SHOP: Blade teeth are available in several shapes and settings, which can be 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?
GORDON: Looking at bimetal blades, the good news is that most of the manufacturers, Starrett included, will point you in the right direction. For example, let’s say you wanted an 18-tooth blade, typically you will get a regular set blade or a wavy set blade. A wavy set blade is for very thin material.. As you get coarser with regards to tooth shape, options become more limited. Most of the production bands are going to be positive rake from the majority of manufacturers. Most general-purpose blades will be 0 to a 3 or 4-degree positive rake, something that takes abuse better. The advantage of a positive rake is that it’s going to cut faster because it’s more aggressive. The disadvantage of a positive rake is that it’s not going to take abuse as well as your standard general-purpose blade. Knowing what you want to do with it is an important part of the equation. The shop cutting a wide range of shapes and materials, rather than hundreds of pieces of the same material, can use a general-purpose blade, which will take the abuse from cutting through different materials and shapes better than a full-on production positive rake. For example, if a shop is cutting four-inch rounds of stainless steel all day, then a production oriented blade is a good choice for productivity and value.
The most important thing with regards to the teeth, is the number of teeth in the material. Too many or too few teeth will cause a problem. That’s where the operator that cuts a little bit of everything can run into issues, if choosing a middle ground for the number of teeth The bottom line is no fewer than three teeth per inch in the material at all times. There are a lot of caveats with that, but it gets you in the ballpark. For example, if you have a one-inch piece of aluminum and put three teeth into it, it’s going to blast through it without any issues whatsoever. However, if that same one-inch piece of material is Inconel, a three-tooth blade will likely have teeth break off because they won’t have the chance to penetrate fully. The three teeth per inch is a standard number for everything under the sun, but it has to be understood there are exceptions to every rule.
Too many teeth will cause a problem as well. So, let’s say you are cutting two-inch Inconel with a 10/14, it will cut it, but it will be a very slow process. If you’re cutting two-inch aluminum with 10/14 the teeth will rip off, due to the gullets and teeth loading up with material. All cutting tools are basically the same, it’s a load issue that requires attention. There is a chip load on each tooth and you have to have the gullet capacity and the ability of the tooth to penetrate, fill up that gullet and evacuate the chips. In general, 24 teeth per inch is the maximum. On average, we might shoot for the 10-12 range, but it depends on the material. With aluminum you can get away with a coarse blade, because it’s so soft there won’t be issues with penetration. On the other end of the spectrum, Inconel is so hard that there should be more cutters engaged. You will not have issues with filling up the gullet because it does not pull a big chip. The biggest concern is the customer trying to cut a wide range of materials with one blade, and trying to come up with a middle ground for tooth pitch. The trick is to consider the material you are cutting the most and get yourself in the ballpark.
Jay K Gordon is the North America sales manager, saws and hand tools, for The L.S. Starrett Company.