krarunit41

7/27/2019 KrarUnit41

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41-2

Objectives

Calculate the revolutions per minute

(r/min) for inch and metric size drills

Select the feed to be used for variousoperations

Calculate the revolutions per minute for

the reaming operation


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Cutting Speeds and Feeds

Two important factors

Diameter and material of cutting tool

Type of material being cut

Speed of twist drill referred to as cutting

speed, surface speed or peripheral speed

Distance point on circumference of drill will

travel in 1 min


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Recommended Cutting Speeds

Portion of Table 41.1 from text

Drill Size Cutting Speeds in Feet per Min or Meters per Min

in mm 40 ft/min 12 m/min 60 ft/min 18 m/min

1/16 2 2445 1910 3665 2865

1/8 3 1220 1275 1835 1910

3/16 4 815 955 1220 1430

Steel Casting Tool Steel

For every job, choose the drill speed that will

result in the best production rates!


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Economical Drilling Speed

Variables Type and hardness of material

Diameter and material of drill

Depth of hole

Type and condition of drill press

Efficiency of cutting fluid employed Accuracy and quality of hole required

Rigidity of work setup

Most important!


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Revolutions per Minute

Compute correct number of r/min of drill

press spindle for given size drill

Type of material to be drilled

Recommended cutting speed of material

Type of material from which drill is made


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Formula (Inch)

inches)inncecircumfere(drill

12minute)perfeet(min/

D

xCSr

Revolution per minute = number of revolutions

of the drill necessary to attain proper cutting

speed for metal being machined.

where CS = recommended cutting speed in

feet per minute for the material being drilled

D = diameter of drill being used


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Simplified Formula

Since not all machines can be set to exact calculated

speed, pi () divided into 12 to simplify formula

D

CSr

4xmin/

Example: Calculate r/min required to drill a in hole

in cast iron (CS 80) with a high-speed steel drill.

6402/1

320

2/1

4x80min/ r


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Formula (Metric)

)(

)(min/

mmD

mCSr

Convert so all units are in mm

D

CSr

1000xmin/

D

CSr

320xmin/

Example: Calculate r/min required to drill 15 mm hole in

tool steel (CS 18) using a high-speed steel drill.

38415

5760

15

320x18min/ r


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Feed

Distance drill advances into work for each

revolution

May be expressed in decimals, fractions ofan inch, or millimeters

Three factors govern rate of feed

Diameter of drill

Material of workpiece

Condition of drilling machine


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Drill Feeds

Table 41.2 Drill feeds

Drill Size Feed per Revolution

in. mm in. mm

18 and smaller 3 and smaller .001 to .002 0.02 to 0.0

18 to 3 to 6 .002 to .004 0.05 to 0.1

to 6 to 13 .004 to .007 0.1 to 0.18

to 1 13 to 25 .007 to .015 0.181 to 1 25 to 38 .015 to .025 0.38 to 0.6

Generalpurpose Work


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Drill Feeds

General rule: feed rate increases as drill sizeincreases

Too coarse

chip cutting edges

Too lightchattering noise, dulls cutting edge

Hard steels or alloys use slower feed

Softer metals drilled with faster feed

Blue steel chips indicate too much heat atcutting edge

Dull cutting edge or too high speed


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Cutting Fluids

Provide both cooling and lubrication

Properties of an effective liquid in

dissipating heatAble to absorb heat rapidly

Have good resistance to evaporation

Have high thermal conductivity

Oil: good lubricant, poor coolant

Water: best coolant, no lubricating value (promotes rust)


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Good Cutting Fluid

Cool workpiece and tool

Reduce friction

Improve cutting action

Protect work against rusting

Provide antiweld properties Wash away chips

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