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Techniques for CollectorsTrimming Excess Matrix with angle-grinder

1st Jul 2015 17:32 UTCDana Morong

I had a big interesting ‘ugly’ specimen that for some years I had thought to get trimmed, but knew I couldn’t use a hammer on it as the interesting part would have shattered off. This is a 5 inch (about 12½ cm) chunk of basalt with a lot of tiny (1-5 mm) balls of analcite(?) scattered on it, that I’d once picked up loose at the rockfall at west end of Wasson Bluff near Parrsboro in Nova Scotia (this is well out of and far from the “protected fossil zone” as well as far from it geologically, so don’t come after me; I have read the actual rules and was quite within the rules and outside the area). It was such an interesting piece that I’d picked it up loose and had it sitting on a shelf collecting dust, and like a man in a barber shop, waiting for a trim.

I do not have a rock saw although I have nearly all materials for a small one. Years ago, an old friend, who used to pick the dump, fix stuff up, and give it away, gave me a small (about a foot long) table saw with a 6 inch blade, powered by a pulley. “You can make a rock saw out of it!” I had a motor with pulley I’d taken from a dumpster, but never got around to making it (only needs a carriage – to clamp and run specimens straight – a blade and possibly shaft adapter, and gumption to do it). However, a rock saw takes time to build, and then the blade is thin and one has to be careful not to bend it, and the cut would be only an inch and a half deep, and would likely be too thin for my purpose, which is simply to insert a wedge in the cut and crudely knock off a pound or two of excess matrix.

I had read, in various posts on internet (either RockNet on Bob’s Rock Shop, or on mindat.org) that one can use a tile or stone saw in an angle-grinder. Already having a cheap angle-grinder, and having bought at a yard sale a new blade (4 inch Quasar Turbo Rim diamond blade) which is about a tenth inch thick on its cutting edge, I thought that even if it can get only an inch deep groove, I could then put in a wedge and break off the remainder.

(I once used a Dremel tool with a tiny diamond blade to trim a micro specimen, when I thought that my clunky home-made trimmers – some of which have been very useful – wouldn’t work on that particular specimen; I remember that the diamond blade cut the basalt nicely!).

I got out the cheap angle-grinder. I had initial difficulty mounting the 4 inch blade because the middle of it, plus the adapter, was thinner than the axle where mounted, and would wobble (I think this was the fault of the cheap angle-grinder, made in China), so I used a large thin washer to keep it from wobbling, tightened it barely, centered it by sight, and then tightened it down (I had earlier conferred with someone about this). I also used a big head-face see-thru shield and leather gloves, and I try to stay out of the line of blade just in case something explodes (at 10k rpm a flying bit would have a tangential speed over 100 mph making quite a momentum, and I would prefer it be slowed by something else and not me).

I was doubtful as to where to cut this specimen so I thought I’d try a couple other specimens of the same matrix of basalt and see how it cuts and breaks.

The first was a chunk from Ross Creek Road quarry in Kings County, Nova Scotia, with an oddly positioned (at the time) 1 inch vug, with, on one side of the inside vug, analcime crystals and on the other inside lots of sharp natrolite (?) needles [these may be mesolite, possibly scolecite; I cannot distinguish them from natrolite. Under the microscope they now look like square cross-sections]. I used masking tape to cover the vug, to keep the dust out, also covered all that I wished to keep, to know where to cut when things get dusty (also keep the needles out of my fingers – I recall at the quarry using a home-made toilet-paper kit to wrap a specimen, but still got some in my thumb, and afterwards changed the whole kit and all, for a new one free from all needles).

The second lop-sided specimen was from McKay Head, just east of Parrsboro, Nova Scotia. This has a couple little vugs with the tiny quartz “flower” clusters within – not as good as some I’ve seen, but good for trimming – and what’s more, in nearby matrix, small angular inclusions of a greenish material of coarser texture, making an interesting specimen indeed (I’ll have to go back to the books to find out what that is). All these interesting parts I covered with tape to keep it clean and know where not to cut.

Face shield and leather gloves on, I set specimen in gravel of driveway and held down with toe of boot, and started up the grinder. It cut fast, blowing out a cloud of rock dust (I was sure glad that I’d taped over the good parts – also that the face shield kept most of the dust away from my face). Even though I can only get about an inch deep groove, going around it, is enough to later insert a wedge and split off the excess, just about where I wanted it. The needly-natrolite one broke a shallow cavity in the sawn back which is handy for a large label (it sits on the sawn side). The other one needed more than one cut, but now only one shows, and it is the bottom anyway, so doesn’t show in its sitting position. When I peeled off the tape I could see a crack, which if hammered would have gone right through the larger vug.

These two specimens are more aesthetic now, but they needed relabelling and I needed cleaning. I very carefully rinsed my prescription glasses of the fine dust to prevent scratching (I had just recently found an old can of pumice scouring powder and noted that basalt dust would be as scratching as pumice powder, being made of the same kind of rock. The 1-pound can of pumice powder had a written price of 17c on it, so must have been from my grandfather’s time). Then I relabeled the specimens.

Several years ago I had saved (from a dumpster) a big bag of double-sided tape, in pieces half an inch by three inches (actually a thin foam with very sticky glue). I peel off one plastic slip, stick it to paper, and trim off extra. Then when I want a sticky label, I write on the paper, peel off the other plastic slip, and stick it on. It sticks well to fresh rock. I have found that ball-point pen ink, in damp environment (such as a cellar), tends to come off in time (I’ve heard it runs when wet); I had one that had been damp, but was able to decipher the location from the few remaining letters, and then relabeled it with graphite pencil. Graphite pencil lasts much longer, so now I use that, pressing down hard when printing.

What about the big interesting ‘ugly’ specimen that inspired me to try this method recommended by others posting on internet? I think I will just leave it be, at least for a while, as it has the stuff all over it, except for bottom. After all, if there is any doubt about it, I can always trim it later, but I cannot add any trimmed stuff back onto it.

Later I remembered that I also had a specimen showing ore (from a completely different place and deposit), but its matrix was too big and wouldn’t sit right, and I’d always wanted to trim it. This one was harder because of more silica, but it cut fine. This time I also wore (besides the mentioned safety wear) a cheap disposable dust mask, that goes over both nose and mouth, just in case of heavy metal dust (I plan to use dust mask each time from now on, even with specimens as innocuous as the first two). Then (after relabeling), I cleaned up, took a shower, changed to clean clothes. These few formerly-lopsided specimens look a lot better now.

It then occurred to me that even though ordinary lapidary blades are said to be not particularly hazardous, due to their abrasive and slow action, and (usually) smooth edges, that this blade, having a sort of fluted edge, and cutting through rock at such a speed, could be hazardous to boots and what lies within (whether steel-toed or not, much too close for safety). Therefore I built a clamp or vise, from 2 foot-long 2x4s (wooden), 4 foot-long threaded rods (steel), and lots of nuts and washers, connected with L-angle steel to a board, on which is part of a steel box to protect boots which help hold down the whole thing. Then I realized that the board might be better if could be moved, so the L and other attachments can be clamped with C-clamps – and not even a boot is needed to hold down the clamp, but something heavy, or it could be fastened to something. Anything to do the job and hold it while keeping it away from boots. Precaution is better than injury, and safety is better learned presently than too late.

One last bit: I had another, though not large, but oddly shaped specimen (of the same basalt as before), and taped over the vug I wanted to save (I don’t trim all of them; I have a bigger one with more matrix but as it is proportioned right I just labeled it). Then I set up the clamp, and found that a few minor modifications would be useful. I didn’t even have to use a boot to steady the clamp; it had enough stuff on it and its pieces dug into the gravel (I still used the metal box over the nearest boot). Then I got all safety gear on and ground away. Afterwards I relabeled the specimen, and then added some nuts and washers to the inside of the clamp, to be used only when needed, in addition to the ones already on the outside (yes, I had to undo some stuff to get them there). The clamp, being made of wood, grabs well, and the whole thing requires some time and patience, but this is well worth it, especially considering what one gets from it: Less hazard of injury, and a nicely trimmed specimen as well. It makes it all worth it.

2nd Jul 2015 21:43 UTCJohn Oostenryk

Hi Dana,

Congrats on success! Successful trimming is a joy:) It is always fun winning the "too much matrix" battle.

I also applaud the re-purposing of stuff- there is certainly satisfaction in better home built for less!

A few notes to add to your excellent thread- gleaned from a number of years of utilizing an angle grinder with diamond blades and dry cutting.

Thought I would add a few details for reader's further consideration.

A) I use a chain vise to hold the grinder body. Plug the grinder into a (power strip) next to vise to use strip switch for ON/OFF.

That way the tool is immobile- and you can do carving and angles too, by bringing the specimen to the tool. Escapes issues with maybe damaging side stuff with boot pressure;)-

Don't tighten chain vise too far or risk binding the electric motor in the plastic bodied grinders. Snug is good- you will surely notice if grinder body is shifting/twisting when cutting, indicating too loose. That is fair bit before it would fall out!

I would mention my current setup is a Rigid brand pipe stand with integral chain vise but I started out with a very second hand, bolt on chain vise, lagged to a large log stood on end (cut smooth for the purpose.) The bolt on ones can be screwed to a picnic bench corner, truck tailgate, etc ;)-

B) Get a rubber 1/2 mask with low profile (thin)filter cartridge (they are soft even -not rigid). $11 for 3M mask and $8 for pair of filters. I LOVE mine and have had for years.

I wear glasses with mine and they don't fog.

They are FAR more effficient and comfortable than those nose pinching, stuffy disposables. I despise those paper ones! :)

I reverse blow off the filters and wash the mask in the sink.

You can also get the different chemical cartridges for same mask, for painting or for HCl if doing min prep that way...

C) About the diamond wheels- continuous rim sets up less vibration- nicer to your fragile minerals or crumbly matrix. Segmented rim is faster cut/cooler on harder stuff, but it does suck bad when the piece vibrates apart in your hands!

Make sure your blade is rated for the speed of your grinder-- Hi speed 4" / 4.5" wheels ~ 11000 rpm.

7" -8" wheels are maybe 7000-8000 rpm(and will fit on a 4.5" grinder-Bad Idea!) I will skip the gory story -seen it!~

D) Yes- as you say, cover the fragile stuff!

I have used duct tape, where piece is clean so it sticks effectively. But it has issues in colder weather and may release leaving gaps for the dust.

Certainly remove a.s.a.p. so you don't get glue stickiness on specimen (especially in hot weather.)

If the material in vug is water tolerant and especially if matrix is dirty... Before a "first and only time cleaning"? I have been using soft toilet paper thoroughly wet, and blobbed into the opening. You can vary the wetness to make paper pliable/moldable- doesn't need to be dripping.

This also works to dampen vibrations when working. Less 'whip lash' to cleavable xtl tips under concussion.

I must say the wet TP method is much faster processing too!

Works in the rain(tape won't), no residue if ya leave it for a while. If it drys, it will be a bit rigid so DO re-wet to remove--wouldn't want to pull something from edge with it.
I like it a lot!

E) If covering vug--Study carefully (and mark cut in pencil-cleans right off after) TRUST me! Because you can't see the mineral as visual reference to slight angle variation in your cut... Sometimes I 'wing it' but Mark once =>cut successfully!

That is my 2 cents! Happy Hunting y'all!

~JO:)

3rd Jul 2015 00:43 UTCGary Moldovany

I like this thread a lot! I bought a Ryobi cordless angle grinder a few months ago and I am very pleased with it. I bought some cheap diamond blades on Ebay(with the fluted edges) and it cuts rock like a hot knife through butter. The batteries don't last that long, so I got a few extra ones. It sure beats the hammer and chisel and you don't get the shock waves that shatter off good crystals. I also recently purchased a really great old mineral trimmer, the clamp & chisel type. I discovered that odd shaped rocks will split much better if you cut a small groove where you want it to break. The only drawback to using the angle grinder is the spray of dust all over everything. I can see where a dust mask would be good for this.

3rd Jul 2015 22:49 UTCDana Morong

Great comments, lots of good points, from both.

As to comment A) (of JO) I personally prefer to hold the machine and keep the blade pointing another way. Bringing the specimen to the blade reminds me of using a table saw (in which operators sometimes end up like 9-fingered Frodo). A neighbor told me that he doesn't like a table saw, with the blade cutting toward him, he prefers another way. Then I noticed a couple of his fingers are shortened so I didn't say anything more about the subject.

I will always remember old Mr. Foley of shop class, whose stock saying was "I don't want to have to send one of you kids home with your fingers in a paper bag" (why paper and not plastic I don't know). Another fellow, who at one time collected minerals (he shared some pocket collecting with me, let me keep what I found), said that he was similarly impressed by Mr. Foley's unforgettable saying, and that it was probably at least partly responsible for his still having all his digits.

Yes, that dust does get all over. Which is why I have to change clothes and take a shower afterwards, it really gets into the hair. A face-mask (as well as a dust mask) is good, but mine doesn't cover the top of the head. But even if it did, some gets in anyhow and I have to rinse the fine dust very carefully off the prescription glasses so it won't scratch them (they are polycarbonate not glass!).

20th Dec 2015 04:12 UTCJohn Oostenryk

I meant to add this way back- just read reference back to here via Jonelle's revisit to a similar thread...

Anyhoo- RE: cutting off body parts! Worry not, this is an upbeat post, nothing gross! :)

My, to date, experience with end results, offered for your consideration~

I have used many different 4" diamond blades intended for angle grinders(high speed) and 7" tile saw. I have an 8" tile blade too. Also have run a welll used 12" Partner in past, and now have a 14" Stihl 420, gasoline powered (portable!) "concrete" saw.

I would make a conservative guess of several thousand cuts to extract and/or later trim down hundreds of pieces. At present, 99% have been sedimentary matrix. They work great in limestone and dolostone. It is VERY surprising the differential hardness in cutting these 'soft' materials. Add siliceous content and it steps up a couple notches. I have had a couple chunks of high calcium limestone that refused cutting from several blades. (not all are the same, and a used blade may be lacking diamond when needed, as in this example) This is maybe a topic for elsewhere, but note that quirk!

Crystals all have cleavage issues that magnify with solid matrix. You just can't hammer too much off without risking killing the crystal you looked so hard to find!

So carry out the rock and cut 'er down at home!

This is easier when vehicle access gets you "close" to locale- like in permitted quarry~ (carrying bigger.)

In past, I unhappily killed nice things trying to cob down for portability... At least it was always a learning situation.

I do prefer to carry out, but if not possible, I use the larger gas saw on location, to remove an oversize chunk, which is portable. Positioning is always awkward in field- so I don't attempt a finished piece there. Bring it home to sure footing, where you can take all the time needed to ponder (and draw!) exact angles needed to position your prize nicely once finished:)

As I have used 4" the most to date, it takes multiple cuts to get a finished piece out of a large matrix. Cut, turn, cut, turn, cut, stop. Then use thin wedge to pop off both sides and a bottom. Then maybe repeat all again, because the piece has 10" or 12" inches of extra matrix... The 4" blade only cuts 2" or 2.75" (think half that, plus subtract shaft diameter for realistic cut depth with a blade.)

So about those slicing and dicing-- having pointed out I have a fairrr bit of time (experience) playing with these things. (Your mileage may vary...)

Last disclaimer first- I can NOT speak about GEM blades. I hear those super thin ones are Very Sharp- THAT makes sense to me. I would not touch one to see! Ask a long time user ;0 Or try a piece of leather?

OK- back to typical diamond, general purpose dry cutting and wet tile blades, with typical thickness.

These will not slice skin.

Try it! They do not. (cautiously) Rub your finger tip over edge of (non running) blade. No slice.

I DO do this when teaching people in person, to get them past the natural fear of laceration. That scared hesitation most bring to this operation must be overcome and educated into respect. Fear brings no joy to operation of any equipment.

It certainly is conducive to possible injuries due to jerkiness or hesitation. I think you understand what I mean here.

So I show reality with a touch to the blade.

I do show the same with a moving blade. I will lightly touch it, just to show it does not cut me. I always feel bad, a tiny bit, as I can see they have a true anxiety about this, and I do not mean to contribute, but it is very worth it, when they see the result is nothing. (It feels like a sandpaper rub-a discomfort I am fine to bear to dispel another's fear.) OF COURSE- I Repeat to them- YOU will not be touching that, just the rock does!

If you tap or touch them with finger tip- no laceration. Leaving a finger on it will abrade in short order of course, but will not cut you like (just glancing at) a WOOD cutting blade. Saw blade for wood- EGAD- scary sharp, slice through soft stuff like proverbial hot knife in butter!

Diamond blade- Nope!

What diamond blade WILL go through rapidly is hard material. Fingernails are bit harder than skin, and will be removed rather quicker than that skin sanding action.

That is NOT pleasant. Yes, I've done it twice in past, working on awkward shaped, heavy piece- somewhere in process lost track of finger tip placement and top of fingernail contacted blade edge. Once through my glove, once with no glove...

Now, to be clear- what happens is you will gradually-but VERY rapidly become aware of a burning sensation. Like having a flame applied. That is the heat of friction as it wears into the nail. Sharply unpleasant, and happens faster than blade will go through the nail (at least my experience~ maybe I am slow cutting? Not a bad thing!)

You will have a groove in top or edge of nail. The heat dissipates in a second or two, and it will smart a bit afterward like any 'injury' to self (blister/bruise/cut etc).

I believe, thinking about the couple times, it was with a 4" blade. The bigger specimen was somewhat obscuring the smaller blade once cut commenced. I use bigger blades most often these days, and thus part of blade is usually visible more during each cut. LIKELY too- I am ever MORE careful too-LoL!

If you ever watch a jeweler/lapidarist cutting thin material slabs/cabochons on a "trim" saw. They have their finger tips adjacent to each edge, securing both bits that are cutting from flying away once separated. Focus and precision are key! Note they don't have long nails either. Now you know why! ;)-

Summation- Be Careful, NEVER hurry. As always around power tools, respect electricity and inertia!

Respect that diamond blade, but confidence more/worry less, as you would with a razor blade or wood cutting blade.

20th Dec 2015 06:15 UTCJohn Oostenryk

Some other details~ Offered for consideration of peers, new and old:)

I have my preferred way of running at present- based on machinery I have ended up with. I DO probably sound "set in my ways!"

Years of experience, blah, blah, blah...

Noooo! :)

Working with materials, you stay fluid. Repeatability is very favored! Nothing is perfect, but you strive for better, and random shtuff keeps you on your toes. Avoid complacency ;)-

I write about what works for me mostly, (because something else(elses-plural?ha) didn't go as well for various reasons- unmentioned, due to time and writing patience, likely:)

Funny to me- cutting specimens is the only time I prefer to 'tie down' angle grinder. Years of using angle grinders (4"-9" unit) in mech trades- I run the grinder against secured 'workpiece' (think metal machinery fabrication, welding, paint prep, etc)

I prefer to bring rock to the secured cutter for five? reasons. All equally important really.

The only time I do not- is when rock is just too big to lift to cutter. Weight secures rock to ground--I then cut away excess till I get to smaller portion I can comfortably maneuver.

1) The grinder is a "regular" shape- which can be firmly/confidently secured. Best, that hold down is repeatable every time. Every rock is different; shapes, crumble factor etc, do not lead to easily secured object.

2) I turn angle grinder head, so that blade (now vertical) rotation is turning toward me/ground. That means dust(dry) is being directed down and away from me.#1@end

ALSO- any possible bind of blade vs rock during cut, will:

a) Push piece/hands away from tool or

b) If pulled from hands, it will fall/fling down. It may bonk your knee or toe etc, but wear pants and boots! FAR better than torso/face

c) If bind on stone and you hold on, it will jerk to stop on 'back side' of bottom of grinder. C is unpleasant wrench possibly, but is a stop, no flinging away.

3) With the grinder secured, I have less cut roughness(called Chatter). Note-These blades are not going to give a glassy smooth cut- whichever you hold or secure.

With the MK brand tile saw(water cooled) I use, I am regularly surprised by the smoothness of cut face. This is due to both the rigid mount blade and the sliding base to feed (by hand) the rock through. #2)

4) The thing I don't like about hand held grinder- is in cutting- there is chance to bind the blade. Inertia means something has to give. That translates to something getting 'jerked'. I have found over (almost 40) years of regular tool use, the human can't totally control the tool in that case. The tool is stronger(even 4"). tool grip size and personal strength is factor, but I hate that painful wrench the wrist etc get. I find it more often in held tool than when holding specimen.

5) I started out saying "I have 2 reasons,(now edited) to 5."

This last is important. Because I'm holding specimen (no longer just a rock.) I have control of the (to me), more important end result. I have had pieces separate unexpectedly from unseen fractures.

I use super glue at times to avoid splitting with SEEN fractures. Lots of success but sometimes not~

I hate to say dropping the good side would not end well for crystals.

Complex to ensure against this by securing specimen as opposed to tool and time eater doing.

Also- I have cut into (unknown) good vug when removing wanted part. Good to be holding both sides at end of cut. Drop off would have been bummer for surprise revealed.

6) I said 5? I thought of one last difference in using a vise for specimen. Has to do with being able to "hold" complex/fragile specimen with your hands without damage, where trying to tie down~ just can't get it safely. Trying to cut at tied down piece has obstruction issues too avoiding tie down?

#1@end Important!! DO DO DO wear glasses, goggles, or best to me, a FACE shield. ( I have prescription safety glasses and I wear shield over them.

(clear plastic, tilts up from headpiece,like used in grinding post welding(not weld shield!)

BECAUSE--blade rotation either direction will toss crumbs at you. Don't risk an eye imbed. Corneal wound is sad.

I forgot to mention- in position, I remove the grinder blade shield . It hangs up on specimen, reduces cut depth- so I remove it.

YOU Do at YOUR discretion. NOt because I said so... I didn't! ;)

Whether in place or not, wear a face shield. Goggles tend to fog, face shield does not.

2) A moment about tile saw. I borrow time on a friend's 7" unit, I supplied the blade (the cheap end- lucky me!). Love using it as not annoying dusty and less specimen issue by avoiding electrostatic dust factor. Can use indoor in winter when COLD outside;)-

However- it cuts a thin tile fast. BUT- It is only good for a couple inch cut in sedimentary materials at slow feed rate.

It is only good for about 2cm max in harder stuff- like agate/thunder egg. 2cm is thicker than any tile I suspect!

Within design parameters- it is slick, but Shape variation in specimen rough is problematic rule, thus utility is quite limited on rough specimen trim duties.

LAST-- I know fellow enthusiasts, who have cemented(literally) or glued onto, too, to have graspable shape of specimen for cutting. Of course you cut away that 'secured' section of poo~ and you have your freed cool piece!

Options...

Nuff thinking about variables and generalities for now :)

Best regards,

~JO:)

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