Determining The Correct Spindle Speed; Determining The Spindle Speeds - Proxxon PD 400 CNC-ready Commissioning Manual

8.6. Determining the correct spindle speed

The cutting speed is a decisive parameter during machining. Too high or too low cutting
speeds affect the good end result, so the choice of spindle speed – which is decisive
for the cutting speed – is very important for a good surface and clean metal removal.
Another determining factor is the diameter of the work piece: the greater it is, the
greater the relative speed is at the circumference at constant speed. The relation is
characterised by the following equation:
whereby:
n: Rotational speed
Vc: Cutting speed
D: Diameter
The table on the gear case of the machine offers help in choosing the right cutting
speed. For known cutting speed "Vc" and known work piece diameter "D", the
necessary spindle speed "n" can be calculated.
An example:
An aluminium work piece with a 30mm diameter will be machined. The necessary
cutting speed according to the table is 100–180m/min. We will calculate 132m/min.
n = 132 x 1000/ (30 x 3.14) = 1400 rev/min
This result can be read directly in the table on the gear case.

8.7. Determining the spindle speeds

By combining the speed step switch pos. 23 (Fig. 1) and the position of the belt in the
machine's gear box, six main spindle speeds from 80 to 2800 rpm can be selected:
The specifications refer in each case to position I and II of the speed step switch.
14
n = Vc * 1000/ (D * 3.14)