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Diamond Grinding Saw Blades


Lowell Freeborn

The first question you should ask yourself is: What do I expect from a diamond wheel? Your answer should be a wheel that removes carbide fast and cool. Think this over very carefully and do not get talked into purchasing a wheel simply because it will last longer than any other. This is a very false economy and you will pay in lost time as well as in cracked and poorly ground carbide.  For more articles on Grinding or Sharpening Saw Blades. 

One way of arriving at diamond wheel cost is to add the cost of the wheel and the cost of the labor required to produce a certain dollar volume of work. There can be a point of no return when too much wheel is used or too much labor.  Bear in mind that if you grind one saw for $10.00 in 15 minutes and use $2.00 worth of diamond, you are far better off than to grind the same saw in 30 minutes and use $1.00 worth of diamond.  This lesson in economics is only meant to impress you with the need for a practical approach to the use of diamond wheels and the fact that labor is a far more costly part of the grinding job. 

There is one fact that you must be aware of; you have to use up diamonds to grind carbide. It is up to you to figure a successful proportion of diamond and labor costs that will give you the return you are looking for. 

Some 40 years ago, manufactured diamonds were introduced to industry, and since that time its use has expanded tremendously. Today these diamonds are more uniform in size and resist shock better than natural diamonds. Of course the metal coating of diamonds with nickel and copper has also added greatly to their life.  It is generally accepted that copper coated diamonds are best suited for dry grinding, and nickel coated diamonds are best suited for wet grinding. Even though coated diamonds last longer, they do create more grinding heat and do not grind as cool as plain diamonds do. 

There are two major bond types; resinoid and metal. Metal bonds work well on non-metallic materials such as glass, ceramic, stone, etc. but do not grind carbide efficiently. Due to the fact that metal bonds are too hard and severe for carbide grinding, we shall limit our discussion to resin bonds. 

Diamond wheel manufacturers make resin bonds in numerous grades and hardnesses. Diamonds also come in different grades and in different coarsenesses.  You must carefully select the wheels that work best for your operation.  Generally, wheels with 150 grit, 75 concentration, and R hardness are used for regular grinding. 

Finer grit wheels will give better finishes on the carbide and improve the cut quality, lengthen life between sharpening, and require less power than saws with rough grinds. These wheels, however, grind slower and require more time to finish a saw.  Again you will have to be the judge of your customer's requirements. 

If a saw pushes hard and tends to wobble in the cut, the problem can often be traced to rough grinding. By using a fine wheel and putting a good finish on the saw teeth, it is often possible to solve this saw problem.

There is a definite difference in the "grindability" of various grades of carbide.  Some are harder on diamond wheels than others.  The greater the cobalt content in the carbide, the greater the diamond wheel wear will be.  In other words, the softer grades of carbide cause greater diamond wheel wear. 

One very important consideration is the concentration of diamond in the wheel. There is no doubt that an increase of diamond up to 125% greatly improves the grinding performance.  The extended life of these diamond wheels outweighs the cost.  Wheels with 50% or lower concentration of diamond are very poor performers and should be avoided. 

The most important operating variables are wheel speed and traverse rate.  Also important are wheel rim width and diamond concentration. These variables can affect your costs considerably and should be watched carefully and a controlled evaluation study should be made for each variable. 

It should be emphatically stated that two thirds of  "On The Job Testing" is evaluated by operator opinion, and that this is the most common method of testing used today.  Operator opinion is certainly important but it should not be used exclusively in place of some good old fashioned records with facts and figures. 

The rapid wear of diamond wheels can be attributed to many things;  

1. Heat causes breakdown of the bond and rapid wheel breakdown. The heat is caused by too fast a feed and too much wheel contact.  Wet grinding helps this problem, but the main thing is to let the wheel cut without forcing it too much. 

2. Dry grinding causes more wear than wet grinding, so if you are dry grinding you must grind slower in order to keep your wear down. 

3. The grit size of the diamond makes a big difference in wear and stock removal.  The coarser grits yield rougher finishes but stay in the bond better and remove stock faster and cooler. 

4. Diamond wheels sometimes load due to improper use and can act dull and grind very hot.  Wheel dressing will remove this build up but it is wasteful and should not be necessary if the correct wheel is used on the job.  If wheels must be dressed, the dressing should be done carefully so as to avoid excessive diamond loss. 

For the sake of economy it is often necessary to rough grind a saw and then finish it with fine grit wheels in the 400 or 500 grit size. This is particularly true if making a new saw or retipping an old one.  

A good rule of thumb to use for arriving at end cost is to have your labor cost equal your diamond wheel cost.  This is an easy way of determining the efficiency of your operation. 

Diamonds are a man's best friend when grinding a carbide saw, but you cannot do a good job in a minimum amount of time without using some diamond to do it.  Just be sure that you do a first class job and can make a profit using labor and diamonds in relation to the price of the job.