Before beginning any discussion of cutting meteorites it is always prudent to make mention of what rare things they are. Meteorites are among the rarest objects on the Earth. So some care and concern should be exercised when doing anything to them. I will not be around for more than a few decades at best, but if I do my job correctly the meteorites in my collection will be preserved for future study, knowledge, and enjoyment.
It has been thirty-nine years since I made my first cut with a diamond saw. In the years since I have cut thousands of slices of rock. Some very large and some now with meteorites very small. Each stone presents a set of decisions that must be made. Among these are how will I get the most material in the final form I want. What will be the best way to hold the stone in the saw for cutting. What is the best coolant and what thickness blade to use. I have written articles before on cutting meteorites. Often I attempted to answer every conceivable question I could think of. This time I think I will just hit the basics.
There is nothing more frustrating in this world than trying to hold a smooth round stone in the standard vise that comes with a rock saw. Especially if the stone is friable or has fractures in it. So several schemes have been devised to deal with this problem. One is to encase the stone in something else and give it a shape that can be held. I have never liked this it takes too long to prepare and you still end up generally making a first cut nearly blind. So modifying or in my case starting from scratch with a holding system was the answer. I have created a vise that resembles multiple C-clamps more than anything else. It allows me to hold almost any size stone and place pressure just about where ever I want. I works best for large stones of more than say a couple hundred grams but does work on smaller stones.
However, what really works best on small stones is to attach the stone with dop wax to an aluminum mandrel and place it in a holder I have constructed on the saw. This holder has a threaded advancing rod on one end that I can turn to push the mandrel out in the direction of the blade. After making a cut I simply release the locking thumb screw holding the mandrel tight and turn the advancing knob. I dial in the next cut by moving down a dial micrometerís plunger against the surface of the stone which is left after the last cut. If I know (and I do) the kerf the blade makes then I can easily calculate the desired push of the stone on the mandrel to get the thickness of slice I want. All cuts are perfectly parallel and all can be the same thickness if I wish. Since it only requires warming of the stone to get the dop wax to stick, the stone is not damaged and any residue of dop wax which remains after the cutting is easily removed with no ill effects to even the most precious meteorites. The one problem that can occur is that you are able to make cuts so thin that when the slice finally breaks free at the end it May slip down into the coolant tank. This can easily happen if the gap in the top of the saw for the blade is too wide. I have had to place pieces of brass shim stock against the blade on occasion to cover the gap so this cannot happen. I routinely make slices 1 Ĺ to 2 millimeters thick. I get many more slices per stone than I ever did with more conventional stone holding methods.
Of course if I am only cutting open a stone then I will still simply hold it and make the cut. I mention this word of caution. It used to be fun to show first time students of lapidary that the saw was perfectly safe by pressing your finger against the spinning blade. I can still do that (and did when I showed Paul how to make cuts) on the larger saws. But on the saw I use for all fine cutting the blade is so thin and turns at such high speed it can cut you. So hand holding should be done with care. You May not realize the saw has cut you with all the vibration and noise till you have been nicked pretty good. The same thing can happen when you are holding down a slice on the diamond laps for smoothing You can lose some flesh on your finger without even realizing that you have touched the lap itself.
I guess that I should mention that I only use one commercially available saw, All the rest of my equipment I have made myself. There was nothing on the market that I really liked very much. So I just put together machines to do what I wanted. I built a stepper motor drive that gave me stone advancement into the blade of anything from one step when I push a button to as fast as several inches of feed per minute. I mostly use the slow speeds of course. This brings up the next area of information for the beginner. How hard should you push the stone into the blade and thus how fast should you try to cut a stone. Diamond blades need to run at fairly specific speeds based mostly on their diameter and thickness. Since for all but perhaps the first cut on a large stone cuts will be done with a thin blade to minimize waste; I will just discuss how to cut using these blades. The manufacture of the blade will give a range of speeds that should be used. These are to be followed or the blade can be damaged. Too slow a speed and the blade will have insufficient stiffness to make a smooth straight cut and can be damaged by getting bent. Full thickness blades could be repaired in the past if this happened but there is no way to repair a thin fully edge coated faceterís blade. On the other hand too fast a speed will throw excessive amounts of coolant and make a very messy cutting experience. Also you will have to have a lot of drainage holes and a gap next to the blade for drainage of the coolant back into the tank. For small stones, shields and such to deflect the coolant and keep it off you and in the saw will obscure your view and inhibit your access to the stone.
So on to the answer. How fast to move the stone through the blade? I have learned to listen to the sound, but I guess the simple answer is slow but steady. Never force the cutting. Just keep it moving so that there is a constant sound of cutting that indicates no reduction in the RPMs of the blade. If the sound tells you that the blade is slowing or stalls completely you are pushing too hard. Conventional diamond saw blade are not particularly good for cutting metal. You will feel and hear when the blade hits large metal grains in a chondrite. The stone matrix will keep the blade dressed so that it cuts, but do not be surprised if progress slows for a few seconds. There is another thing here to mention. Donít go too slow. If you do not keep the stone moving forward at a continuous speed then when it stops it gives the blade time to do extra cutting with the bort on the side of the edge. This is where most of the deep streaks that are seen on a cut come from. If the stone is moved forward at a very smooth rate then there will be less deep marks to remove at the lap or sand paper.
There are two points in time during a cut that are very important. The first is the moment of first contact of the blade and the stone. You need to look at the stone and the angle of its surface that will touch the blade first. If it is sloping there is the distinct possibility that the blade will drift immediately at first touch. In that first few seconds of cutting the blade slides along the slope until the blades own strength forces it to stop bending. This effect will either result in a cut that wanders off of straight or May just result in a ground off spot on the edge of the slice where the blade slid before it bit into the stone. You usually can not remove this mark without removing an excessive amount of the slice. The best procedure to prevent this initial wandering of the blade at first contact is to go very slowly for the first eighth of an inch of cut depth and make sure that the blade has plenty of time to remove the rock without drifting along the outside of the stone. One can also confine the blade by again using some brass shim stock just below the stone so the blade can not bend at all. Done properly this will not at all reduce the speed or power of the blade but will control it for a perfect straight cut.
The second point in a cut where it is very import to pay attention is at the moment that the slice finally breaks off at the end of cutting. In the old days with thick slabbing blades and hard stone this was the point where a blade would dish. The burr for lack of a better word that is left when the slab breaks off could jump past the edge and the feeding weight could pull the rock with the burr in toward the arbor of the saw and deflect the blade outward. This would dish the blade. One learned to always be there at the moment of breaking off so that the vise and stone could be pulled back away from the blade immediately. This is not so much of a problem for thin blades since they are very flexible. What makes the end of the cut important is keeping the slices from falling off and becoming entangled in the blade. They can get cut, gouged, or broken while moving around loose. Again care is needed to stay away from the cutting surface with your fingers. But, I usually have a finger near where the slice will fall to slide it away from the blade after it breaks off.
One of the benefits of thoughtful clamping of the stone is that you can get several slices before you have to remove the stone to get another grasp. Every time that you reclamp the stone you have the possibility that it will not be in exactly the same relationship to the blade as it was before. This means a slice will be cut that will not be parallel. Or a sacrificial slice will be cut just to get going again. This make a slice that is undesirable for the collector and hard to sell in the first case, or one which is pure waste and counted in the overhead of cutting in the later case. This is another benefit I realize from the dop wax system of attaching the whole stone to the mandrel. I cut the entire stone in one set of slices always in the same orientation. Or I can cut what I want to now and leave the mandrel attached. Place another mandrelled stone in the saw and cut it. At any time in the future I can continue cutting the first stone or remove the mandrel and sell the remaining partial stone as is. All cuts are parallel and there is no extra waste from getting back to alignment with the blade.
Not too many months ago we had a large amount of material to cut and I began the process by spending some time just looking at the specimens. I determined how I would mount them and how I would make the cuts. I noted the rarity of the specimens and determined how many slices I wanted to produce from each stone. Some of the stones were small and there was only one piece. I wanted to make available the most slices possible. It would give us more sales and each sale would be at a more affordable price. On one of the stones I was able to make thirteen slices 2 millimeters thick. Each slice had a large surface to weight ratio and made this a bargain meteorite, at $25 per gram. The alternative would have been about five slices weighing much more each.
This brings us to a discussion of waste. The cutting process does eat up material. The thin blades produce a kerf a few thousandths of an inch wider than the thickness of the blade. The more cuts the more kerfs. But, compared to a full thickness slabbing blade we are still much better off with these thin diamond blades. I use 6 and 8 inch blades that are .006 inches thick. They produce kerf about 10-12 thousandths wide. A slabbing blade of 10 to whatever diameter can be from 25-40 thousandths or more thick. I wonít mention brand names here but I only use a quality blade that costs a few dollars more. They last longer and cost much less in the end. I have used these till there were holes worn in them behind the rim of diamond material. They were still cutting fine at even that worn out state.
The one problem that can occur is that the stone is too large to cut on the thin blade. In this situation I usually find myself making one cut on a larger saw with a thicker blade to produce two pieces that will be small enough to go to the thin blade.
After the slices are produced they must be smoothed and in many cases polished; or near polished. In the batch of cutting I mentioned a earlier I produced well over a hundred slices and end pieces. This means that I had including some edges and extra cuts where large slices were cut in half or even more, about three hundred surfaces to smooth. The diamond lapping machine I constructed, reduced this to a simple routine. Every piece went on the 180 grit disk on all cut surfaces. Then on to the 360 grit disk. Followed by the 600 grit where some would stop. Others would go on to the 1200 grit disk and the 1500 grit disk. Most of these later ones would also polish on a leather pad at high speed with a synthetic compound. In all I would guess that a thousand operations were required to make the hundred and fifty or so smooth surfaces. I lost not a single one to breakage in lapping though many were around 2 mm in thickness. In the end I had cut 25 stones of about seventeen different types of meteorites. Included in the batch were Carboneous, R, LLs, H-3, L-4, H-4 and many L-5 and L-6s. But my heart beat the fastest on some of the achondrite material I cut.
All my cutting and lapping is done with distilled water or alcohol. Great care needs to be taken to protect the meteorites from damaging chemicals. The slices are cut with a large amount of fresh silica gel on hand. The slices are plunged into the gel at every stage and remain there sealed until the next step. Each variety carefully kept separate and identified. Specimens are weighted before cutting and the slices are of course weighed after cutting for pricing. The loss can be calculated. Most of the time we do not do the loss figures because I have a good idea in my mind as to how the cutting went. But we have bought bargain meteorites in the past that were butchered by others. I have spent a lot of effort to redeem the most material possible. One specimen a number of years ago had been cut like a potato for home frys. The individual hand held it and removed slices here, there, and everywhere. The cuts intersecting and overlapping down in the interior of the stone. The stone once had a beautiful black super fresh fusion crust. But, it had mostly been peeled off by more than a dozen random cuts. Had this not been a real bargain when we obtained it, I think we would have passed it by. In the end there were several wedged slices and some oddly thick and blocky chunks. These resulted from all the original unplanned cutting. We produced a large number of beautiful slices after getting the meteorite back under control.
Planning is quite important in the way I cut. I almost never just grab the stone and shoot it through the saw. Some stones for that matter are never cut. I know they are a meteorite. I can guess pretty close what kind from their behavior. To cut them would detract from their physical form and destroy their beauty. Other are really made for only cutting. They are weathered and cracked and ugly. Sort of like myself. But they offer knowledge and opportunity for learning, and often are surprisingly attractive inside.
All meteorites deserve to have care used when being worked on, The material is not replaceable like opal or turquoise or something else from Earth.
Till next month. Jim