An Article In Meteorite Times Magazine
by Jim Tobin

Meteorite Cutting

Since I continue to receive a good supply of emails about cutting meteorites, I thought maybe it was time to revisit that topic once again. Though to be honest there are several discussions in the back issues of Meteorite Times already.

I have talked about planning the cutting of the specimen before touching it to a saw blade in the past. I feel that it is important to think about the cutting in order to get the most slices with least waste, or the best cleaned up meteorite from a broken stone when only one cut is to be made. More about planning can be read in the back issues.

If a stone is going to be cut like a loaf of bread into as many slices as it is possible then some special consideration is necessary. In the best world you would only set up the stone once in the vise or holder and then just move it laterally into the blade in equal thin movements. In this best situation that would make all slices parallel. In the real world you have to reclamp the stone to get another bite and move out more material to cut. Things can get very unparallel and a clean up slice may have to be made. This will be waste generally since most collectors justifiably hate unparallel wedged slices. I wish I had a good general answer to this problem but the fact of the matter is you just have to try and reclamp the stone as parallel to the last cut as possible. Sometimes you can cut a wedged slice into several smaller slices and using a diamond lap bring each of the smaller pieces into parallel again. There is some wasted of course but the pieces gotten are fine.

On a small stone, say up to about 300 grams it is possible to apply a mandrel to it with dop wax and that is what I often do. I have dial micrometers on my saw that let me move over the last cut surface an exact amount each time to get uniform slices. It works better than guessing by eye the amount of shift and the kerf of the blade. A threaded plunger with a knurled wheel is turned to push the mandrel out sideways across the blade. The micrometer is on a swing pivot so that it moves out of the way during cutting and stays dry.

There has been a recent internet discussion about coolant for cutting. I never use straight alcohol. It is very flammable and the vapors are harmful. Prolonged contact to skin is also hazardous. I use distilled or purified water. The important thing is that it be chlorine and chemical free. Water does not provide the lubrication and cooling properties that the diamond blade requires for good life. So blades do not last as long as they could with oil. But our goal is to make beautiful meteorites not agate slices. So keeping the meteorite fresh, clean and naturally colored are way more important compared to blade life.

I have build a stepper motor feed for my saw that is infinitely speed controllable. The motor drives a threaded rod the moves the stone holder back and forth passed the blade. But I will often use the manual feed wheel to turn the threaded shaft instead of the drive motor. I like to get in there and do the cutting by sound. If something bad should happen like the stone fall apart on a crack I have control of the forward motion and the cutting. It takes a couple seconds to throw the power feed into high reverse. In that short time a very thin blade can be dished.

When cutting a larger stone in half with a full thickness blade it is not uncommon for it to break near the end of the cut. You need to be holding both halves of the stone. Lightly hold the piece being cut off so you can quickly remove it from the blade area. Hold more firmly the stone in the vise so you can pull the clamped half back out of the blade (if you don't have power feed). You should be watching the cut so you know that you are almost through the stone. Be ready for the stone to break.

2800 gram half of Sahara 99676 showing end of cut break off along bottom of photo

Larger stones have always posed a problem for clamping in the stone vise of a rock saw. I am working on a new design of stone vise that I have hopes will be the final version for me. All I can say at this point is to do the best you can and get as many slices as you can before you have to reclamp the rock. On many occasions I will make two or three cuts through the stone creating thick slices that I can then turn on their side and run back through the saw for the final size slices. For really large stones I have to forget the one saw completely and use a bigger rock saw with the full thickness blade of .050 inch. That is too much waste for doing very many slices. So the previous procedure of just reducing the stone to very thick chunks is what I use the large saw for. It likewise is designed to be used with cutting oil. Since I almost exclusively cut meteorites now it gets filled with water and then drained after cutting. Most full thickness blades have a steel core that will rust quickly if left in water. Many of the thin blades with continuous rims of diamond have stainless cores, but the bonding plating for the diamonds is still not really rust resistant. I drain that saw of coolant also after use.

1 kilogram chunk of NWA775 ready to be run through a smaller saw to make finished size slices

From the descriptions given it should be clear that my smaller saw was designed and built from scratch by me. It needs a little work after 10 or 12 years of heavy use. But, it still runs pretty nice. One thing that you just have to get used to if you are going to do a lot of cutting is getting wet. To really be in control and watching the cuts like you should, you will probably find that the plastic shields are in the way and a bother to have on the saw. For all the finish cuts where you are taking complete slices and making partial slices you will not be clamping anything just hand feeding them through the blade. Getting wet is part of the process. I wear a clear plastic apron and a face shield. I try to stand to the side a little to get out of the direct spray off the cut, but soon I will be wet regardless. I keep some old towels near the saw to dry the majority of the water off before putting the slices into cans of fresh silica gel. Towels are good for drying hands too of course. One obvious word of caution; water and electricity have never mixed safely. Always keep in mind where your motor is and how the flood water on the top of the saw is draining back down into the blade tank. Don’t touch any wires or let wires get wet. My saw is made almost entirely of ¼ inch Plexiglas with just the motor mounting, rock clamp, drive mechanism and blade shield being of metal. Most commercial machines will be metal and electrically conductive. Keep it as dry as possible. Don’t let the floor get wet where you stand. Use ground fault protection on the power outlet. If you are like me you will be working alone. Protect yourself since no one will be near enough to help you in an accident.

Most anyone that does much cutting will find themselves with a meteorite that they want to make into truly thin slices. I am now talking about slices in the 1 millimeter thickness range. This is where my micrometers and engraved mandrels are really handy. But, there is a problem that often occurs when the slices get really thin. They slip down into the coolant tank after they finish cutting, Yes, you can try to hold onto the slice, but there is often little space for that. And if the blade cover is up you are really getting soaked. These really thin slices fall down through the blade cutout in the top of the saw. And they are pulled down fast by the rotation of the blade. I have found the easiest solution to losing thin slices into the coolant tank is to place a sheet of shim brass along the side of the blade, covering the gap that the slice could fall through. The slice now falls on the shim brass. I just clamp the shim stock next to the blade with tiny c clamps or the spring clamps that hold stuff while glue dries in woodworking. Anything will work just so that the blade is not actually touched, but the slot is covered. The slice can no longer go down into the coolant tank. Taking the top off a saw to recover slices is just a big time waster to me. Of course none of this is necessary with normal thickness slices that just fall to the side of the blade.

I have often told people to listen to the saw while cutting. I guess maybe that is something I learned as a kid on the big saw I used exclusively back then. If it was too loud you were pushing too hard. If it produced a grinding whine then it was feeding at the right rate. Since that saw used heavy lead weights to help pull the big stones forward it was a balancing act between letting the weight run wild and jam the blade or restrain it and listen to the sound of the saw. Now I use the same technique with the super thin blades to regulate the cutting speed. I try always to keep the sound at a constant volume. The smoothness of the surface will be much better if the cut is done at a uniform feed. One problem is that diamond blades do not care for metal much. They naturally slow down and clog a little on metal. So when cutting chondrites with large metal grains or veins there is a tendency to stall at the metal. Continuous rim blades so popular now for meteorite cutting can make very nice surfaces if fed even and straight. However, being as thin as they are it is possible to get a curved cut if you are not careful when hand holding a stone. You may get part way through the cut and the blade will finally pinch up and stop. Try limiting hand holding to just finishing cuts when making partial slices from larger slices. You will get better results, longer blade life and less waste if the stone is held firmly during cutting. And I realize it is a pain to mount the stone for one cut.

There are some very thin versions of the oldest style diamond blades available also. This is a blade that instead of having diamond plated on the core or sintered into it; has the diamond powder forced into grooves and the metal press down over the diamond powder. These blades unlike continuous rim blades can be “sharpened” when cutting slows down. By running the blade through a dressing stone new diamond is exposed by removing a little of the rolled down metal. It is mostly a matter of preference which blade you choose. I currently use continuous rim blades. They are very aggressive cutter but have a relatively short life of a couple hundred cuts I would guess for me. That is depending on how many cuts I do actually dry on very special material. The very thin “notched” blades might last longer but have steel cores and will rust very fast if the saw is not drained and blade spun dry. On the same topic of blade types for cutting meteorites. I found the CBN (cubic boron nitride) blades that are supposed to work for metal rich and iron meteorites not to work very well for me. It may just be that I expect them to operate just like diamond blades. I may not know how to get the most from them. But, I found cutting to be way too slow for me even on low metal stone meteorites. And their cost was high than diamond blades.

In any discussion of cutting meteorites there is the how to treat them after cutting discussion too. I don’t put them into the oven after cutting. Since I cut with only distilled or purified water I am not too worried about chemical corrosion. There is only the danger of normal rusting from the air, water, and iron triangle of meteorite death. So I will usually hand dry the slice or individual after cutting to get as much water off as possible. Then submerge the meteorite into silica gel. The drying off is to keep the gel from getting depleted quite as fast. After I am done cutting the batch of rocks I gather up all the pieces out of the silica gel containers and lap them smooth. Some will be lapped to 220. If that shows them off best. Others will be ground to 600 or some may be polished. It all depends on what will make the meteorite most attractive. When they are finished with grinding or polishing I put them into 99.9% isopropyl alcohol and give them a good rub down and toothbrushing to clean off any fine grinding residue or polishing compound. If they are to be sold they are vacuum packed in labeled bags until its time to be photographed. If they are collection pieces then they are either displayed or stored in dry boxes.

I have never had to really do the soak in alcohol step. Unless of course they have a problem prior to cutting and need treatment first. I do use alcohol as the drip in the lap. There has never been an instance of a spark on the lap and I have not worried about ignition with my homemade equipment. I can not tell you that you can use alcohol as the drip with your lapping machine. Your machine might produce a spark and be dangerous. But it is very possible that all that exposure to alcohol during lapping is one reason that I need no soak in alcohol later.

This may not be the last offering of information on cutting. I realize some of this has been repeat but hopefully enough was new to keep the regular reader interested. For the new reader this is hopefully a good introduction into rock cutting. Topics like blade speed should always be considered based on the manufacturer’s specifications. Thin diamond blade can cut you which used to not be true of full thickness rock saw blades of the past. Segmented diamond blades can also injury you. Use all normal workshop safety habits like eye, ear, and when needed dust protection. Avoid contact as much as possible with chemicals. And enjoy the great hobby of lapidary work with meteorites.

1800 gram half of JaH 055 mass that is ready for further cutting