Home Page
8   Phone: 516-328-3970 www.technocnc.com  Technical Section operator intervention while the manual quick change system usually requires the operator to activate a signal to release the tool and to activate another button to reload the next tool into the spindle. The  question  of  which  spindle  should  be  selected depends  primarily  on  the  applications  and  quantities  of parts to be made. The benefit of the automatic tool change system is that a great deal of time can be saved for parts that are to be made in large quantities that also require a number of  different  tools.  If  the  quantities  are  not  so  large,  the manual  quick  change  might  represent  an  economical compromise. In the case where the quantities of the parts are small or only a small number of tools are required, there is no clear benefit to using either a quick change or automatic tool change system. Tool Length Offset The  main  difficulty  with changing tools on spindles is adjusting the length of the new tool to match the previous tool so   that   the   software   can continue at the correct height of machining. This task is no longer very time consuming. In the  past,  the  operator  would have to either carefully adjust the tool height relative to the workpiece  with  gauge  blocks or adjust the height of the Z-axis relative to the work-piece to re-zero the Z-axis. Although this is not difficult, the task had to be performed carefully or else the second tool would not be at the correct height and the part might have a visible defect. Now, all Techno machines and many other CNC machines come with tool-length sensors and compensation software.  This  allows  for  the  tool  length  to  not  only  be measured  but  automatically  compensated  for  in  the  G- Code software, with a simple and automatic process. Spindle Power The traditional way that the spindle power is “measured” is by the HP rating. This rating has to be carefully considered since the HP rating is generally proportional to the spindle rpm. For example, if a 3HP spindle is rated at 3HP at 18,000 rpm, it would only have 2HP at 12,000 rpm. The speed at which the rating is specified is therefore extremely important. The  other  aspect  of  spindle  power  that  must  be considered is the nature of the power rating. The power rating on the brush type spindles is generally specified as a momentary peak rather than a continuous rating. The rating for AC spindle motors is usually considered a continuous rating but even this might be specified as a function of duty cycle. Some spindles are rated for 100% duty cycle – able to maintain the rated power continuously, while others are rated for a 60% or 80% duty cycle. In the latter case, the expectation is that the spindle will be used to its rated power for a few minutes and then allowed to “rest” for a brief period before the next part. This duty cycle rating is associated with the required cooling of the spindle. Spindle Cooling Three common methods of spindle cooling include: fan, compressed air or liquid. There are two types of fan-cooled spindles. First is an electric fan which will blow air through the spindle body. The second is a fan blade attached to the spindle  arbor.  This  method  of  air  flow  is  dependent  on spindle  rpm.  Both  methods  of  cooling  have  drawbacks. With fan-cooled systems, the duty cycle of the spindle is Brushes Noise Service Required Speed Control Power Range Tool Change Option Cost TIR Accuracy Voltage Required Current Used for 3HP Maximum Collet size Features Yes Noisy due to the brushes Brushes need to be replaced regularly Minimal, not precise, usually manual if available Typically in the 0-3 HP peak range Manual < $1,000 dollars Usually in the .002" - .004" range 120V AC typical, 220V AC single phase available For 3HP peak – 15A circuit required .5" typical None Relatively Quiet None - Bearings are usually sealed and lubricated Usually adjustable from the AC inverter that is needed Fractional HP to 20HP and above Manual or Automatic Thousands of $ Usually < .002" 220-440V AC, single or 3 phase 220V AC single phase – 16A 220V AC 3 phase – 10A 1.5" and higher Brush Spindle AC Spindle