Fabrication shops use band saws for many different types of cutting on a variety of materials. No one blade is a perfect fit for all applications, so what must you take into consideration in selecting the blade that is best for your needs? We spoke to experts Russell J. Chibe (left), regional sales manager, Cosen Saws, North America, and Jay K. Gordon (right), North America sales manager, saws and hand tools, The L.S. Starrett Company, to help you build a band saw purchasing strategy that delivers the lowest cost per cut while maintaining acceptable levels of finish.
- When it comes to bandsaw blade thickness, what needs to be considered in selecting a thickness that will provide the straightest cut without causing issues with the side guides or roller bearings?
Generally speaking, the thicker a blade, the more beam strength it develops. Blades with greater beam strengths can withstand a higher feed rate, resulting in straighter and more accurate cuts, explains Chibe. With that being said, most blade sizes are pre-determined by saw manufacturers with very few options to change blade sizes. So, in most cases there is no decision to be made other than when you purchase the machine.
2. Blades are made from a variety of materials. When are bimetal blades the best option?
If you’re cutting steel of any kind, bimetal is typically the first choice, asserts Gordon. There are a lot of materials you can cut well with bimetal blades such as general steels, structural steels, and carbon steels, and even some stainless steels and titanium.
Keeping in mind that material and cutting ability are the primary considerations, Chibe advises that bimetal blades tend to be more cost-effective for shops compared to carbide-tipped blades.
“In some instances, it’s not worth it for a shop to purchase a carbide tipped blade. If you’re cutting mild steels and you’re cutting in the back of a fab shop, or you’re cutting in a maintenance area of a plant, are you really going to need carbide tipped blades? That’s where a bimetal blade really earns its keep. Bimetal can do quite a few things using proper feeds and speeds,” Chibe points out.
Bimetal blades typically have 67/69 Rockwell C tooth hardness and so can be used in materials up to 40/45 Rockwell C. “That’s not to say they won’t cut a bit above that, but then the cost per cut goes way up. For example, if you’re cutting Inconel and trying it with a bimetal blade, will you cut it? Probably, but it may take a long time and it will likely wear out the blade,” Gordon says.
But bimetal blades will not cut everything well. “Once you get above 45 Rockwell C you need to start thinking about carbide tipped blades, because carbide itself can go up to 50+ Rockwell with a positive rake,” Gordon says. “In many cases, there are shops cutting a wide range of materials, everything from aluminum to stainless steel and all the carbons in between. But changing a blade from bimetal to carbide may not make sense if it is just for a few cuts.”
3. So when should a carbide-tipped blade be considered the best option and what advantages does it provide?
Carbide blades, which have approximately 100 Rockwell C tooth hardness, offer several advantages, including long life and fast cutting, says Gordon. Another advantage is cut finish. A triple-chip carbide, which has many facets ground into the carbide teeth, will give you a really nice finish, adds Chibe.
“I’ve seen some mirror finishes,” Chibe confides. When cutting with a bimetal blade, you’re going to see more of the striations through the work. If finish is important to you, triple chip carbide will achieve the best finish.
The disadvantage with carbide-tipped blades is they don’t like vibration. So, if you are trying to decide whether to go up to a carbide-tipped blade, there are decisions to consider, Gordon cautions.
“Do you have a saw that can handle a carbide blade? You can put a carbide blade on pretty much any saw that will take the width of it. But if you have a 40-year-old saw that is shaking and rattling, it’s probably not going to work very well,” Gordon says. “In that instance, the carbide blade is going to cost you significantly more than the bimetal, and your machine is going to be what tears up the blade (even more so than the material).”
Gordon adds that if you’re looking to purchase a saw machine, and you’re going to be primarily cutting hard materials, there are saws that are specifically designed for carbide.
“They are heavyweight, produce no vibration, and can run at much faster speeds–all the things that carbide likes,” Gordon says. “For production operations, the decision to use carbide is made because they are not getting enough pieces on the floor. The bimetal blade may not be cutting fast enough, or blade life is not good. Since changing blades takes time, carbide-tipped can last longer and reduce blade changes.
4. Blade teeth are available in several shapes and settings, which can be somewhat confusing. What are the most important things to consider in deciding which tooth size and tooth setting is the best option for a particular application?
With tooth settings, one set on most blades is the standard offered from most blade manufacturers. The other option offered is an extra heavy-set blade. “The reason you would pick an extra heavy-set blade is to help eliminate pinching problems with some materials,” says Chibe, explaining that when you cut through materials that pinch, they squeeze back and literally lock up blades in the material and you have to cut them out with a torch. Going to an extra heavy set (.100” set) opens up a larger kerf so when the material squeezes back it won’t squeeze back enough to lock the blade up to into the material.
The most important thing, however, is to get the proper tooth pitch, which is how many teeth are in the blade per inch.
“That’s the whole name of the game,” Chibe says. “Usually when you’re looking at tooth pitch, that’s where you would take into consideration the cross section of the material you’re cutting. A lot of the saw blade manufacturers will have a tooth selection chart in their saw blade catalogues. What they’re trying to do is get you the right edge material and tooth pitch determined by the material cross section.”
There is a rule of thumb we use in band sawing: It’s called “Three. Six. Twelve. Twenty-Four.”
“Those four numbers tell you everything you need to know,” Chibe says explaining that, starting from the outsides, the number three, means you never want less than three teeth in the work at one time. The number 24 on the other end, means you never want more than 24 teeth in the work at one time.
“You never want all the cutting force to be less than three teeth or you’re going to be in trouble. That’s a lot of force and you’re probably going to snap a tip off. With 24 teeth in the work at one time or greater, you will be running out of gullet capacity. That gullet is going to be full before the tooth ever passes out of the work,” Chibe says. “The two middle numbers—six and twelve—that’s the optimum. That’s what we are shooting for, getting six to twelve teeth in the work at one time and you should be in pretty good shape. That’s the sweet spot.”
There is also the consideration of whether to go with a varied pitch or a straight raker pitch, which offers the same number of teeth per inch. Chibe says that he’s found through experience that a varied pitch (which would be like a 2-3, a 3-4, a 4-6, or a 5-8 pitched blade) is often the better approach.
“The number of teeth varies as you’re going through the blade. The reason for that is that it helps break up harmonic vibration. When you go with a straight raker pitch, you develop a harmonic wave which can lessen the life of your blade,” he cautions. “When you hear a blade squealing really loud, that’s harmonic problems that you’re having. Heat and vibration are the things that help destroy a bandsaw blade.”
5. Once you do settle on the right blade, what’s the best way to break it in so that blade life is maximized?
The best way is to do it is on a piece of solid, advises Gordon.
“When breaking in a blade, what we are trying to do is hone the teeth. When a blade is brand new from a manufacturer it has a very sharp point. Think of it as a sharpened pencil,” Gordon explains. “When you first sharpen a pencil, and you push on it, that tip will break off, but once in use it will round. It’s the same thing with the blade.”
Essentially what you will be trying to do is make the blade not work as hard as it would during production. This is how to go about it, Gordon advises: Keep blade speed the same for whatever material you’re cutting (you change your speed based on the type of material, not the size of it). Then reduce the feed pressure, so the blade is not working as hard.
“A lot of people make the mistake of backing everything off. Let’s say for the particular material being cut, you typically set it at 200 ft per minute and 100 lbs of pressure. In many cases people will take that 200 ft per minute and drop it to 100 ft per minute and drop the pressure to 50 lbs per minute. But then everything remains the same in terms of the percentages, so the blade is working at least as hard now, if not harder, because the blade speed is way off and that causes problems,” Gordon says.
Instead, keep the blade speed where you normally keep it for whatever material you’re cutting, back the pressure off, and perform 15-20 minutes of actual cutting.
“If you get in the habit of breaking in new blades, it will certainly increase your blade life significantly,” is Gordon’s last piece of sage advice. SMT
