The right cutting speed for drilling
The correct cutting speed is important to achieve good work results and minimize tool wear. The best way to understand the cutting speed is to draw a large circle on a sheet of paper. Now move your index finger along the line of the circle. You are now travelling a certain distance in a certain time. This is the cutting speed. It is determined by the diameter of the drill and the speed of the drill. Certain materials require certain cutting speeds. The cutting data is determined by the manufacturers of the tools. Let’s take a look at them:
The cutting speed is given in meters per minute (m/min). It depends on the material (e.g. mild steel) being machined, the material of the cutting tool (HSS or HM) and the type of process (drilling/wheeling/tapping).
The manufacturers of the tools make specifications regarding the cutting speed for different materials. The materials can be roughly divided into steel, stainless steel (VA), cast iron
and NOT ferrous metals.
Important: Also check if the materials are already hardened, usually you know the material and the size of the drill. Now you have to find out which speed to set on the drill. The mathematicians among you can calculate this with a formula . The formula for the cutting speed (m/min) is
3.14 times diameter( mm) times rotational speed ( 1/min ) x 1m/1000mm)
Now it’s up to the mathematicians. They solve the formula according to the value for the rotational speed, because that is what interests us:
RPM = cutting speed x 1000 divided by diameter x 3.14
Now we could use the cutting speed and the diameter of the drill and we would have the rotational speed as a result.
Calculation example for the cutting speed during drilling
Example: we drill an 8 mm hole in unalloyed tool steel. Cutting speed is 25 m/ min. (25 m/min) x1000 divided by 8 x 3.14 = 995 rpm.
Don’t worry: you don’t have to calculate every time. There are tables to look up. Then you can save yourself this calculation and read off the values you need directly there. If you have understood the basic principle, you will find the following tables wonderfully easy to use.
Technical table: cutting speed, rpm and diameter
Rotational speed = Cutting Speed x 1000 / Diameter x 3,14
n = v x 1000 / d x π = rpm ( revolutions per minute)