Sanding Guide

[Taogem]

Oct 25, 2007

I felt the urge to share portions from “Gemstones and Minerals”, A Guide for the Amateur Collector and Cutter by Paul Villiard. Credit for the following goes to the author and is not intended for promotional purposes or any financial gains. Only for the purpose of lapidary discussion and education.

While reading through the section about sanding, I found myself more than interested. I myself do still have problems with getting a sand and polish that I am completely happy with. So for anyone else lurking, reading and finding themselves in a similar situation in regards to understanding the best methods for getting the scratches out in a proper order via the correct papers prior to polishing, then this may be of help to you too
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Faster work can be done on the drums, when using belts covered with diamond powder. I have not switched from the silicon carbide to diamond yet, but it will be the very next paper I purchase.

The two talked about in this part of the book come in two grades. 220-mesh, and 15 micron . Then the silicon carbide come in a variety of grades, from 100 mesh to 600 for the final.
The author strongly recommends using diamond tools all the way through in gem cutting. The reason is that diamond abrasives cut smoother, faster, cleaner and last from 50 to 100 times as long as any other abrasive. The high initial cost is far out weighed by the life of the tool, and the ease and accuracy of cutting far exceed any other method.
The author suggests the two grades of diamond belts are all yo need to sand to the point where they can be polished. If you do not use diamond, then the silicon carbide grades of 220 and 400 for the second and on to the 600 for the final. It is recommended to have a machine for the belts with at least two drums. I have found this to be all so true as I struggle through the sanding process. So, this is my very next piece of equipment purchase. Another arbor unit so that I can have two additional belts readily available. I found one, and am picking it up soon. Be sure to try and use the expanding rubber drums for use with either the diamond or silicon carbide belts.

Ok, the stone is held against the belt with only enough pressure to cause the belt to cut. You will immediately feel the very slight pull of the belt when it is cutting. No more pressure should be applied, because the belt will not cut any faster. This was a big tip for myself ! This particularly applies to the diamond belts, since they cut so readily that much less pressure is required. At no time should the stone stop moving against the belt. Keep it rotating in a smooth, even curve, covering every point on the face of the stone. Over and over, touching each point, making sure you sand down along the edges as well s on the face. He goes on to say that it is the sanding of the stone that is the most important part of gem cutting. It may take an hour or even two to sand a stone to the point of polish, but unless every single scratch is removed from the gem, that scratch will stand out like the Grand Canyon the moment you put the final polish on it.
The 220 belt is used first, to remove all the scratches put in by the grinding wheel. While the stone is wet you cannot see the scratches. After you have sanded for a while, dry the stone and carefully examine it, preferably with a magnifying glass. You will readily see the scratches, and will be able to tell the difference between those caused by the grinding wheel and those caused by the belt. Continue to sand on the 220 until all the scratches on the surface of the stone are those made by the belt, and all the scratches on the stone made by the grinding wheel have been removed.
The book goes on to explain how to continue on considering the reader is working on a domed stone. 99% of my work is on flat cabs, so the process is different. With that in mind, I would like to concentrate on the methods and processes for starting and moving through the various grades of abrasives.
After sanding to completion on the 220, repeat the very same operation on the 400 mesh belt in silicon carbide, or the 15 micron in diamond. When you examine the stone under the glass after sanding on the 220, it will look even and smooth.
The moment you apply the stone to the next lower grit belt, the surface which looked even and smooth to you before will now be simply covered with what look like gouge marks. The scratches put on the 220 belt now appear enormous and deep by comparison with the scratches put in on the finer belt. You are now required to remove every scratch put in by the course belt, until the surface once more is covered with nothing buy the scratches of the finer belt. In the case of the diamond belts, the surface will now be extremely smooth and have what is called a “pre-polish” finish. It is ready to go to the polisher. In the case of silicon carbide belts, the surface will now be covered with much finer scratches than those obtained with the 220 mesh. When the surface is once again smooth and even, the stone is sanded on the 600 mesh belt, exactly as before. Exactly as before also, the stone will look gouged and dug up when you have applied it to the 600 belt for a time, and these old scratches must be taken off the surface to the last one. When the sanding is finished, the surface of the stone, when dry, should have a slightly gray look, evenly dull in appearance, with perhaps just the suggestion of a shine to it. It will have a very slight shine if done on the 15 micron diamond blt. All of your long and tedious labor has now been completed, and you have only a few steps more to go before you can hold a glowing gemstone in your hands and feel the wonderful thrill of having produced it yourself.

For myself, I am learning to watch the scratches very closely as I finish one abrasive and prepare to move on the the next. Like the author suggests, and I too have found it a necessity, and that is to use a magnifying glass. It really helps. The ones that come attached to a lamp are excellent for this work.

The next step is polishing the surface. Perhaps this will be something to add down the road, but for now the author has provided us with this great information regarding our sanding topic.

[Taogem]

Well the sanding process is getting much better for me. Pressing too hard on most papers was one thing I have noticed doing different now. Using each abrasive just to the point that it begins to drag the stone away from me. Like the post above suggests.

"the stone is held against the belt with only enough pressure to cause the belt to cut. You will immediately feel the very slight pull of the belt when it is cutting. No more pressure should be applied, because the belt will not cut any faster."

Using each abrasive starting with 100 or 220 silicon carbide and working my way down to the 600 silicon carbide in this way really makes a huge difference for myself.

I am finding that using this simple tip results in most all of my stones finding their way to the polishing pad with no scratches.

[Taogem]

Wanted to bump this to the top.

Never know who may be visiting as a guest for the first time, looking for information, and interested in learning some of the basics.

For myself, getting the feel of the sanding process was and still is key to successful cabbing.

The only thing I might add to the above posts is knowing when to consider to change out to new abrasives. I am still using silicon carbide. Have not made the important change over to diamond yet.

Seth has mentioned several times the importance of using diamond. My immediate realistic goal is to purchase something like one of the Gennie units. After working with Ralphs one day, it became apparent the importance of having that type of set up if a person is going to make this a long term hobby or business.

Don't get me wrong..... Just starting out, there is absolutely nothing at all wrong with the silicon carbide abrasives. I still continue to be able to turn out some nice cabs. It is the ease of the process that is increased when using a set up like one of the Genies that I look forward too enjoying on a daily basis.

So for now....., using silicon carbide abrasives can be a combination of using a new 100 grit belt as a 100 grit belt. Then finding ourselves using it in place of something like a 220 grit when it becomes somewhat worn. Same thing with a 220. I will use it as a 220 when new, and then find myself using it like I might a newer 400 or even a 600 grit belt as it becomes worn.

Agates are a big indicator for me as to when it is time to change into a new belt.

As the guide above explains.....  Always watching the progress of the removal of sanding scratches. After a short time it began to be second nature what to expect the surface of a stone to look like when finishing the 100 grit. Knowing that it was completely ready to move on to the next finer grit, and so on just prior to polishing.

Remembering all along not to use a lot of pressure. Letting each of the abrasives do their own thing.

The same is true if using silicon carbide or diamond. Maybe more so with diamond in regards to remembering to let the abrasive do the work. Diamond will only grind or polish in accordance to it's individual abrasive grit. Not pressure. Especially not pressure....

Any hooo...... just wanted to bring this topic to the forefront again. For me, getting a handle on the sanding process was the most important thing. Once I started to understand it, and actually get a feel for it, the processes become clearer and easier. The results were less aggravation and less time spent returning to previous grits two and three times .

Maybe others would like to add their experiences here as well, and or correct me on any of the above as I am in fact still very new and still learning...  

[freeform]

To me, silicon carbide is the only option when it comes to sanding cabochons in a biz sence. Even with the large production houses south of the border and overseas, tumbling cabs is the norm. And silicon carbide is the 1# choice. Silicon vers Diamond.

Here how i weight it out;

Life;
*i have and still use silicon belts that are over 4 years old
*The diamond i used to use, only lasted 2 years before they were shot.

In both cases, i would normally end up breaking the belt before i used the cutting action up.

Cost;
*silicon is much cheaper and can be bought from other companies that dont carter to lapidary, ie woodworking
*not cheap enough yet, but still coming down

The point here i feel is both will have benefit, and Tao points out, the sanding process in general is KEY to proper cabochon cutting. But you can achieve great results using both types of belts, silicon carbide, or Diamond. However, the real benefit i feel with diamond belt sanding is for soft stones. There is more control to the cutting action with well made Diamond belts. As the diamonds are applied in a single driection, and once worn in. Provide a nice cutting action. Silicon can be rough with stones, and is really ideal for harder stones like agate or jaspers. Silicon does ware in nice, but never as nice as Diamond. for the cost reasons and becasue i work mostly hard stones. I prefer silicon over diamond for sanding. But i do prefer Diamond for prepolishing and polishing. 

[Gia K]

I would like to know where I should start off with sanding and such. I just got a basic rock drill that has a shaft and diamond bits. I also got the entire grinding, sanding, but how do I polish after I am finished? Are there any books that I should get? Should I get a rock tumbler too? I'm a total novice when it comes to shaping, sanding and polishing.

Please help oh and I love this place!

[Taogem]

I would like to know where I should start off with sanding and such. I just got a basic rock drill that has a shaft and diamond bits. I also got the entire grinding, sanding, but how do I polish after I am finished? Are there any books that I should get? Should I get a rock tumbler too? I'm a total novice when it comes to shaping, sanding and polishing.

Please help oh and I love this place!

Hi Gia,

It sounds like you have a drill of some kind. Maybe a drill press?? That will be something that you will be using for drilling holes in your stones for the most part. Not for any kind of sanding or polishing..

When you say that you "have the entire grinding, sanding", not sure if that means you have some equipment, or if you mean that you have had some experience with the grinding and sanding so far....

There is some things you could read from the above posts that talk a bit about polishing.

Maybe if you have a couple of stones that you believe to have ready for polishing, and post a picture of them. If you can't post pictures, maybe tell us what type of mineral they are.

What was the final grit of sandpaper you were using when last sanding the stone? Do you feel as though any of the above posts about sanding sound familiar in any way?

Are you a novice? 

I think it is ok to say that from your questions, it is safe to say your just starting out.... You have found a great forum here with a lot of great people who are more than willing to give ya all the tips that your willing to listen too.

Glad your here!

[Taogem]

I wanted to add this post here from a post that Freeform posted in another thread. It fits here.....

If you are using a dremel type setup(hand held mutli drill tool). You will need to aqiure sanding bits in order to further work your piece/s.

Often we shape/carve with hard(metal) type bits. These often are around a 100grit, which is great for shaping. but you will need higher grit "soft" bits(200 and above) Ideally you should get rubberized bits, like these "Lasco sells Diamond bits"

notice they have them in 240, upto 1500 grit size. These, in secession, will sand your carvings. They will not polish them. In order to polish, using the same method, simply get "felt bits" In which you also get diamond polishing compound, load the compound to the felt bit, and use just like the others. Be warned you need each its own felt bits for each polishing stage you do. As with sanding, pre-polishing certain materials can benefit. For example, fire agates do well when pre-polished, i shape on 80grit, sand from 100,220,400,600 grit silicon carbide, pre-polish starting at 1200, then 14,000, and 50,000 diamond compound. And in some cases i do a final polish using Optical Cerium.

 however, Turquoise you can sand up till 600 grit, than polish using ZAM compound and be done. So it all depends on the material your cutting, and in time, you develope your own method of process when sanding and polishing. No matter the form or method used.  Hope this makes sence and is not too confusing. 

[seth]

I also use home made bits charged with diamond powder on bamboo and other materials in the finer grits. Put them in a seperate ziplock or container to stop contamination of your grit size. Always wash the stone after every grit change!!