Drill bit eliminates delamination when drilling laminated material. It cuts or shaves the material as it progresses through it. The bit acts to hold down the material during drilling to prevent tearing or ripping and produces a clean, smooth and defect-free hole. It prevents chipping in stretched plastic windows for high-altitude, high-performance aircraft

Tillotson, R. N.

English

NASA Technical Reports Server

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December 1965
	 Brief 65-10386 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical information, Springfield, Virginia, 22151. 
Drill Bit Design Assures Clean Holes in Laminated Materials 
Narrowest 
Part 
The problem: In drilling laminated materials, drill bits 
have operated by a scraping action due to their zero-
to-negative radial rake angle. This has resulted in 
delamination due to tearing of the material at the ends 
of the holes and heat generated in bit and material. 
The solution: A drill bit of new design that cuts or 
shaves the material as it progresses through it. The 
bit acts to hold down the material during drilling to 
prevent tearing or ripping and produces a clean, 
smooth, and defect-free hole. 
How it's done:The body of the drill bit is formed by 
grinding hollows in each side of the body portion so 
that the narrowest part of the body is located at its 
exact center running from shank to tip. The widest 
points occur at the outer extremities of the body and 
the forward or tip portion of the drill has shoulders 
rounded to the diameter of the drilled hole to permit 
the drill to smoothly enter the material. 
As shown in the end portion view, a line drawn di-
agonally through a cross section of the bit passes 
through the exact center of the tip. This line repre-
sents 0° radial rake. The body is hollowed with a cir-
cular curve of a radius sufficiently short that angle A 
is formed by a tangent and the 0° line at the outer 
extremity of the bit. Such positive radial rake angles of 
from 1° to 15° have proven satisfactory. The curve 
of the hollow of the cutting edge decreases from a 
positive radial rake (angle A), to 0° radial rake (point 
B), then to a negative radial rake at angle C. This par-
ticular positive-to-negative radial rake is the feature 
that enables this drill bit to produce superior holes. 
Note: This invention was developed to prevent 
crazing or chipping in stretched plastic windows for 
high-altitude, high-performance aircraft where such 
defects cannot be tolerated. 
Patent status :Title to this invention has been waived 
under the provisions of the National Aeronautics and 
Space Act (42 U.S.C. 2457 (f)), to Douglas Aircraft 
Company, Inc.. 3000 Ocean Park Boulevard, Santa 
Monica, California. 
Source: Raymond N. Tillotson of Douglas Aircraft
Company, Inc. under contract to 
Western Operations Office 
(WOO-098)
Category 05 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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Drill bit design assures clean holes in laminated materials

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