Examples on process control

Week 3: process control for CNC machines

February 16, 2012

1

Steps to determine coordinate system

• Rule: for programming coordinate system; the axes are defined from the spindle location NOT the operator’s location

• First: determine the Z axis (positive is away from workpiece and negative is into the workpiece

• Second: determine the long and short axis normal to the Z-plane

• The long axis will be the X-axis, the short will be y-axis

• Third: Use the right hand rule: start with the Z-axis pointing figures and then determine the remaining x and y axes; (thumb figure points to positive X-axis), index figure points to positive Y-axis)

2

3

4

Absolute and incremental coordinates

5

Mathematical considerations for CNC programming

• Compute the sides of right triangles

• Compute the angles of right triangles

• Computes the sides and angles of Oblique triangles

6

Right triangle

• One angle is 90⁰ , and longest side is called Hypotenuse

)(adjacent side

)( opposite side)tan(

)(adjacent side)cos(

)( opposite side)sin(

Hypotenuse

Hypotenuse

222

)tan(,

)cos(,

)sin(,

)tan(,

)cos(,

)sin(,

BAC

A

B

C

A

C

B

B

A

C

B

C

A

BB

BB

BB

AA

AA

AA

7

Angles

• Vertical angles are equal

• Alternate interior angles are equal

• 1 minute is equal to 1/60 of a degree

06

1 Minutesdegree

8

Examples

• Example: assume you are working on CNC machine with no rotary table, determine the coordinates that must be input for drilling hole 2 from the absolute origin (X0,Y0)

9

Determine the location of each drill hole using both dimensioning systems

10

Oblique Triangle

• Three sided figure but none is 90⁰

)cos(2

)cos(2

)cos(2

)sin()sin()sin(

222

222

222

c

B

A

CBA

abbac

accab

bccba

CBA

11

Tool feed for hole operations

• Feed is the rate at which tool advances in the work per revolution (ipr)

• Tool feed rate: is the distance (feed) the tool moves per minute

– Tool feed rate (ipm) = feed (ipr) x spindle speed (rpm)

– Tool feed rate (mpm)= s (mmpr) x rpm

– Tool cutting speed = π x tool diameter * RPM/12

• Tool feed rate is value entered into CNC machine

12

(mm)Diameter Tool

(mmpm) Speed Cutting Tool*1000*31.318RPM

units

Diameter Tool

Speed Cutting Tool*4RPM Spindle

412

but

12

Diameter Tool * Speed Cutting

Spindle

Metric

Tool

12

* ertooldiametferencetoolCircum

13

Example

• Determine the feed rate for taping tool having 18 threads per inch and spindle rotating at speed of 300 rpm

14