I picked up a pair of Ice Bear flattening stones which are quite out of
Is it normal for flattening stones to come way out of flat?
Working on flattening the first one on plate glass and some 180 grit wet
dry paper. Not going so fast, might have to stop and pick up some 80 grit
wet/dry to speed this along.
One would expect you wouldn't need to flatten that which is supposed to
flatten the other stones straight from the factory!
Glass is harder than steel, but very brittle. One doesn't use steel to
cut glass, they have diamond glass cutters, or special tips to scratch
May have to make a trip to the lapidary supply house here in town and
get some flattening grit. I tried a belt sander 80 grit cubic zirconia
belt, but wetting it with the stone caused the edges to curl.
Glass is harder than some (most ?) steels, but I don't think it's
harder than all steels. I may be mistaken about that.
In any case, the glass is likely softer than the stone that the OP
is flattening and also softer than the lapping compound being used.
I'm guessing that the glass plate _is_ being worn.
the gemstone world uses a scale of hardness called Moh's. on Moh's
scale, glass and steel are both 5. silicon carbide, the stuff that
cheap sharpening stones and the grit of wet/dry sandpaper are made of
is 9 on Moh's scake. the roller wheels on glass cutters are made of
hard steel, pretty much the same stuff as files are made of. you can
also get them in carbide, but that's beside the point- the steel ones
a good hard glass like pyrex is harder than soft steel, but the steel
will still scratch it.
the action of a roller wheel glass cutter is kind of a special case in
the cutting tool universe. glass is an amorphous solid- sort of a
supercooled liquid- held together by surface tension. the steel wheel
has compressive strength greater than the surface tension of the
glass, so it crushes the surface of the glass even though it's not
significantly harder than the glass. the break in the surface of the
sheet of glass makes it easy to break cleanly along the line.
On Sun, 28 Nov 2004 13:53:37 -0700, email@example.com wrote:
... not to pick nits, but on the moh scale, a substance will not be
scratched by something that is softer than itself; it can only be scratched
by a material the same hardness, or harder. Thus, if the pyrex is
scratched by soft steel, it must be the same hardness or softer than the
steel. (IIRC, that was one of the identification methods for identifying
minerals). A softer substance may leave a mark, i.e. part of itself on a
harder material, one would have to remove the mark to determine that no
scratching had occurred.
On Sun, 28 Nov 2004 21:27:36 -0700, Mark & Juanita
this is the weakness of scratch tests. a substance that is stronger
will scratch a substance that is slightly harder, but weaker. soft
steel scratching hard glass is a perfect example.
now, steel and glass are both manmade materials, with a wide range of
specific composition and a wide range of properties, including
I'm curious about this, also. The explanations I've read about
lapping say that the lapping compound becomes imbedded in the softer
material and abrades the harder material. I'd expect that this isn't
an all or nothing proposition and that both surfaces would be abraded,
to a greater or lesser degree.
Any lapping I've done using glass has the glass covered with
(disposable) wet/dry abrasive paper, so I assume that I've not abraded
the glass at all.
I wonder if covering the glass with contact paper (or something
similar, but sturdier) would work, using lapping compound?
I do lapping and honing as part of my "real" job, so this is going accurate
in a real world sorta way, altho maybe not textbook....
...Honing is using an abrasive that is fixed in a matrix, usually just the
grit with glue...ie a stone.
...lapping uses a loose grit that gets embedded in a "soft" plate or
mandrel. "soft" means that it's softer than the steel or iron that you are
trying to sharpen or shape. almost all the time, there is some sort of lube
used...light oil, olive oil, kerosene, fuel oil or water being the most
common lubes. about the only exception to the soft vs. hard is when doing
cast iron...flattening the sole of a plane, for example...in that case, both
parts will be abraded, so watch VERY closely to make sure that you aren't
destroying one while trying to flatten the other...it is possible to get
both flat but you do have to be careful and pay attention.
As for using glass as a lapping plate, altho iron works better, glass is
easier to get, is much cheap and can be thrown out when bad things happen.
Glass is MUCH more brittle than iron, but it's surface hardness is actually
pretty soft and will allow the lapping grit to embed and do it's job. That
is, as long as you don't try to use a very course grit compound, so anything
courser than about 240 grit, use MDF for the plate.
Any question, feel free to Email me and I'll try to clear them up.
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