What to Look for in a Diamond Blade
By Frederick M. Hueston
I remember the good ole days when selecting a blade for cutting stone was fairly simple. There where very little choices. You had a blade for granite and one for marble. Pretty simple. Today, with the development of diamond blades the proper selection of a blade for granite, marble, limestone, engineered stone, porcelain, glass etc can be confusing.
How does a fabricator select the proper blade for cutting? The first step is to understand how a diamond blade cuts.
How does a diamond blade cut?
Diamonds are very hard and the hardest mineral known to man. They also do not have the ability to cut. That’s right diamonds do not cut, they work by abrasion. As the diamond blade moves its way through the stone or masonry it grinds the material away. As the diamond grinds it will wear and eventually it will fracture.
These diamonds are bonded to the blade with several types of bonding agents. The way the diamond is bonded will determine how the diamond will wear and hence the type of stone it will cut. It’s beyond the scope of this article to discuss the bonding types however you should be aware that there are hard bonds and soft bonds. The bonding agent is typically metal of varying hardness and metal mixtures. In addition to holding the diamond in place, the bond also controls how the diamond will wear and how slow or fast it will cut and will perform overall. If you look closely at a diamond blade you will see a comet trialing the diamond. This tail is the bonding material wearing. As the bonding wears so will the diamond. The rate of wear is a direct relationship to how the diamond is bonded.
In general a hard bond is used for soft stones and masonry and a soft bond is used for hard stones and masonry. At first this doesn’t make sense until you realize that a soft bond is need to expose more diamond to cut harder stones. Whereas a hardbond doesn’t need to wear away as fast with a soft stone.
Diamond Segments
There are numerous ways to attach the bond and diamond to a metal or composite disc. The following is an explanation to help you select the proper blade.
The diamond segments can be attached to the blade in several ways.
Brazing is similar to soldering where a silver solder is heated and bonds the segment to the blade
Welding uses heat as well but the heat is so intense that it melts the metal and the segment together
Mechanical bonding physically locks the segment into the blade with some type of a notch.
What blade to Buy
As you can see understanding diamond blades can require a degree in metallurgy. So, if you don’t plan spending the next four years getting such a degree how does the fabricator determine which blade works best for the type of stone you are cutting?
Your first step is to ask the manufacturer or distributor which blade they recommend for a particular stone or masonry type. Many of them are very knowledgeable but this doesn’t mean you will always get the best advice. Ask other fabricator which blades they use. Go to the various stone fabrication forums and post a question.
The second and perhaps the most important thing to consider when purchasing a good blade are the diameter of the blade and the speed of your saw. This is perhaps the most overlooked parameter when it comes to choosing the proper blade. Here is how to determine the proper blade diameter for your saw
A good saw manufacturer will tell you what size blade to buy for optimal cutting of different stones. Optimal cutting is determined by calculating the surface feet per minute. To calculate the s.f.p.m. (surface feet per minute) you need to know the r.p.m. (revolutions per minute), the diameter of the blade, and the numeric value for pi. You can also determine the diameter requirements by knowing the recommended s.f.p.m. for the stone and r.p.m. of your saw.
S.F.P.M.= Pi x R.P.M. x Blade Diameter
Or
Blade Diameter = S.F.P.M.
Pi x R.P.M.
*(Pi = 3.14)
Marble
A reputable diamond blade salesperson will recommend a different blade for cutting marble than used for cutting granite. The difference will be in the diamond concentration, the bond (material used to hold the diamonds in place), and the diameter if your saw has only one cutting speed. Marble requires more surface feet per minute (6,000 to 8,500 s.f.p.m.),[i] so for single speed saws your marble blade will be larger than your granite blade.
Granite
Granite requires less surface feet per minute (4,500 to 6,500 s.f.p.m.), so for a single speed saw your granite blade will be smaller than your marble blade. It is also much harder than marble and requires a harder bond to make the blade last longer. Using a smaller blade on harder granite makes the blade cut softer.[ii]
Limestone
Limestone requires much more surface feet per minute (7,500 to 10,000 s.f.p.m.)[iii]. For a single speed saw your limestone blade will be larger than your granite or marble blade.
Engineered Stone
Most engineered stone will require the same surface feet per minute as granite(4500-6500 s.f.p.m.). However the resins contained in engineered stone can be a concern with certain blade types. For this reason, make sure you use a blade that is designed for engineered stone. There are blades available that will work on granite and engineered stone.
Segmented (friction)
Most blades for your permanent saw are segmented. The diamonds are welded to a friction core in segments with gaps between them. This feature will help the blade cut faster, stay cooler, last longer, and remove the slurry (muck).
Turbo (staggered segments)
These blades are normally used on portable saws. The diamond segments are staggered and overlapping. Because the segments are staggered, the blade operates similarly to the segmented.
Continuous Rim
These blades are also normally used on portable saws. The blade has, as its name indicates, a continuous diamond rim without staggers or gaps. We will use this type of blade on our big saw with a soft bond for smooth miter cuts and joint cuts. The disadvantage of this is that the blade cuts slower, hotter, wears faster, and does not assist in the removal of slurry.
These are just some of the important parameters when it comes to diamond blades. Here are some other factors that need to be considered:
All diamonds are not the same and are available in different grades, hardness and grit sizes.
Diamond concentration is also important.
The feeding speed of your saw is important. If the feeding speed is too fast you take the chance of breaking a segment.
Granite is classified into five types based on there volume of quartz and each class will have a recommendation by the blade manufacture. For example Class 1 granite may have a speed of up to 600cm2 per minute.
There are also different segment types such as three layer, normal and many others
There are various types of steel cores such as normal core which is a high grade heat treated. Tempered steel for high demands on stability and wear resistance. The core is also responsible for damping wobbling. Many blades are now silent core. A silent core consists of two sheets of steel with a sheet of copper between them.
The list goes on and on and in no way is the information above complete. Also the information is based on blades for bridge saws. Hand saws, grinders etc are a whole different matter when it comes to diamond blades. The information also does not apply to dry cutting.
TIP
Did you ever wonder why there is a directional arrow on most diamond blades?
Many diamond blades are broke in during the manufacturing process. If you mount the blade with the arrow in the opposite direction it can cause premature wear of the blade since it may pull out some of the diamonds.
[i] Joe Lauer – Park Industries, Inc. – St. Cloud, MN. – Phone interview on February 10, 1997.
[ii] Joe Lauer – February 10, 1997.
[iii] Joe Lauer – February 10, 1997.
