What Makes a Good Blade?

We have seen ads for blades proclaiming “more diamond!”, or “longer life”. So, how much diamond in the tool is the best amount? How long should a tool last? When we first started developing our own diamond tools in 1995, these were the questions that we were faced with. What we discovered is that the answers are not necessarily obvious. As we developed our first tools what we learned was quite counter-intuitive. Because diamond is thought of to be expensive, often telling people that you are giving them more will make them think that the tool is better. With most of the diamond today being made in CVD furnaces, the cost of diamond is quite small within the tool….most diamond is less than 10 cents a carat, with a 18 inch blade using less than $10 of diamond.

There are a number of variables in the design of a diamond tool, the obvious ones, like the width and height of the blade segments, but then also the not as obvious ones like the diamond concentration, the size of the diamond grit being used, the hardness of the segment matrix and the viscosity and type of cutting fluid.

In our first tools what we learned is that when increasing the amount of diamond in the tool, there comes a point when adding more diamond begins to decrease the effectiveness of the tool. The easiest way to explain what is occurring is to think about an indian bed of nails. Someone can lie on that bed of nails and the pressure on each nail is not enough to puncture the skin since their weight is distributed across the nails evenly. If you were to reduce the number of nails in the bed, at some point it will be quite painful to sit on, and as many of us discovered at some point in our lives, that a single nail in a board, when stepped upon is guaranteed to puncture the skin…even thru a shoe. What this means is that in designing a diamond tool, one has to understand what the ideal concentration of diamond should be for the material being cut.

The second significant thing we learned is around the hardness of the segment matrix. When we first started making our own segments, what we discovered is that most of the segment matrix powder commercially available is much too hard for cutting hard materials. The easiest way to explain this is that when cutting soft materials like concrete and asphalt, the materials and the mud coming off of these materials is much coarser, effectively sand, which is very abrasive to the segment matrix. This abrasive action is what keeps sharpening the tool and keeps it cutting well. If the tool is too soft, it will still cut quite well, but the tool life will be quite short. Conversely, for hard jaspers, agates, petrified wood, etc….the material is very fine grained, and the mud coming off the material is very smooth and fine, which will not produce much wear on a hard matrix, and for this reason, the diamond segment matrix must be quite a bit softer for cutting hard materials.

Lastly, the cutting fluid; often it is discounted to think that a blade will cut the same in low viscosity lapidary oil as it will in thick mineral oil, diesel oil, kerosene or water, etc. Hard materials are best cut using low viscosity lapidary cutting oil so that is what we recommend.

Increasing the viscosity to reduce the misting inside the saw is never a good idea - the blade kerf and clearance is designed for low viscosity oils and using a thick oil will cause significant drag and increased motor loading. This will create heat in both the oil and the stone and can eventually lead to damage of the equipment.

Using water can work if you are cutting softer stones like onyx or soft rhyolites, however, attention must be paid to how well the blade is cutting because without the lubricity of the oil the blade will eventually dull, requiring re-sharpening. Additionally the water will cause damage inside the saw due to corrosion even using corrosion inhibitors.

Using Kerosene or Diesel Oil is also not a good idea as they do not have the lubricity to keep the blade sharp: when the blade becomes dull, the blade force on the stone can rise and begin causing vaporization of the kerosene or diesel, resulting in equipment damage and becoming a high fire hazard. You should never use these as coolants.

The science and art of creating great diamond tools comes from a disciplined approach to selecting and controlling these factors.

Diamond Blade Construction

A diamond blade is made up of two basic parts*

1) The diamond segment or rim

2) The blade core

1) Diamond Segments: The diamond segments or rims are made up of diamond dispersed through a metal matrix

a) The diamond crystals used are typically manufactured or manmade diamonds. Manufactured diamonds are preferred over natural diamonds because crystal shape, size, and strength can be more closely controlled. Various crystal sizes and types of diamonds are used, depending on the specific application

b) The matrix is a metal alloy made of iron, cobalt, nickel, bronze or other metals used in various combinations. The matrix holds the diamond crystals in place, evenly dispersed throughout the segment

c) On the outer edge and sides of the segment or rim, individual diamond crystals are exposed, partially embedded in the metal matrix, or bond. Bond tails which trail behind each exposed diamond, help support the crystals

2) Steel Cores: The steel core is either a high grade heat-treated, tempered steel disc, which is precision ground to size or a non-tempered steel disc

Types of Diamond Blades:

Segmented Blades - These are steel blade cores that have diamond segments welded on with a relief between the segments for increased cutting speed and cooler operation. The Highland Park Segmented blade and the Barranca 303S blade are examples.

Notched Rim Blades - True notched rim blades - like the HP Congo blade - are no longer manufacturered. Current notch rim blades on the market are made from a single continuous diamond matrix bonded to a steel core with notched rim pattern molded into it. The Highland Park Greenline blades and the Barranca 301 blades are examples.  NOTE: Crinkle Blades described below are often deceptively sold as notched rim blades but they are not.

Continous Rim Blades - These are steel core blades that has the diamond segment bonded to the core.  The smaller Highland Park Greenline blades and the Barranca 303C are examples.

*"Crinkle Blades" (Chinese "Green Blades" or "Knurled Blades") - Sometimes misleadingly called "notch rim blades" these are actually steel core blades that have diamond crystal "knurled" or pressed into the metal. They are typically quite thin and initially cut but quickly dull as the diamond is worn off the blade core. Since Crinkle Blades do not contain a segment or diamond plating, their lifespan is extremely short and they cannot be resharped. These blades are specifically imported to be sold to the undiscerning buyer

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