by Jason Schofield
Extending the life of saw blades
A cleaner finish, faster throughput and longer blade life are all characteristics of a cold saw at work, but a saw is only as good as the blade it cuts with. One unique advantage and the biggest cost savings of using a cold saw is the long lifespan of the blade.
Even with extensive use, a properly maintained cold saw blade should last a long time. It can endure as many as 800 to 1,000 cuts before needing to be re-sharpened and it can be sharpened 30 to 40 times during its lifespan; keep in mind the diameter of the blade is reduced with every sharpening because a small amount of material is ground from the rim each time.
There are no general purpose or universal cold saw blades, so it’s crucial to choose one that’s appropriate for the material being cut. Most cold saw blades are made out of M2 high speed steel due to their abrasion resistance and hardness and are commonly coated with a steam oxide or black oxide, which helps them hold their edges and prevents galling as the blade passes through the material.
How to choose a blade
Large or small solids and thick or thin walled tubing each require different types of blades. The proper blade and RPM for the material being cut is critical. To determine which is right for your application, evaluate tooth geometry, pitch and bevel of the blade. Also consider the RPM and speed of the cut, the material hardness and how rigid the material is clamped.
Pitch is the size of one saw blade tooth or the distance from one tip to the next in millimeters. A blade with more teeth has a smaller pitch and one with fewer teeth has a larger pitch. Solid materials need to be cut at a slower rpm with three to five teeth making contact with the material. When cutting tubing, the wall thickness determines the cut speed and pitch. Thick-walled tube should be processed at a slower rpm and the pitch should be smaller than the wall thickness, and thin-walled tube should be cut at a higher rpm and the pitch should be as small as possible.
Beyond pitch, cold saw blades have teeth with various types of bevels or notches—including alternate, triple chip, notch grind and round grind. Triple chip and alternate grinds are the most common, but the material you are cutting will ultimately determine the blade you will use.
Change blades correctly
Develop a specific procedure to follow each time a blade is changed to ensure correctness and consistency. There are two simple things that are often overlooked but need to be done every time a blade is changed. We call them backlash and dirty flange.
A saw blade is driven by the pins in the flange. When changing blades, the backlash must be removed, which is simple to do. After putting the blade on the machine, but before tightening the bolt on the flange, lift up on the front of the blade and hold it there until the bolt is tight. This keeps the pin-holes in and the blade against the pins in the flange. If a blade breaks through a pin-hole, it is because the backlash was not removed.
If metal chips are allowed to fall in between the flange and saw spindle, the flange becomes dirty, which will cause the blade to wobble during cutting. A saw blade cannot run true and cut properly with a dirty flange, and it can contribute to other problems as well, including pickup. Pickup occurs when the material being cut has bonded to both sides of a saw blade tooth, making it wider or thicker than the blade is supposed to be. Each time the thicker tooth passes through the material, it will grab the material and cause the saw head to jump.
Pickup worsens each time that tooth passes through the material until, finally, the amount of material collected will jam the blade in the material and either rip a chunk out of the blade or break the blade into pieces. Pickup can be caused by a number of things: dirty flanges, dull blades, weak coolant, the wrong coolant, use of the wrong blade or running the blade at the wrong speed.
It can be felt by dragging your fingernail over the side of the tooth. If you feel pickup on the blade, stop using it or you risk a broken blade. The best way to eliminate pickup is to re-sharpen the blade. Have your cold saw blades professionally sharpened by a reputable sharpening service, because as stated previously, a saw is only as good as the blade it cuts with.
To prolong the life of saw blades, read the operator’s manual for the cold saw, which contains important safety tips, operating procedures and maintenance information. Then, when mounting a new or re-sharpened blade, be mindful of the extremely sharp edges and remember to break in the blade by feeding it slowly through the material for the first three or four cuts. Also, use a good coolant mixed to the proper strength. Failure to use adequate lubrication will result in unnecessary friction causing the blade to generate heat and become dull faster.
Knowing the proper force required to make a cut is also important for a long blade life. Letting the saw blade do its job by not forcing it into the material will make a big difference in not only blade life, but in the quality of the cut. Applying excess pressure does not yield a better or faster cut; instead it adds unnecessary stress on the blade. Listen to your machine and understand its RPM and cut speed options, feed rates and chip load to get the most out of your saw and its blades. SMT
Jason Schofield, Engineering, Scotchman Industries.