Machinery Design
EGTE 435
Spring, 2007

Manufacturing Project
Supplemental Material

Table of Contents for this Page


Assembly and Fastening Options

The only requirement for your design in terms of assembly and/or fastening is that you cannot use adhesives or press fits!.  The Machine Shop has an inventory of fasteners and other hardware including:

Drawing Requirements

Drawings are required for all work in the machine shop.  You must generate a drawing for each component you are fabricating as well as an assembly drawing.   Each drawing must have a standard title block and must be signed by Dr. Glancey or Dr. Keefe before you start working in the shop.

When working in the shop, any injury or any cut that draws blood must be reported to the shop personnel. Before returning to work, you must go to the "Student Health Center" (Infirmary) and fill out an accident report.

Acceptable Part Features for this Project

* - Drills, taps, reamers, end mills, tool bits and other tooling limited to what is available in the student shop,  See Art for current inventory.
Other Suggestions:
1.    If milling down the thickness of large pieces of plate stock, keep the thickness at least 0.37".
2.    In general, the lengths of round pins should be no greater than twice the diameter.
3.    For grooves, keep the width at least 0.13" and the minimum diameter at least 0.37".
4.    Clearances for slip fits should be at least 0.001".
5.    Make sure tolerances are appropriate for the design; be sure to account for cumulative errors!
                  Note:  You are encouraged to discuss any questions you may have as well as exceptions to the above list with Art
                                prior to submitting your drawings.

Tolerances and Surface Finish

Tolerances and surface finish play a key role in any design.  A majority of the time the two go hand in hand.  Close tolerance specifications often time require a machining method that results in a higher quality surface finish.  They play a role in the function, operation, assembly and overall appearance of a design.  In order to obtain finer surface finishes and closer tolerances there needs to be better control of the machining parameter.  The initial quality of new equipment, and wear in older equipment can also have an effect on achieving the needed surface finish and tolerance.  The figure below shows tolerance capacity of various processes.  Typically, saw cutting is assumed to provide a tolerance ranging from 1/16" to 1/32".  
    Figure 1.  Tolerance capability of various processes.  Source: S. Kalpakjian, Manufacturing Engineering and Technology, 3rd ed. Addison-Wesley, 1995
A few key things to keep in mind are that closer the tolerances and the finer the surface finish, the higher the cost and time to produce become.  Figures 2 gives a general idea towards how this tolerance versus cost trend behaves, while Figure 3 shows the typical surface roughness attributed to various machining operations.  
Figure 2. Relationship between relative machining cost and tolerance. Source: S. Kalpakjian, Manufacturing Engineering and Technology, 3rd ed. Addison-Wesley, 1995     Figure 3.  Range of surface roughness obtained in various machining processes. Source: S. Kalpakjian, Manufacturing Engineering and Technology, 3rd ed. Addison-Wesley, 1995.