-by-hand-cut-gemstones-the-bench/
I bought some masonry cutoff disks to carve firebrick and if the rain stops I could try one on the granite.
Amazon offers relatively low cost versions of the standard jewelers' facet grinder. In college we used similar machines to polish steel samples for etching and studying the grain structure.
You could try a diamond wheel on a Dremel to reduce the high spots that coarse sanding reveals. When I do that on steel I sand in one direction and file or grind in another to show the difference. After borrowing the engine for the sawmill I found that its mounting plate on my second-hand log splitter was warped from welding and I hand fitted it to the engine crankcase. Pulling sandpaper through the contact area targeted the high spots for attack.
jsw