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moldmakingtechnology.com 41 a 1-inch-wide slot. Trying to use a ½-inch-wide tool to create a ½-inch-wide slot would create too much surface contact, and the tool would fail immediately. A good rule of thumb is to use a tool about half the size of the tightest area. In this example, the tightest area is the 1-inch slot, so the ½-inch- diameter tool is the largest tool that should be used. When the tool radius is smaller than the tightest area of the part, there is room for the tool to move around, and the engage- ment angle is minimized. This means a tool with more cut- ting edges and faster feed rates can be used. Machine rigidity also helps dictate the size of the cutter that can be used. In 40-taper machines, for example, the diameter of the tool is typically less than ½ inch. Larger- diameter tools generate more force than the machine can handle, resulting in chatter, deflection, poor finish and decreased tool life. In addition, when the tool is half the size of the tightest area, the angle of engagement can stay low and not increase. For example, if you program a part with a 10-percent stepover, the angle of engage- ment is 37 degrees. With older, tradi- tional tool paths, this engagement angle would increase to 127 degrees every time the tool changes direction. In newer, high-speed tools paths, the tool literally "sounds" the same in corners as it does in straight-line cuts. Sound is a good way to check on the optimization of the tool paths. A tool that sounds the same dur- ing all the cutting is not experiencing spikes in heat and shock. If the tool squeals every time it changes direction or hits a corner, it is an indi- cation that you may want to decrease the cutter diameter of the tool to reduce the engagement angle. When the cut sound is consistent, the tool is experiencing constant pressures that are not fluctuating as the part geometry varies. This is because the angle of engagement remains constant. The Deluxe Company Serving the Steel Industry for Over 65 Years 99 Berry Road • Washington, PA 15301 Phone: 724.222.2100 • Toll-Free: 800.537.7528 Fax: 724.225.1868 Machinability Made Easier Marshalloy MQ/FM Mold Steel Q / ® Learn more at www.MarshalloyMQFM.com The quality of molds depends on the material you use. With Marshalloy MQ ® /FM , you get pre-hardened alloy steel plate that give your molds the consistency they need to deliver optimal performance. This mold quality, free machining steel is made with a proprietary melting and refning process, resulting in superior: • Machinability • Uniformity • Hardness • Cleanliness • Tensile Strength • Polishability Marshalloy MQ ® /FM is decarb-free and stress-relieved, making it ideal for EDM processes. To produce parts that meet specifcations time and again, use Marshalloy MQ ® /FM. Toroidal tools like these are appropriate for machining tight areas.