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Unread 05-19-2013, 01:01 PM   #8
John Bridge
Join Date: Mar 2001
Location: Rosanky, Texas
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Dressing diamond saw blades by Martin Dykmans

I think we all know what happens to our blades. We cut certain materials and the more we cut them, the "duller" the blade gets. Porcelain is the 1st thing that comes to mind. Some hard granites can also have you pulling hair as the cut speeds drops. But why is this happening when we aren't having these problems with soft-body tiles or limestone etc?

The blades we use are designed to cut a specific hardness group. The metal matrix which holds the diamonds is designed to wear appropriately for this or that hardness group. Most of our blades are an alloy of steel/nickel/(assorted other metals). A blade suited specifically for marble/limestone will have a brass/other alloy. Without getting into complexities of why these alloys are chosen, the reason is simple. The material being cut is what keeps diamonds exposed by wearing away at the matrix, so that as exposed diamonds are worn-down, fresh diamonds are being exposed to replace them. I think we all know this, but for the sake of posterity let me drone on...

What happens when we use a blade designed for cutting one hardness group on a different hardness group? "Glazing" is the generally used term for using a blade designed for a softer group on a harder group, and visa-versa; harder on softer. But why? Using a "hard" blade on soft makes sense; the softer material can't remove the hard matrix. On the reverse; "softer" blade cutting harder material, you would think the harder material would also work better for removing matrix. Now we get to the 2nd difference between diamond blades: specific diamond hardness. We have all been led to believe that diamonds are the hardest substance at a 10 on the Mohr scale. Nothing else is as hard. What isn't as common knowledge is that there are levels of hardness at 10: 10, 10.1, 10.2, 10.3....... Generally the hardest diamonds are reserved for the gemstone industry. How do you polish a diamond? With harder diamond grit of course!

So another factor in a blade designed for cutting the hardest materials is the specific hardness of the diamonds set in the matrix. All diamonds are dulled as cutting takes place. the cutting surface becomes rounded, diminishing the "cut" activity as a harder material is forced through a softer material. In this state, the blade encounters a resistance to spinning, as the slot it is cutting begins to bind on the blade. The exposed diamond becomes almost flush with the matrix. Why? because the material being cut has reduced to a fine "sawdust" where it was once being gouged out in larger particles. Let's store that concept for now.....

Entering the world of the glazed blade, let's look for a minute at another abrasion function, for that truly is the way a diamond saw "cuts": by abrasion. A very necessary function of stonework is abrasion. Sandpaper, grindstones. A grindstone is kind of like a really thick sandpaper in a way. They too have glazing problems. The abrasive has become dull. It is developing a residue build-up you can see on the grindstone, keeping the abrasive from contacting the material being abraded. Net affect from continued attempt at grinding leads to lots of heat being generated but almost zero "cutting" being accomplished. So we must dress the stone, which below I show the tool used and a close-up of what does the dressing.

A stone dresser is held against the grindstone loosely, taken away to stop the spurs from spinning, re-applied over and over, across the face of the stone. If you have never used one of these, you would be amazed at how fast they work, and how much material they are taking off the stone. But why? the spurs/discs are just a hardened steel, much softer than the stone. Actually, if you held one of the spurs against the stone without it spinning, you will watch the spur be reduced to nothing in no time. Light bulb time: the spinning is the key, as is the spur design. That, when combined with the different rates of speed between the stone and the spurs creates the dressing action: the spurs impact the grindstone quickly and depart the grindstone, creating a gouging of the grindstone as small chunks are knocked-off. The stone may be harder than the steel, but it is also more brittle to impact. This is easily evidenced by dropping a piece of glass (harder) and a lead ball (softer), glass breaks and the lovely properties of metal only makes them dent.

So why don't they have a neat little dresser for diamond blades like the grindstone dresser? Well they do, but it doesn't look like it. A Diamond Blade Dressing Block works with the same principle as the grindstone dresser but a different format.

When a diamond blade cuts a slot (or saw kerf), the space between the blade and the slot walls is very limited. A diamond blade dressing block is made-up of loosely adhered particles of a very visible size; very close to the size of the sand in our fat or deck mud. Light bulb time again

All that leads up to what the headstone guy told me back in 1988 when we were opening a stone fabrication shop. I'm going to paraphrase here:

'The best thing to use to de-glaze your blades is to mix-up some of you tile guys' deck mud and make a brick out of it. If you can use sand made from crushed rock all the better, but regular beach sand works too. Then you run the blade through it over and over, slower at 1st and faster and faster until you are forcing the cut as fast as you can make it cut.'

What happens is that the loosely held sand particles get knocked loose rather than being cut (abraded), and get caught in the saw kerf, rolling between the kerf walls and the blade gouging out the matrix and they go until expelled. The matrix is quickly worn away, the dull diamonds fall out, and nice fresh, sharp diamonds become exposed without being dulled by the cutting process. Alacazam; dressed blade cuts like brand new.

Thank you headstone guy. I guess something was learned in what he told me he was 5th generation Italian Stone Worker handed-down trade secrets. WE SALUTE YOU

Now you can go out and buy yourself an actual Diamond Blade Dressing Block. They are ideal. But why not just use what is readily available, costs nothing, and works (pretty much) just as good as the expensive dressing block? If you don't have any dried chunks of deck mud, fat mud or stucco slag work ALMOST as good. And it's all better than any kind of brick, but cinder block is next in line for a workable blade dresser...

Martin Dykmans
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