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Technical Section Phone: 516-328-3970 www.technocnc.com  9 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 usuallythemosteconomical. Compressed-air-cooled spindles allow for a 90% duty cycle.   These   require   a constant  stream  of  clean  nonfluctuating  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 slowerspeeds. Smallerdiametertoolsrequirehigherspeeds. 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 fine- 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 specific 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  flute,  and  ball  nose,  to  name  a  few.  The  cutter selection  of  this  catalog  defines  in  more  detail  the  ideal geometry for specific 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