Saturday, October 16, 2010

How To Make Cabochons

There are a lot of places on the net which show how they make a cabochon, and  lot of them are helpful, just seeing someone else do it can help a person a lot. I am going to attempt to show you how I get my angles, in the beginning stage, the grinding wheel. This will be considered by a lot of cab makers as a "wrong" way to do it, but I dont think there is a wrong way. I believe you should use, and do, whatever works best for you, do whatever it takes to get the result you want in the end. This is just what "I" do.
The grinding wheel: I use a 100 grit SIC grinding wheel, not diamond, but either works just as well.
First, choose the side of your pre-form that will be the "face" of the cab, or the side you want to dome. In this photo you see me holding the cab face up, and pointing at the top edge of the stone. This is the edge we will begin getting our dome with. Always focus on this edge, alll the way around the stone for the first phase.

Here I have taken that stone to the grinding wheel, the stone's FACE edge, that edge in the previous picture, is against the wheel. I move mine up and down, a lot of others will hold it sideways, and go side to side. However you do it, make sure you are focusing on that edge of the stone, you need to get an "angle" on it, and you need to grind it down to a "girdle" thickness you desire, at that angle. Some people mark the girdle line with a permanent marker, I don't, I just eyeball it.

Something I have learned helps me is, a stone with corners, or points, grind the points first, to the girdle line, this gives you somewhat of a guide for the rest of the stone's sides/edges.

In these 2 photos you can see I have ground the corners down to my girdle line. This girdle line by the way, is not set in stone so to speak, through out the cabbing process, each step takes a little more rock off, layer by layer, so this may change a bit. The angle you see here, is just a guide, the angle you will need is going to depend on the thickness of your pre-form. For very thin stones, your angle may be slightly more slanted inwards (towards the middle of the stone).
OK, so in this picture you see that I have ground down the corners, then gone back and ground the side edges. Do you see the top edge has now moved in towards the middle of the face of the cab? THAT edge of the middle triangle is where we will be focusing our attention now, NOT down by the girdle line as we were before.

For this step, I like to turn my cab, so I can control, and see where I am grinding on the wheel. Since I am now focusing on that inner edge I created, this is how I hold the cab.

It's a little hard to see here, but I am actually able to see what I am grinding holding it this way on the wheel. The goal here is to move that inner edge in to the middle of the stone, so that edge touches each other so to speak.

These 2 photos show how I have met in the middle of the stone, and it is now a level dome. Unfortunetely, with a person being taught in person, hands on, it is almost impossible to show exactly how that happens, but hopefully the photos help you a bit.
For the remaining steps of making cabs, EACH STAGE will be repeated in the same exact way you did the grinding wheel. After each and every stage, dry the stone completely, and check for scratches from the previous stage. The most common areas to have these scratches is right in the middle of the face of the stone, and along the girdle. The hardest ones to get rid of, are the grinding wheel scratches, they are deep, so will require more attention to detail. If you are having a hard time getting rid of the scratches in the middle of the stone, it is highly likely that your dome is not level, and you are not actually hitting the middle of the stone on the wheels.
1. Moving the stones constantly - prevents "flat" spots on your cab - do not let your stone sit too long in one spot on the wheel, keep it moving
2. Make sure to dry the stone, and check to see you have removed all scratches from the previous round
3. Make sure you also remove scratches from the girdle, this presents a cleaner, prettier cab
4.If you are doing them by hand, like I do, clean up the backs of your cab as well, get rid of as many scratches on the backs as you can. If you are using a dop system, you will have to remove the cab from the dop stick in order to do this.
5. If you have scratches, don't assume you can remove them on the next stage, they do not always come out. It gets progressively harder with each stage to remove deep scratches, and at some point, impossible.
6. Scratches on your cabs will create a dull, no shine cab.

Just when you think you have removed all the scratches from your cab.....go over it again, to be sure, on that stage.
100 grit SIC grinding wheel
100 grit SIC belt
220 grit SIC belt
320 grit SIC belt
400 grit SIC belt
600 grit SIC belt

If you are using diamond wheels or belts, these numbers may be different. BUT, the system is the same, the larger the number the finer the grit, and you must progress from course to fine to get a pristine finish.