Abstract
Rapid prototyping is widely used to reduce time to market in product design and development. Today's systems are used by engineers to better understand and communicate their product designs as well as to make rapid tooling to manufacture those products. Computer Numerically Controlled (CNC) milling machines are part of this technology. This project will present the design of a small CNC machine, and production, and analysis of a small CNC machine. This machine has the characteristics demanded by the industrial and academic designers. Studying the
existing machines aided in setting specifications for the new design. Comparing the performance of the new machine with existing machines will improve future designs.

Table of Contents
1 Chapter 1 - Introduction & Problem Solution 1

11 Solution Methodology 2

2 Chapter 2 - Performance Metrics of Numerically Controlled Machines 4

1 21 Geometrical Errors 4
211 Backlash 9
212 Scaling Mismatch 10
213 Squareness Error 12
214 Cyclic Error 13
215 Lateral Play 15
216 Reversal Spikes 16
1 217 Stick Slip 18
218 Vibration 19
219 Master-Slave Changeover 20
2110 Straightness 22
2111 ASME Standard Test Method 23

3 Chapter 3 - Performance Evaluation of Existing Machine 25

31 Discussion o f Measurements of Microkinetics Performance 26
32 Discussion o f Measurements of Prolight Performance 31

4 Chapter 4 - Design Specifications for the New Machine 36
5 Chapter 5 - Design of the New Machine 39

51 The Hardware 40
511 The Structure 40
512 X & Y Axis 41
5121 Axis Motor 43
5122 Axis Actuator Hardware 45
5123 Rolling Contact Bearing 48
5124 Motor Mounting 54
5125 Linear Slides 56
513 Z Axis 61
52 The Software
53 Driver and Electronics

6 Chapter 6 - Measurement of Performance of the New Mill
7 Chapter 7 - Discussion of Results
8 Chapter 8 - Recommendation for Future Work

Appendices
A G & M Codes
B Calculation Sheet for the Ball Screw
C Important PartsofEMCINI File
D Diagram ofThe Driver’s Circuit
E  Calculation and Selection o f the Stepper Motor
F Engineering Drawings of GVSU Mill
References

Table of Figures
Figure 211 the hardware required for the Renishaw ballbar test 5
Figure 212 feed in, out, angular overshoot arcs and the data capture arcs 6
Figure 213 the data capture range of the ballhar transducer is approximately 2mm 7
Figure 214 a plot o f time vs transducer travel shows the period of machine
acceleration and how it would affect the integrity o f the data collected 7
Figure 2111 an example of positive backlash 9
Figure 2112 the interpolation of the inward step in the ball bar plot 10
Figure 2121 an example of a scaling mismatch error 11
Figure 2131 positive and negative squareness 13
Figure 2141 an example of cyclic error 14
Figure 2151 an example of a lateral play in the y axis 15
Figure 2161 an example plot of a reversal spikes error 16
Figure 2162 an example o f the effect of a reversal spikes error on the actual circle milled on the part 17
Figure 2171 stick-slip error as shown on a diagnostic problem 18
Figure 2172 the effect of stick-slip on the machined part 19
Figure 2181 a typical plot showing vibration error 20
Figure 2191 a master-slave changeover error as captured by the ball bar diagnostic plot  21
Figure 2192 master slave changeover every 45" 21
Figure 21101 three distinct distortions in the plot caused by an error in the y axis straightness 22
Figure 311 a plot of the ballbar test on the Microkinetics CNC express 27
Figure 312 representation of the angular error and how it can cause a scaling mismatch error 29
Figure 320 diagnostic plot of the proLIGHT on the same scale as the Microkinetics 32
Figure 321 a plot of the ballbar test on the proLIGHT CNC machining center 32
Figure 322 duplex arrangement angular contact bearings 34
Figure 5 a solid model of GVSU mill 39
Figure 5111 the structure of GVSU mill 40
Figure 5121 the X, y axis including the linear slides 41
Figure 5121 the axis drive system 42
Figure 51221 lead screw and nut 45
Figure 51222 ball screw and nut 46
Figure 51231 deep groove ball bearing 48
Figure 51232 the driver and the follower pulley diameters and distance 51
Figure 51241 timing belt, and timing pulleys 54
Figure 51251 illustration of the dovetail slides 56
Figure 51252 illustration of the linear ball bearing slides 57
Figure 51253 illustration of the crossed roller bearing slides 58
Figure 51254 the guided linear sliding system 59
Figure 5131 the spindle assembly 61
Figure 531 the drive rack and the G201A inside 66
Figure 61 the first diagnostic plot of the new machine using a 50 mm ballbar 69
Figure 62-1 diagnostic plot of the second test on a 100 pm plot scale as the first test72
Figure 62-2 diagnostic plot of the second test on a 50 pm plot scale 72
Figure 63 diagnostic plot of the final test 74
Figure 71 percent deviation from the compromised performance values 79
Figure 81 self aligning linear bearing may cause unwanted movement of the axis 82


List of Symbols and Abbreviations
CNC Computer Numerical Control
mm millimeter
m meter
pm micro meter
9 theta, the value quoted for squareness by the diagnostic software
Dy the wavelength of the cyclic sinusoidal error
ASME American Society of Mechanical Engineers
CW Clockwise
CCW Counter-Clockwise
ISO International Organization for Standardization
JIS Japanese Industrial Standard
ozin ounce per inch
RPM Revolution Per Minute
VAC Volts of Alternating Current
Ibf pounds of force
lb pounds of weight
Deg degree
CMM Coordinate Measuring Machine
DC Direct Current
Fa axial force
L lead of a ball screw (inches)
T torque
e efficiency
n pi(p belt inclination angle
C distance between centers of pulleys
Ri radius of the motor pulley
Ri radius of the screw pulley rad radians
F  B m a x the maximum radial force
a angle of warp of smaller pulleycoefficient of friction between pulley
HP Horse Power
AFBMA Anti Friction Bearing Manufacturers Association
P equivalent load
Fr applied constant radial load
V rotation factor
X radial factor
Y thrust factor
L fatigue life expressed in millions of revolutions
C the basic dynamic load rating
NC Numerical Control
CAD Computer Aided Design
CAM Computer Aided Manufacturing
DOS Disk Operating System
PCI Peripheral Component Interconnect
EMC Enhanced Machine Controller
API Application Programming Interface
NIST National Institute of Standards and Technology
GUI Graphical User Interface
MDI Machine Device Interface
PC Personal Computer
TIL Transistor - Transistor Logic