last updated: 06/04/20
Rotation speed n in RPM:
This is the speed of the spindle in Revolutions Per Minute (RPM)!
Cutting speed vc in m/min:
Speed of a tool (cutter) when cutting normally in
m/min. The cutting speed depends on the material. Typical values range from
50 to 500 m/min. It is the speed of a rotating tooth! and we get it from tables. If needed it can be calculated with the diameter of the tool
d in mm and the spindle speed
n in RPM (Revolutions Per Minute):
vc = (d·π·n)/1000. With a maximum spindle speed of 20000 1/min we get:
vc = d·63 m/min. This shows, that we can get a higher speed rate by choosing a bigger diameter of our tool.
Feed rate (feed speed) vf in mm/min:
Tool’s distance travelled during one spindle revolution.
Diameter in mm:
Diameter of the tool (cutter).
Number of teeth:
Number of teeth (cutting edges, flutes) of the used tool (cutter).
Tooth feed fz in mm/tooth:
Also chip load (cpt: chip per tooth) is the amount of material, which should be removed by each tooth of the cutter as it rotates and advances into the work.
The rate of material removal, but also the power requirements and the finish quality of the surface are determined by the feed rate and the cutting speed. They are mostly determined by the material that’s being cut. Softer material need lower cutting speeds. Harder cutting tool material need higher cutting speeds.
First we need to calculate the rotation speed in RPM with the following formula (
n = rotation speed in RPM,
vc = cutting speed in m/min,
d = diameter in mm)
n = (vc·1000)/(π·d)
The cutting speed for e.g. wood is selected from a table.
|Material||Cutting speed in m/min|
|Hardwood and MDF||450|
|Brass, Bronze, Copper||360|
|Aluminium (wrought alloy)||300|
|Cast-Aluminium > 6 % Si||200|
We get 500 m/min. This gives us a speed for the cutter resp. our spindle of 500000/3.1415 = 159160 RPM (revolutions/min) if we use an 1 mm tool. Ok, here is a problem! The max. speed of my spindle is 20000 RPM! So we stay with 20000 RPM for the next formula to calculate the feed speed:
vf = n·z·fz
In the following table (sorotec.de) we find the tooth feed in mm/tooth for spiral toothed cutter (solid carbide, fishtail, upcut-spiral, 3,175mm (1/8")).
|Material||Tooth feed in mm/tooth for d (mm)||0.5||1||1.5||2||2.5||3|
|Brass, Bronze, Copper||0.003||0.004||0.006||0.008||0.012||0.015|
|Aluminium (wrought alloy)||0.003||0.004||0.006||0.008||0.012||0.016|
|Cast-Aluminium > 6 % Si||0.002||0.003||0.005||0.007||0.011||0.015|
The table gives only rough values! to be able to calculate the feed rates. Optimum feed rate will be determined from experience. A good approach is to start off with half of the calculated feed rate and gradually increased to the capacity of the machine and the finish desired.
With our 20000 RPM we get a feed rate of 20000·2·0.01 = 400 mm/min for a 1 mm cutter in wood or 1200 mm/min for a 3 mm cutter.
Here I will try to document settings that worked for me (spindle 3000-20000 RPM).
|Material||Cutter||Feed rate in mm/min|
|plywood birch 4 mm||spiral diamond 1 mm||400|