The Design of a CNC Mill for Product Prototyping

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

1.1 Solution Methodology 2

2 Chapter 2 - Performance Metrics of Numerically Controlled Machines 4

1 2.1 Geometrical Errors 4
2.1.1 Backlash 9
2.1.2 Scaling Mismatch 10
2.1.3 Squareness Error 12
2.1.4 Cyclic Error 13
2.1.5 Lateral Play 15
2.1.6 Reversal Spikes 16
1 2.1.7 Stick Slip 18
2.1.8 Vibration 19
2.1.9 Master-Slave Changeover 20
2.1.10 Straightness 22
2.1.11 ASME Standard Test Method 23

3 Chapter 3 - Performance Evaluation of Existing Machine 25

3.1 Discussion o f Measurements of Microkinetics Performance 26
3.2 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

5.1 The Hardware 40
5.1.1 The Structure 40
5.1.2 X & Y Axis 41
5.1.2.1 Axis Motor 43
5.1.2.2 Axis Actuator Hardware 45
5.1.2.3 Rolling Contact Bearing 48
5.1.2.4 Motor Mounting 54
5.1.2.5 Linear Slides 56
5.1.3 Z Axis 61
5.2 The Software
5.3 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 PartsofEMC.INI File
D. Diagram ofThe Driverâ€s Circuit
E.  Calculation and Selection o f the Stepper Motor
F. Engineering Drawings of GVSU Mill
References

Table of Figures
Figure 2.1.1 the hardware required for the Renishaw ballbar test. 5
Figure 2.1.2 feed in, out, angular overshoot arcs and the data capture arcs. 6
Figure 2.1.3 the data capture range of the ballhar transducer is approximately 2mm. 7
Figure 2.1.4 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 2.1.1.1 an example of positive backlash. 9
Figure 2.1.1.2 the interpolation of the inward step in the ball bar plot. 10
Figure 2.1.2.1 an example of a scaling mismatch error. 11
Figure 2.1.3.1 positive and negative squareness. 13
Figure 2.1.4.1 an example of cyclic error. 14
Figure 2.1.5.1 an example of a lateral play in the y axis. 15
Figure 2.1.6.1 an example plot of a reversal spikes error. 16
Figure 2.1.6.2 an example o f the effect of a reversal spikes error on the actual circle milled on the part.