I’ve recently become enamored of a mineral called psilomelane. It’s
a beautiful black mineral, 5-6 hardness, with banded “ghostly” silver
layers. From my research, that name seems to be applied to several
mineral compounds with the commonality of manganese. The one i’m
working with is associated with the name ‘crown of silver’ and comes
from a mine in Mexico, i’m told.
My question/problem is this: i’m having difficulty cutting slabs of
this stone. On my small saw, I use a lortone 5" .018" core, sintered
rim blade. speeds: either 3650 rpm or 1800 rpm ( one to one ratio on
the pulleys makes about 3400 surface feet per minute on low). This
small saw cuts the psilomelane marginally faster than my larger saw.
My larger saw’s speed is infinitely variable, as i installed an ac
inverter drive on it. I have an unknown brand, notched rim 8" blade
on it. Any cut at all takes an infinite amount of time… something
like 1/8" in 30 minutes on a 1" x 1" rock. And, to get that I have to
use what i consider a possibly dangerous amount of pressure against
the blade.
I did put a new raytech (blazer- i think) blade on the small saw, to
no avail. I’m running both units with a water based coolant called
lube kool.
Once i get it cut, i can “get there” with no problem: grinding,
preforming, polishing, even faceting are easy enough. It’s that slab
or trim cut that’s a problem.
My saws are in good working order. I typically cut a lot of
turquoise, rutile quartz, sugulite, and the occasional agate with no
problem.
any suggestions?
steve in oklahoma
watching the humming birds flit and fly
My question/problem is this: i'm having difficulty cutting slabs
of this stone. On my small saw, I use a lortone 5" .018" core,
sintered rim blade. speeds: either 3650 rpm or 1800 rpm ( one to
one ratio on the pulleys makes about 3400 surface feet per minute
on low). This small saw cuts the psilomelane marginally faster than
my larger saw.
I don’t know exactly what to tell you about the technical problems
you are having but I do provide slabbing service & would be glad to
slab the material for you. I have and use daily a 20 inch Highland
saw for rock slabbing. We have cut psilomelane in the recent past
with none of the trouble you are describing. We use hydaulic oil for
coolant, & use continues rim blades.
My only suggestion Re: your used blades is that they may need
sharpening. Performed typically by cutting a slab of obsidian, or by
slabbing a small piece of silicon cardibe grinding wheel.
The metal (manganese) content in psilomelane may be causing you
blades to load up, we have had a similar issue as you describe when
cutting michigan cooper.
Re cutting psilomelane…this can be a problem, especially if it
is the old CA material that is more manganese than pyrolucite. This
is one of my favorite stones (if there is any favortism) and I have
cut a lot of them.
I do not recommend using a continuous rim blade. It does not deliver
enough coolent to the kerf which will quickly load up and ‘grab’ the
blade. Use a segmented blade to preclude this. I do not recommend a
thin blade…a .018 is a bit thin…try using a.020 or a.025 at
least. Again, this will preclude kerf build up and give a smoother
cut. By the way, do not expect to use water as a coolent with psi.
You need one of the special coolents such as KoolKut or Almag or some
similar thing.
If you are using a 5" blade you cannot cut a nodule much larger than
1" in thickness. The material is just too tough. Be sure the nodule
is held VERY firmly in a vise. The slightest movement will cause
binding. If you are hand holding the piece, back off periodically to
be sure you are not binding the blade.
One exception to above,…you might want to try the CBN ‘meteorite’
blade sold by Graves Lapidary Co (www.gravescompany.com) (I work
there). It is a 6"x.012" (in addition to other sizes) blade that is
especially constructed just to cut materials such as meteorites and
psilomelane, etc.
If you intend to cab the psi… be sure to use loooots of water and
cut very slowly. Otherwise it will load up you wheels. But…the
results are absolutely stunning.
Cheers and happy cutting from Don at The Charles Belle Studio in SOFL
where simple elegance IS fine jewelry! @coralnut2