Spindle Speed
Using the correct spindle speed is important for safe and satisfactory results, as well as maximiz- ing tool life.
To set the spindle speed for your operation, you will need to: (1) Determine the best spindle speed for the cutting task, and (2) configure the mill con- trols to match the closest spindle speed.
Determining Spindle Speed
Many variables affect the optimum spindle speed to use for any given operation, but the two most important are the recommended cutting speed for the workpiece material and the diameter of the cutting tool, as noted in Figure 26:
*Recommended
Cutting Speed (FPM) x 12
= RPM
Tool Diameter (in inches) x 3.14
*Double if using carbide cutting tool
Figure 26. Spindle speed formula for milling.
Cutting speed, typically defined in feet per minute (FPM), is the speed at which the edge of a tool moves across the material surface.
A recommended cutting speed is an ideal speed for cutting a type of material in order to produce the desired finish and optimize tool life.
The books Machinery’s Handbook or Machine Shop Practice, and some internet sites, pro- vide excellent recommendations for which cutting speeds to use when calculating the spindle speed. These sources also provide a wealth of additional information about the variables that affect cutting speed and they are a good educational resource.
Also, there are a large number of easy-to-use spindle speed calculators that can be found on the internet. These sources will help you take into account all applicable variables to determine the best spindle speed for the operation.
The procedures for setting the spindle speed for the Models G0747 and Model G0748 differ. Use the appropriate section on the following pages for your mill when selecting the speed range.
To avoid damaging the spindle, gears, or cutting tools when setting the spindle speed range:
•Spindle rotation must be turned OFF and the spindle must be at a complete stop BEFORE you change the spindle speed range.
•To avoid damaging the moving parts inside the headstock, never start spindle rotation without the range selector detent pin firmly seated in either the high or low position.
•When the spindle speed range is changed, the spindle rotation direction reverses. You will need to either change the cutting tool to match the direction of spindle rota- tion or use the spindle direction switch to compensate for the reversal.
Model G0747/G0748 (Mfg. Since 8/12)