Re: grind flat surface on rocks / granite

On 9/20/2024 12:48 AM, Richard Smith wrote:

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

Making flat surfaces from rubbing surfaces together IS a slow process. I can't imagine doing it.  The way I understand it is that it can be done to near laboratory or at least machine shop tolerances, but it takes three surfaces with swap of mates and orientation.  If I were to get into it I'd look at some of Robin Renzeti's (spelling?) videos on YouTube for the basic process.  He really goes down the rabbit hole on the subject I think.  There is also a dentist who got into precision grinding as a side business, but I don't recall his name or if he even has a YouTube channel.  Abom79 on YouTube (Adam Booth) worked with the guy on some stuff.  Might have just been making precision bench stones. I don't recall.  While they are not necessarily anywhere close to what you want to do, they may give you insight into how to do what you want.
That being said, the one thing you seem to catch my attention about was time and material removal rate.  I am always sensitive to time, and I don't know how you could improve that except by employing mechanical means to assist in at least the rough/coarse part of the process.  The problem I see with mechanizing the fine finish is you might need fairly fine mechanical bits.
--
Bob La Londe
CNC Molds N Stuff
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