The triple chip tooth blade pattern that eats through tough materials has been the workhorse of the sawing industry for decades. However, in the early 1990s, manufacturers in Europe began playing with the triple chip tooth design to find more effective ways of cutting specific materials, especially exotic alloys.
No matter the operation or material, the goal is always to achieve faster cutting with less feed force and longer blade life. When exotic alloys enter the equation, tooth design and choice of blade material become more important. For example, the aerospace and healthcare industries use materials that almost always demand carbide tipped blades for cutting. Inconels 718 and 625, nickel alloys, Hastelloy, cobalt chrome and titanium – these are all metals that are hard to cut and are better managed using carbide blades rather than bi-metal blades.
Gene Ramsdell, a sawing expert and metallurgist with Starrett Saws, says coming up with new designs for carbide tipped blades is part of Starrett’s process in bringing more efficiency to customers. Admittedly, Ramsdell says Starrett, known best in the northern hemisphere as a precision tool manufacturer, got a relatively late start to bringing carbide into the mix with its saw blade designs.
“Several years ago, we started research on developing more blade types,” Ramsdell says, adding that the Advanz multi-chip 7 (MC7) blade, Starrett’s answer to the triple chip tooth blade, was designed to cut seven small chips over the course of the tooth pattern. “It allows for smaller chip width per tooth, which results in less wear on the tooth. And because there are effectively fewer teeth of the same type in a given pattern, the MC7 is creating a thinner, deeper cut. Same chip load, different cross sectional shape.”
Starrett also developed the Advanz multi-chip 5 (MC5) blade that performs slightly less efficient cutting than the MC7 but can take more abuse in applications such as those that involve harder nickel alloys or less rigid machines. The design allows the chip load to be spread out over five teeth, facilitating longer blade life.
Developing tooth geometries, such as on the MC7 blade, allows for less wear, straighter cuts and longer blade life. Manufacturers working with exotic alloys need every break they can get, especially considering the cost of the raw materials, which when cut improperly can lead to unwanted overhead. Ramsdell says, for example, that the Inconel 718 or titanium, both of which are among the most expensive, materials, must be cut correctly and not turned into scrap due to poor blade performance.
“They really can’t afford to throw away pounds of materials when they’re in excess of $15 and $20 a pound,” he explains. “They need a blade that helps them maintain the straightness of the cut. The surface finish has to be smooth so there are less secondary operations, such as milling or grinding. They can use the as-cut surface. That’s important, and it goes into the cost per cut.”
Ramsdell says the MC series addresses those concerns. The MC7 and MC5 blades utilize an unset tooth arrangement, which means the teeth are ground in a way that presents different areas of contact to produce a chip. The end result of the cut is a near-mirror finish on the material.
“The MC7 will cut anything,” Ramsdell flatly states. “It can cut hot-rolled billets or age-hardened products, which may be up into the Rockwell HRC 30 to 40 range. That hardness really beats up on a bi-metal blade, but it’s the perfect spot to go into with carbide.”
The MC7 blade does anything a triple chip tooth blade does, but more efficiently. However, rather than pigeon hole the MC7 blade into exotic alloy-only use, Ramsdell says Starrett is careful to note that it is also a great blade for all ferrous metals.
Research and test
The MC7 design was two years in the making. However, Ramsdell says it’s still an ongoing process. The R&D team is constantly brainstorming in the company’s North Carolina plant, which is also the location of the company’s saw division.
“We run a series of benchmarking tests with other competitors’ blades on different materials,” Ramsdell says. “We find out what performs well and what doesn’t.”
Kyle Wissing, product development engineer at Starrett, says to research blade life without wasting expensive cutting material, Starrett uses a bandsaw fitted with a load cell and force gauge to measure side width pressure to determine if the material will be forced out of alignment during the cut.
“By measuring the force imparted on the workpiece,” Wissing explains, “we can watch for trends and make predictions about the life of a blade. For example, after several cuts of a small bar of stainless steel, the MC7 blade was found to require 10 to 20 less force than the Starrett TS (triple chip) blade and 5 lbs. less than the MC5 blade. By controlling for machine parameters, such as band speed, feed rate and coolant, different styles of blade can be ranked by performance.”
Ramsdell notes that there are different ways to approach wear on blades. Some shops want to cut material as fast as possible without regard for the life of the blade. The cost per cut might be worth it for these shops because they’re pumping out twice as many parts as they would be by slowing down and prolonging blade life.
To further research, the R&D team sends out samples of its finished product to laboratories that utilize scanning electron microscopes to get an up-close look at the ground finish on the tooth tips. To get a quick look at its test blades, Starrett has an optics division located in California that produces precision optical products. The goal is to minimize any jagged peaks of the cutting edge and make the surface finish smoother and less likely to fracture. Carbide is much more prone to fracturing just due to high hardness.
“On the initial cuts with the bandsaw, it’s important that you try to prevent this micro fracture from occurring,” Ramsdell notes.
Single-point tooling, Ramsdell says, may use a particularly hard grade of carbide because there is constant contact with the tool and workpiece. However, with bandsaw applications, the teeth are making intermittent contact with the material, so there is more impact that requires a tougher grade of carbide based on binder content and grain size. Starrett uses several grades of carbide aimed for specific styles of saws. For instance, the MC7 blade uses the Vickers 1,600 sub-micron type, which is a good, all-around grade that is tough and wears well.
Vibration is another factor in carbide blade performance.
“Vibration is the killer in carbide,” Ramsdell warns. “The tooth has to handle the impact and the machine has to be sturdy enough to dampen any vibration.”
Vibration can be generated by the transmission that turns the blade.
It can also occur when the bearings in the bandsaw wheels aren’t high quality. The clamping mechanism must be spot on, and the down feed and band speed must be tweaked exactly right. Furthermore, higher tensile stresses are involved with bandsaw work, which is necessary to hold the blade tight between the guides. These guides must be maintained and replaced or the quality of the cuts will be compromised.
But all of these issues can’t overcome the issues put forward by a bad saw operator or poorly maintained machine. Ramsdell says there are a number of instances where these problems are evident, and they are ones that can “make or break your business.”
“A good saw operator will know if the operation doesn’t sound right,” Ramsdell says. “If it’s squealing or groaning, or you put your fingers on the side of the machine and you feel a different vibration, that is a problem. The operator has to keep his ear to his work, so to speak, and try to maintain the machine.”
The right application
Bi-metal blades have teeth made of high-speed steel bonded to a carbon steel base. They have a hardness rating of around Rockwell HRC 68, which means they are less likely to chip than a carbide blade.
“Here is where the tradeoff comes,” Ramsdell says. “If you have a machine that is poorly maintained, you might be wasting your money buying a carbide blade because, chances are, the blade won’t see its useful life just due to the condition of the machine.”
Where carbide really shines, Ramsdell says, is on stainless steel and exotic alloys. Production rates can triple what manufacturers using bi-metal blades are able to achieve.
“The whole industry has evolved in the last 15 to 20 years in cutting exotic and aerospace materials,” he says. “It’s almost a non-issue when it comes to increasing productivity.”
Ramsdell ends by saying Starrett is here to help solve difficult bandsaw cutting applications and it has the technical assistance available to do it.
“We can help via phone or internet,” he says. “We also have saw service engineers throughout North America for onsite visits. We want to help customers.”