Driling, Countersinking and Counterboring - Course: Technique for Manual Working of Materials. Trainees' Handbook of Lessons
 (introduction...) 1. Purpose of drilling 2. Machines for drilling 3. Tools for metal drilling 4. The operation of drilling 5. Setting of the tools 6. Clamping of the tools 7. Clamping of the workpieces 8. Technological process of drilling 9. Purpose and application of counterboring/countersinking 10. Labour safety recommendations

### 5. Setting of the tools

At bench-type and upright drilling machines, the ‘rotational speed’ and - with modern types - the ‘cutting speed’ and ‘feed’ must be set.

The rates of ‘rotational speed’, ‘cutting speed’ and ‘feed’ depend on the material to be drilled and the diameter of the drill.

To automatic feeds the following rules apply:

Low feed rate - with high rotational speed and hard material
High feed rate - with low rotational speed and soft material

The automatic feed is not required for making smaller bore holes (up to 12 mm dia.)

The cutting speed for drilling without automatic feed can be fixed at 22 m/min. Thus, the following rotational speeds apply:

 Materials Diameter of the drill in mm (Range) 1 - 3 3 - 5 5 - 8 8 - 10 10 - 12 12 - 16 Soft materials (aluminium, copper) 7100to4500 5600to3500 3500to2200 2800to1800 2200to1400 1800to1100 Medium hard steels cast steel 2800to1800 2200to1400 1400to900 1100to700 900to560 710to450 hard materials (chromium-nickel alloys) 350 350 350 350 280 220

The following rule applies to the setting of the rotational speed:

Low rotational speed - with hard materials and great drill diameters
High rotational speed - with soft materials and small drill diameters

The rotational speed can be calculated with the help of the following formula:

n = rotational speed (in r.p.m.)
v = cutting speed (in m/min)
d = diameter of the rotating piece (in mm)
p = 3.14

Calculating example

What rotational speed has to be set if a bore hole of 10 mm shall be drilled into a workplace of steel on a bench-type drilling machine with feed by hand?

Exercise

What rotational speed has to be set if a bore hole of 5 mm dia. shall be drilled into a workpiece of steel by a bench-type drilling machine with hand feed?
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Compare the result with the value of the table:

 Calculated value Value indicated in the table