Shadowgraph system projects magnified image on screen so that alignment of small electrodes mounted on electrical discharge machines can be corrected and verified. Technique may be adapted to other machine tool equipment where physical contact cannot be made during inspection and access to tool limits conventional runout checking procedures

Boissevain, A. G.

Nelson, B. W.

English

NASA Technical Reports Server

1972	 B72-10036 
NASA TECH BRIEF 
Ames Research Center	 4r 
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commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Optical Alignment of Electrodes on

Electrical Discharge Machines 
The problem: 
To assure that small electrodes mounted on elec-
trical discharge machines are aligned and true before 
starting the machining operation. Electrodes that are 
not exactly in alignment with the machine axis or 
that are slightly bent will generate cavities that are 
too large or incorrectly shaped. 
The solution: 
A shadowgraph system that projects a magnified 
image on a screen so that the alignment of the elec-
trode can be corrected and verified. 
How it's done: 
The system uses a conventional 500-watt slide 
projector as a light source. A Fresnel lens is posi-
tioned between the light source and the electrode to 
collect the light into an image-forming lens, or a 
projecting lens system, which forms an image of the 
electrode on a movable screen. The screen is placed 
at the position which provides the desired magnifi-
cation, but it is usually located fairly close to the 
machine where it can provide a magnification of 
about two. If a flat screen is placed at an oblique 
angle to the optical axis of the system, one dimension 
of the image can be effectively magnified more than 
the other, for example, the width of an electrode can 
be magnified by a factor of 6 to 8 while the mag-
nification of the length remains fixed. 
The path of motion of the center of the tool holder 
can be established on the screen as the tool holder 
is raised and lowered, and a fiducial line can be 
scribed on the screen to provide a reference for align-
ment of the electrode. Since the fiducial line and the 
electrode are constantly in view, the process of posi-
tioning and straightening the electrode can continue 
until the operator achieves the requisite accuracy of 
alignment. An electrode 12 to 15 cm in length and 
1 mm in diameter can be easily straightened to a 
runout well within 0.050 to 0.075 mm. 
The optical system makes it possible to machine in 
hard materials very small, straight holes to depths 
that are limited only by the length of the electrode. 
Moreover, adjustments and corrections of the elec-
trode can be made while work is in place, and the 
shape of the electrode can be readily monitored as 
machining progresses. 
This technique may be adapted to other machine 
tool equipment where physical contact with the tool 
(continued overleaf) 
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Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
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S
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cannot be made during inspection and where access 
to the tool is so limited that conventional runout 
checking procedures (such as dial indicators) cannot 
be used. 
Notes: 
1. An erecting lens can be placed between the pro-
jecting lens system and the screen to cast an 
upright image. Sharp images of the electrodes will 
be obtained only if the projecting lens system is 
properly constructed and corrected for aberrations. 
2. The screen can be curved to keep all portions of 
the image in focus; the curved screen compensates 
for optical aberrations due to finite depth of field 
of the imaging lens. 
3. Requests for further information may be di-
rected to:
Technology Utilization Officer 
Ames. Research Center 
Moffett Field, California 94035 
Reference: TSP72-10036 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035 
Source: A. G. Boissevain and

B. W. Nelson
Ames Research Center 
(XAC-09489) 
Category 07


Optical alignment of electrodes on electrical discharge machines

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