How Carbide Saw Blades Are Made
May 14, 2012 by Steve Maxwell
We all use carbide saw blades, but how they’re made was a mystery to me until last week. The afternoon I spent touring Irwin’s new manufacturing plant in Udine, Italy left me surprised and impressed. This place was designed and built by saw blade guru Giorgio Pozzo, and is the brightest, whitest, cleanest plant I’ve seen in my life. This one facility produces hundreds of thousands of circular saw blades each year, running three shifts of only 10 people each. Here in Canada we won’t see the Irwin Marples blades coming from the Udine facility until December, but this blog gives you a sneak peek, as well as my experiences seeing these blades used first hand.
There are distinct steps involved in making a carbide saw blade, and cutting out the blade body is the first of them. At the Irwin plant this operation happens with a laser. It’s used to cut sheets of German-made steel that are fed into the machine. The computer controlled laser cuts through alternating areas of the blank, minimizing heat build up in any one area. The design for blade bodies happens entirely on proprietary CAD software in the engineering office, then is transferred directly to the cutting machine. The design system is efficient enough that one engineer can create as many as 10 to 15 new blade designs every day.
After lasering out the blanks, the disks are heat treated to remove stresses in the metal. Stacks of blanks are sealed in a chamber for hours or days, heated up to 450ºF, then cooled at a controlled rate before moving on to the tensioning process.
Tensioning creates a slightly dished shape across the diameter of the blade, creating greater resistance to vibration during a cut. A steady blade is a smooth blade. As useful as internal tension is, the dished shape that created this tension is not good. That’s why blade bodies are ground flat after the dished shape has been made. You get the benefit of the internal tension, but with the essential flat blade shape.
In a plant like this one you’d think that all manufacturing would be automated, but there’s one crucial area where hand work and human judgement still matters. Balancing the blades happens when skilled machinists grind each blade by hand until it’s within specs. Typical 10” blades are balanced to within 1 gram across their diameter, while the Irwin blades I saw being made were balanced to within less than 0.5 grams. Each blade is measured for balance, then ground on a bench grinder and checked again.
Next comes the carbide teeth. They’re mechanically sorted and electrically brazed onto the blade body before being ground to shape in the enclosed cabinet of a computer controlled machine.
As interesting as all this is, the bottom line is a blade that cuts well. That’s all that really matters. If the performance of the Irwin Marples blades we’ll be getting matches what I saw from blades pulled out of production for testing in the analysis shop in Udine, we’re in for something very good. The 10” general purpose blades I saw cut everything from 2”-thick hardwood to 1/4” plywood completely smooth – both faces and edges. Even the bottom side of 3/4” melamine was crisp and entirely chip-free.