grind flat surface on rocks / granite

[Richard Smith]

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

[Jim Wilkins]

"Richard Smith" wrote in message news:***@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
----------------------------------------
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

[Jim Wilkins]

"Jim Wilkins" wrote in message news:vcjmjv$13el0$***@dont-email.me...

"Richard Smith" wrote in message news:***@void.com...

Grinding flat surface on granite samples to make visually well
presented samples of geological features - eg. the "contact" between
different types of rock...

----------------------------------------
I bought some masonry cutoff disks to carve firebrick and if the rain stops
I could try one on the granite.

----------------------------------------
I did, it worked well. It's a black 7" SiC wheel, not diamond.

https://www.grainger.com/product/6A098?

jsw

[Jim Wilkins]

"Richard Smith" wrote in message news:***@void.com...
...

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

----------------------------
I've ground surfaces quite close to shape freehand with an angle grinder by
mounting them free to rotate and controlling the rotation speed vs grinding
rate by the position of the grinding disk. An example is the front
motorcycle tire for my sawmill which needed a wider crowned flat for the
bandsaw blade. The sawmill frame helped hold the grinder steady enough to
avoid high spots. I used the rear wheel as-is since the previous owner had
worn it to the cords burning rubber in the street, and the crown was
perfect. The blade was tracking centered after less than 15 minutes of
adjustment.

When grinding the end a straightedge shows if you are grinding concave or
convex. Touching the disk to both sides somewhat off the center of the work
makes it rotate slowly and guides the disk to cut pretty flat despite its
wear.

A variation is grinding the broken end of a drill bit or endmill square
freehand by rotating it against the wheel before adding the drill point
angle. I buy high quality dull or chipped endmills very cheaply second-hand
and regrind them for roughing, saving the new ones for finish cuts.

Holtzapffel mentioned a cup filled with hide glue or pitch as a chuck for
irregular objects, or actually high precision clock repair because the work
can be precisely centered as the melted glue hardens. This describes using
modern hot melt glue:
http://www.woodturned.co.uk/html/glue_chuck.html

For the metal sample grinder we placed the sample face down in a ring that
we filled with casting resin. The resulting disk fit the grinder holder.
jsw

[Bob La Londe]

Post by Richard Smith
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.

[Jim Wilkins]

"Bob La Londe" wrote in message news:vckkdk$17tla$***@dont-email.me...

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

--------------------------------

Search for "gem faceting machine".

[Snag]

Post by Bob La Londe
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
--------------------------------
Search for "gem faceting machine".

All this talk about flat rocks has pushed me right over the edge . I
just ordered a 9 x 12 x 2 surface plate ... supposed to be within a
tenth which is probably closer than anything I'll be doing . And just
over 60 bucks delivered .

[Jim Wilkins]

Post by Bob La Londe
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
--------------------------------
Search for "gem faceting machine".

All this talk about flat rocks has pushed me right over the edge . I
just ordered a 9 x 12 x 2 surface plate ... supposed to be within a
tenth which is probably closer than anything I'll be doing . And just
over 60 bucks delivered .
--
Snag
Voting for Kamabla after Biden
is like changing your shirt because
you shit your pants .
---------------------------------------------
Back when Enco had a store I bought a granite 12" x 18" surface plate from
them, and used it a little on the electro-optical projects from work that I
took home to design while machining. After retiring I haven't touched it,
the mill table is my adequately flat surface. I might make an oak stand to
use it as an end table.
jsw

[b***@www.zefox.net]

Post by Jim Wilkins
--------------------------------
Search for "gem faceting machine".

Probably everybody knows about Foundations of Mechanical Accuracy
by Wayne Moore. Just mentioning it for the record.... being the
first thing that came to mind after reading the thread subject.

bob prohaska