This document discusses the basics of CNC machines including leadscrews, basic length units (BLU), and converting rotational motor motion to linear motion using pitch and teeth per inch. It provides an example of calculating pulse rate and count given a machine's BLU, feed rate, and distance to move. Open and closed loop controls are mentioned along with advantages of CNC like easier programming, storage, changes, avoiding errors, and producing complex geometries as cheaply as simple ones.

1. BLU
BASIC LENGTH UNIT

3. LEADSCREWS
Leadscrew
Pitch
Nut
Converting the rotational motion of the motors to a linear motion.
pitch (p): the distance between adjacent screw threads
The number of teeth per inch (n):
n = 1 / p
BLU: Basic Length Unit (machine resolution)
BLU = p / N

4. Example
A machine has 1 BLU = 0.001".To move the table 5"
on X axis at a speed (feed rate) of 6 ipm. Calculate
pulse rate and pulse count.
• pulse rate = speed/BLU = 6 /0.001
• = 6,000 pulse/min
• pulse count = distance/BLU

6. Open Loop vs. Closed Loop controls

7. Advantages of CNC
- Easier to program;
- Easy storage of existing programs;
- Easy to change a program
- Avoids human errors
- NC machines are safer to operate
- Complex geometry is produced as cheaply as simple ones
- Usually generates closer tolerances than manual machines