Browse Prior Art Database

Low-Cost Accurate Chassis Assembly

IP.com Disclosure Number: IPCOM000120631D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 161K

Publishing Venue

IBM

Related People

Howell, SE: AUTHOR [+4]

Abstract

This article describes a chassis assembly for a personal computer (PC) that locates many subassemblies accurately without additional pieces which build up tolerances.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Low-Cost Accurate Chassis Assembly

      This article describes a chassis assembly for a personal
computer (PC) that locates many subassemblies accurately without
additional pieces which build up tolerances.

      Sheet metal, while still flat, can be punched with holes and
profiles blanked very accurately.  It is only when it is formed, or
bent around corners, that it loses its accuracy.  This is due
primarily to the variations in material runs, i.e., thickness,
hardness, composition, etc. In order to compensate for these
variations, the design disclosed herein utilizes the accuracy of the
flat pattern to locate features and control the tolerance build-up
around bends.  The holes and extruded features that are put in the
chassis while it is still flat are used to locate the various
subassemblies.

      Fig. 1 is a perspective view of the chassis of this disclosure.
It is seen that the various mounting features on the bottom surface
of the chassis are in the same plane, so that there is little
tolerance to accumulate.  Extruded pads A provide an accurate
three-dimensional feature to mount a main circuit board to the
chassis.  Critical to the circuit board location is the mounting of
the lower direct access storage device (DASD) support.  The DASDs are
plugged directly to the circuit board so there is little room for
positional variation.  Because they are all accurately positioned in
the flat, lower DASD support locating holes B are positioned to not
require adjustment at assembly.  Two extruded pockets C provide
additional strength, but not location.  This also applies for card
guide/support location and mounting.  Position to the circuit board
is critical, so that mounting holes D are held to close tolerances in
the flat.  This is important as the high insertion and extraction
forces of the PC processor card must be overcome.  Extruded locator
pads F for the feet U (Fig. 2) also are held accurately so that the
entire system can be positioned on a manufacturing pallet. They are
extruded downward so that the clearance required for the mushroom
head of the rubber feet is reduced.  A pierced and extruded locator G
will later be used to locate and fasten the upper DASD support.  Four
holes H can be used to locat...