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Technical Section Phone: 516-328-3970 www.technocnc.com 9 With  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 upper 70’s  to  lower  80’s  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% duty cycle. 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 demanding applications 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 Spindle There  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 balanced for 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 increased friction will not only wear out the cutter, but will also heat up or burn the 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 rate Formula: CNC Tooling Cutting Tool Geometry The 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 being routed 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 tool’s geometry. Router Bit Materials There  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 body of 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 CNC’s. It provides long life due