DIAMOND BRAZED CUPS - FAQ

1. I'm wondering about how many spheres can be ground before discarding or refreshing the diamond.
Answer: It depends! There are many variables to consider.
a. Hardness of the rocks
b. Size of the cups
c. Speed of cup rotation (I recommend between 150 and 200 RPM)
d. Tension on the cups
e. Mesh size and concentration of diamond in the matrix.
Experience so far has shown that in excess of 100 balls at a minimum can be ground before renewal of course diamond matrix is required using the diamond rods we sell. The fine mesh cups last even longer. I brazed a set of 3 inch 600 mesh cups 10 years ago and they are only slightly worn as of January 2010. They seem to last forever.

2. Can you apply more diamond as the original brazing wears away or do you have to toss the old brazed cups and replace them completely?
Answer: Once brazed, the cups can be renewed with new diamond practically forever. The second brazed will meld and blend with whatever is leftover from the first braze. The only thing you have to "toss" is the grindings in the drip pan under the cups.

3.What diamond mesh size should I use as a roughing grade or should I use a medium grade to try it out first before going completely diamond?
Answer: The rods come in a variety of mesh sizes designed to meet standard lapidary techniques. Here is a list of popular sizes and their uses:
a. 30/40 mesh - Used for course(DR01) grinding of soft stones such as Marble, Onyx or Granite. Stones of 5 hardness (Mohs) or less. The reason is that the harder stones will crack and break the diamond bits out of the matrix. You must then re-sharpen the cup using loose grit to expose more diamond.
b. 40/50 mesh - This is a good all around course(DR01) grind compromise between speed of cutting and longevity of the cups. Most Lapidary applications can use this mesh size.
c. 50/60 mesh - Used to course(DR01) grind harder agates and Petrified Wood. Provides good longevity of cups without excessive scoring of the stone. I've made a hundred spheres before re-brazing is required with this mesh size.
d. 140/170 mesh - Use as a medium smoothing step (DR01) `to remove scratches made by 30/40 mesh grinding if necessary. Use this size to work Jasper that tends to flake and chip. Not needed in most applications.
e. 220 mesh - Use as a medium smoothing step (DR02) to remove scratches made by course (40/50, 50/60) mesh grinding if necessary.
f. 600 mesh - This size will provide a semi-polish (pre-polish DR02) before preceding to the final polish. Most of the time I've been able to go directly from course grind to this mesh with great results. It's amazing how much slurry is produced by the 600 mesh cups rotating at 157 RPM.

4. I have my own torch and have some existing worn-in cups. Can they be brazed?
Answer: Yes! Standard brazing techniques are used to apply the rod to the steel cups. A word of CAUTION! Do not braze GALVANIZED cups without using the proper breathing (Carbon Filtered) mask. Galvanized cups heated with a torch produce toxic fumes. Try to remove as much of the galvanize as possible before heating.

5. Do the grinding cups need to be beveled inside?
Answer: The cups will perform better and are easier to adjust if beveled before brazing. I recommend a 22 degree angle about 5/16's of an inch wide inside the cup. You can simply pre-grind the cup using silicon carbide until you get the desired beveled surface. Otherwise, visit your local Mill Shop.

6. How well do I have to make the weld on the cup?
Answer: The weld doesn't have to be pretty or even smooth. The wear from the stone you are grinding will soon make the surface very smooth. It will take several spheres of various sizes to smooth out the weld from edge to edge. A deposit depth of at least 1/8th inch is recommended. The cups should be pre-heated to a very hot state before attempting the brazing procedure. This makes for a better flow of the melted matrix.

7. How do I tell when to renew the diamond braze?
Answer: When you see the steel cup surface breaking through the matrix it's time to re-braze the cup. In most cases the bottom inside will wear through first (Point of most wear). The cup will still grind on a larger sphere until you see the steel underneath breaking through.

8. My cups seem to have stopped cutting. What's wrong?
Answer: Just as in the case of a dull diamond saw blade, the cups will sometimes glaze over and new diamond needs to be exposed. Simply apply a few shakes of silicon carbide of the same mesh size as the cups to expose more (new) diamond. Once you see the slurry return after the S/C has washed away you have applied enough loose grit to sharpen the cups. This should not be necessary very often. Another effective way of getting the cups to cut once more is to put in a different sized ball. I've found that this helps keep the wear more even as well.

9. How much water should I use on the sphere during grinding and polishing?
Answer: You need to keep a steady drip (I recommend one drip every two seconds) on the sphere during grinding to flush out the loose particles during the grinding phase. If the sphere is covered with slurry then you need to increase the drip just a bit. When polishing I start out with a light drip on the sphere using Velcro diamond pads inside of PVC pipe cups. After the spots are gone, I start with 200 or 300 mesh advancing to 500 , 1000, 1500 for about 20 minutes each step and then 3000. After a half hour the sphere should have a bright polish at 3000 mesh pads. You can go higher in mesh size but the result is hard to see any improvement in the shine. I've been experimenting with 8000 mesh pads and they do make an improvement on most agates and hard stones.

10. How many rods will it take to braze my cups?
Answer: It depends on the cup size and depth of weld deposit. I generally put 1/8th inch deep welds on approximately 5/16th inch wide beveled cups which takes 1 rod per cup for 1 ¼ inch cups. It takes about 1.25 to 1.5 rods to braze each 2 inch cup but you can go a little thinner on the depth and stretch it out. The rods are 15 inches long for all mesh sizes. Please call (see the "About Us" tab on the Home Page) if you have more questions concerning the brazing process.

11. Why does the cup wear through in just one spot (usually near the bottom of the circle)?
Answer: Unless you grind several different size spheres over time the abrasive diamond matrix will be depleted in a single spot. A small sphere size relative to the cup size will wear on the inner part of the cup were as a larger sphere size will wear on the outer ring of the cup. Even though the matrix has worn through in a particular spot, the cup will still work on a different sized sphere.

Brazing Tips
Over time I’ve noticed some things using the brazing rods I’d like to pass on in hopes of helping the folks out there braze their own cups. First off, I have had varied success using the finer mesh sizes, as the diamonds tend to clump up and make a resulting braze on the cup ring that resembles cornbread.The small size of the diamonds makes them want to stick together. I’ve found that this is made worse by having the heat too hot from your torch and the cup metal too cold. Also, if you heat one specific spot too long the diamonds appear to loose their coatings making the mixing of the diamonds with the melted matrix difficult. One way I’ve found to minimize this is to gently stir the melt with the end of my brazing rod as I go around the cup ring. The stirring action appears to make a more consistent mix on the cup ring by breaking up the little clumps. I’ve found that it is difficult to get the torch heat just right for a smooth braze surface on the very small mesh diamond rods. This has only been true with the finer mesh sizes as the larger diamonds blend very well with the hot, melted matrix. Too much heat and the diamonds explode into little shooting stars (a little bit of this is not a problem). If your cup isn’t hot enough when you start brazing the melt cools too quickly and makes for a very rough braze surface. I have had some success in improving the appearance of the finished braze by dipping the end of the hot rod into a can of Technical Borax flux powder (30 mesh). I only do this when it appears the diamonds are having trouble blending into the melt.
Another problem I’ve encountered is a variation in the quality of the steel cups I’ve tried to braze. Some of them appear to have a component that interferes with the brazing process. I’ve noticed this problem on cups made in China more so than those made in Thailand. The problem presents itself with lots of holes in the matrix as if there is a gas emitting from the steel. Cups should be clean and totally clean from oil or grease before brazing them. I use a Craftsman 5415 D-1 Acetylene and Oxygen torch and a neutral flame on my cups.
Neutral Flame
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