Technical SectionPhone: 516-328-3970www.technocnc.com9With fan-cooled systems, the duty cycle of the spindle is approximately 60% to 70%. Another is the noise generated by the arbor fans which tends to be in the upper70s to lower 80s decibel range; however, electric fan-cooled spindles do not have noise related issues. These spindle offerings usually do not exceed 24,000 rpm and are usually the most economical.Compressed-air-cooled spindles allow for a 90% dutycycle. These require a constant stream of clean non fluctuating source of compressed air. These spindles are typically used for greater then 24,000 rpm. These spindles usually incorporate ceramic bearings.This method is the most efficient and allows for duty cycles of 100%. These spindles are ideal for very demandingapplications such as production of very hard materials in a 24/7/365 day operation. The constant loads on the spindle generate a lot of heat, and the only method to remove this excess heat is through a separate liquid chiller unit. Choosing a SpindleThere are many spindle options available for Techno CNC Routers. Correct selection of a spindle is imperative for optimum machine performance. The electric spindle is the heart of the machine. Many variables must be considered when selecting the correct spindle such as material to be cut, production volume, tooling, machine feed rate, and spindle rpm. Generally, each material and cut has an ideal tool profile and cutting speed. Larger diameter tools require slower speeds. Smaller diameter tools require higher speeds.Spindle speed and feed rate for a given cut must be balancedfor best quality, tool life and spindle life. Incorrect spindle speed is a common error in CNC machining. Machine feed rate and spindle rpm are directly related to one another. The higher the rpm, the faster the machine must be cutting. The typical question is how fast should I be cutting? This can be determined by the chip load. Simple formulas can be used to predetermine feed rate.Many cutter manufacturers supply this information with the specific cutter to be used for different types of material to be cut. This will get you close and the optimal feed rate can be fi ne-tuned at the machine. Typically, feed rates that are too slow will decrease tool life due to the increased friction.This increasedfriction will not only wear out the cutter, but will also heat up or burnthe material being routed. Other considerations that must be taken is how to enter the part. Ramping into the part is the preferred method. The ideal ramp should be between 0 and 20 degrees from the table surface. This angle will allow you to enter into the material at 100% of the feed rate. At any angle greater then 20 degrees, the feed rate should be reduced accordingly. Entering into the part on a ramp will greatly increase spindle bearing and tool life. (chipload) x (# of cutting edges) x (rpm) = feed rateFormula:CNC ToolingCutting Tool GeometryThe tool geometry influences cut quality, cutting speed, chip removal, and the life expectancy of the tool in a specifi c material. Choosing the right tool for the specific material beingrouted can be critical. There are several different geometries to choose from such as upcut / downcut helix, straight fl ute, and ball nose, to name a few. The cutter selection of this catalog defines in more detail the ideal geometry for specifi c materials. Illustrations on the next page shows basic terms used to define a tools geometry.Router Bit MaterialsThere are four basic materials to choose from when selecting a router bit for a specific application: High-speed steel, carbide tipped, solid carbide and PCD diamond. The choice of a specific tool depends on the material being routed.High-speed steel and carbide tipped tools tend to be used more with hand held routers vs. CNC Routers. The steel bodyof the tools tends to withstand the vibration caused by the inconsistencies of hand feeding the router. Another reason they are used with hand routers is that they are available in many geometries for low cost, and available at most home centers. The ideal choice for a CNC Router is solid carbide or PCD Diamond. Solid carbide is the most common router bit used on CNCs. It provides long life due